Introduction to Histopathology MODULE

Histology and Cytology

1
Notes
INTRODUCTION TO
HISTOPATHOLOGY

1.1 INTRODUCTION
Surgical pathology includes gross and microscopic examination of resected
specimens and biopsies by histopathologists for tissue diagnosis. Several steps
are followed to get the tissue in a form, by which diagnosis can be made under
light microscope.

OBJECTIVES
After reading this lesson, you will be able to:
z list the steps involved in the processing of surgical specimens for
histopathologic examination
z explain the after care of the specimens
z explain grossing and gross room
z describe the laboratory hazards and safety measures.

Steps involved in the process are

1. Receipt of specimens from OT
2. Grossing
3. Tissue processing
4. Embedding
5. Section cutting
6. Staining and labelling
7. Dispatch of slides to pathologist for diagnosis

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 MODULE Introduction to Histopathology

Histology and Cytology Once the diagnosis is made, the slides come back to the laboratory. After the
reports are sent to the surgeons either as soft copy or hard copy, the laboratory
has to perform the following functions -
1. Slides are filed for future reference or teaching/research for at least 10 years.
2. Requisition forms are filed and/or stored in digital form for at least 10 years.
3. Specimens may be divided according to their use
Notes
(a) Well preserved specimens with representative lesion should be kept
for
z teaching
z research
z museum
(b) For future reference (6 months to 1 year)
(c) Discard – The specimens which are not required or not useful for any
of the above purpose should be discarded.
Apart from these essential functions, various other procedures are performed in
a surgical pathology laboratory depending upon the requirement, feasibility and
availability of instruments and qualified personnel.
z Cryosections
z Histochemical stains
z Immunohistochemistry
z Electron microscopy
z Advanced techniques like in-situ hybridization, immunoflourescence.

1.2 GROSSING
It is the process by which pathology specimens are inspected with bare eye to
obtain diagnostic information. Following points should be noted before the
tissue is processed for microscopic examination-
A. Identification of the specimen-confirmation of patient and anatomical site
from which the specimen has been obtained.
B. Clinical details
C. Gross description – written record of physical appearance of the specimen.
z Only a small portion from the large specimen can be subjected to
microscopic examination, hence gross examination should be done by a
skilled person.

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Introduction to Histopathology MODULE
z Only soft tissue can be cut into small blocks and processed directly. Histology and Cytology

z Bony specimens need to be decalcified before processing.

z Stones and teeth require special treatment.

Gross room
A. The size and features of surgical pathology gross room depend on the
number of specimens, number of staff pathologists and residents and type Notes
of institution.
B. The room should be large enough to permit the work to all the pathologists
simultaneously. The room should be well illuminated, ventilated and with
a exhaust fan to remove the formalin vapors.
Following items should be in a gross room.
(a) A cutting board. The fluid from the board must run directly into the sink.
(b) Shelves for specimen containers.
(c) Ready access to hot and cold water.
(d) Ready access to formalin.
(e) Box of instruments containing forceps of various size, scissors of various
types and size, probe, bone cutting saw or electric bone cutter, scalpel
handle, disposable blades, long knife and ruler to measure the size of lesion
and specimens.
(f) Box with cassettes and labels.
Apart from these items a good gross room should also have -
(a) Large formalin container
(b) Other fixatives
(c) Refrigerator
(d) Photographic facility
(e) Balance for gross specimens
(f) X-ray view box

1.3 LABORATORY HAZARDS AND SAFETY MEASURES

Gross room
1. Formalin vapors are irritant to eyes and throat. Exhaust may be used as
outlet for vapors.

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 MODULE Introduction to Histopathology

Histology and Cytology 2. One should always use mask, apron, eye glasses and gloves to protect
oneself from
z infected material

z formalin vapors

z spilt blood or any other fluid

3. Keep the grossing table clean with antiseptic solution.

Notes 4. All specimens should be in container with 10% formalin and covered with
lid.
5. After grossing specimen should be kept according to accession number.

1.4 HISTOPATHOLOGY LABORATORY

The laboratory should be large enough to accommodate various equipments and
personnel to work with ease. The equipments which are kept in this laboratory
are -
z Tissue processor

z Tissue embedding table

z Microtome

z Tissue warming plate

z Tissue flotation bath

z Slide stainer or glassware for manual staining

z Table to label and dispatch the slides.

The handling of the tissues and description and functioning of various

equipments is detailed in the respective lessons.

1.5 LABORATORY HAZARDS AND SAFETY MEASURES

Histopathology laboratory
1. Most of the equipments present in this laboratory are functioning 24x7 days.
Electrical connections should be checked before leaving the laboratory
every day.
2. Many chemicals are inflammable, hence care should be taken to avoid any
fire hazard.
3. Fire extinguisher should always be available.
4. Minimum inflammable substances should be kept in the laboratory.
Substances like wax, xylene alcohol, acetone should be stored at a separate
place.
5. Some chemicals are carcinogenic or harmful to the skin. Therefore staining
and other work should be performed with the gloves on.

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Introduction to Histopathology MODULE
Histology and Cytology

INTEXT QUESTIONS 1.1

1. Slides and requisition forms are preserved for future reference for atleast
................... years
2. Specimens may be divided according to their use as ..................., ...................
& ................... Notes
3. The process by which specimens are inspected with bare eyes to obtain
diagnostic information is ...................
4. Formalin vapors may be expelled from the gross room by the use of
...................
5. All specimens should be stored in ................... solution

WHAT HAVE YOU LEARNT

z Surgical pathology includes gross and microscopic examination of resected
specimens and biopsies for tissue diagnosis
z The steps of process of diagnosis are receipt of specimen, grossing, tissue
processing, embedding, section cutting, staining, labeling
z Slides and requisition forms are stored for atleast 10 years for future
references
z Specimens may be divided according to their use as well preserved
specimen for teaching, research and museum, for future reference from 6
months to 1 year or may be discarded
z Grossing is the process by which the specimens are inspected with bare eyes
to obtain diagnostic information
z Gross room should permit the smooth functioning of pathologists, should
also be well illuminated and ventilated with exhaust fan
z Gross room should also have cutting board, shelves, formalin, hot and cold
water, required instruments
z All the specimens should be stored in 10% formalin container
z Personal protective equipments like gloves, mask, apron, eye glasses should
be used for preventive occupational hazards
z Electric equipments should be cared for their functioning.

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Histology and Cytology

TERMINAL QUESTIONS
1. What is grossing
2. What are the precautions to be taken for maintaining the safety in the
laboratory

Notes 3. How should the gross room be built

ANSWERS TO INTEXT QUESTIONS

1.1
1. 10 years
2. For museum, future reference and teaching discard
3. Macroscopic examination
4. Exhaust fan
5. 10% Formalin

6 HISTOLOGY AND CYTOLOGY

 MODULE Special Light Microscopy

Histology and Cytology

3
Notes
SPECIAL LIGHT MICROSCOPY

3.1 INTRODUCTION
Microscopes are instruments designed to produce magnified visual or
photographic images of objects too small to be seen with the naked eye. The
microscope must accomplish three tasks: produce a magnified image of the
specimen, separate the details in the image, and render the details visible to the
human eye or camera. Compound microscopes are suitable for examination of
stained preparations. For some other special conditions we need special
microscopes like Dark-ground, phase contrast, polarizing and immuno-
fluorescence microscopes.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the principle of Dark-ground, phase contrast, polarizing and
immunofluorescence microscopy
z explain the uses of Dark-ground, phase contrast, polarizing and
immunofluorescence microscopy.

3.2 DARK GROUND ILLUMINATION

Conditions arise when specimen need to be visualized as unstained or living
cells. Since such specimens have refractive indices close to medium in which
they are suspended, bright field microscopy is difficult as there is not much
contrast.
Principle: Dark ground microscopy prevents direct light from entering the front
of the objective, only light which enters is which gets reflected or diffracted by
the specimen, thus making them appear bright in a dark background (Fig. 3.1).

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Histology and Cytology

objective lens

stage

condenser
lens Notes

Fig. 3.1: In dark ground illumination, no direct rays enter the objective. Only scattered
rays from the edged of structures in the specimen form the image.

Uses of Dark ground microscopy: Useful for spirochaetes, flagellates, cell

suspensions, flow cell techniques, parasites, autoradiography, and fluorescence
microscopy.
Disadvantage: Resolution is inferior to bright field microscopy. Does not reveal
internal details.

3.3 PHASE CONTRAST MICROSCOPY

Unstained and living biological material viewing by bright field and dark ground
illumination has problems of reduced illumination and resolution. To overcome
these problems, phase contrast microscopes are used.
Principle: It is an optical microscopy illumination technique that converts phase
shifts in light passing through a transparent specimen to brightness changes in
the image. The phase shifts themselves are invisible to the human eye, but
become visible when they are shown as brightness changes.
A practical implementation of phase-contrast illumination consists of a phase
ring (located in an aperture plane located somewhere behind the front lens
element of the objective) and a matching annular ring, which is located in the
conjugate primary aperture plane (location of the condenser’s aperture).
Two selected light rays, which are emitted from one point inside the lamp’s
filament, are focused by the field lens exactly inside the opening of the condenser
annular ring. Since this location is precisely in the front focal plane of the
condenser, the two light rays are then refracted in such way that they exit the
condenser as parallel rays. Assuming that the two rays in question are neither
refracted nor diffracted in the specimen plane (location of microscope slide),
they enter the objective as parallel rays. Since all parallel rays are focused in the

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Histology and Cytology back focal plane of the objective, the back focal plane is a conjugate aperture
plane to the condenser’s front focal plane (also location of the condenser
annulus). To complete the phase setup, a phase plate is positioned inside the back
focal plane in annulus.
Uses: It’s a quick and efficient way of examining unstained paraffin, resin and
frozen sections, studying living cells (cell cultures) and their behavior.
Notes

Phase-plate
Refracted or diffracted
light (phase altered
by specimen)

Specimen

Unobstructed light
(phase unaltered
by specimen)

Fig. 3.2: The microscope condenser carries series of annular rings to produce hollow
cones of light. Each objective requires a different size of ring, an image of
which is formed by the condenser in back focal plane of the objective
as a bright ring of light.

3.4 POLARIZED LIGHT MICROSCOPY

Light can be described as an electromagnetic vibration where there are many
planes of vibration. Natural light vibrates in many planes or directions, whereas
polarized light vibrates in only one plane. It can be produced by passing light
through a polarizer. Substances capable of producing polarized light are called
birefringent.
Principle: The dedicated polarizing microscope uses two polarizers. One,
always referred to as polarizer, is placed beneath the substage condenser. The
other is called analyzer and is placed between the objective and the eyepiece.
Looking through both polarizers, the light intensity is best when they are both
giving light vibrating parallel to each other. However, when the light vibration
is at right angles to each other, there is dark background. If a substance capable
of birefringence is placed between the two polarisers it gets visualized as
brightness against a black background.

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Uses: Medicine-Amyloid detection, collagen fibers, urates and other crystals. Histology and Cytology
Metallurgy, Ceramics.

3.5 FLUORESCENCE MICROSCOPY

Principle: Fluorescence is the property of some substances which, when
illuminated by light of a certain wavelength, will re-emit the light at a longer
wavelength. In fluorescence microscopy, the exciting radiation is usually ultra- Notes
violet wavelength or blue region.
A substance which possesses a fluorophore will fluoresce naturally (Primary or
autofluorescence) eg Vitamin A, chlorophyll.
Dyes, chemicals and antibodies added to tissues produce secondary fluorescence
of structures and are called fluorochromes. When antibodies labeled with
fluorochromes are used to detect particular antigens, the technique is called
Immunofluorescent technique and is widely used in medicine. Tissue antigens
most commonly demonstrable by Immunofluorescence are viruses, protozoa,
bacteria, enzymes, hormones, plasma proteins, cells and cell constituents.
Examples of fluorochromes: Fluorescein (apple green emission color), Rhodamine
(Orange-red color)

TERMINAL QUESTIONS
1. Define principle and uses of dark ground illumination
2. Define principle and uses of phase contrast microscope
3. Define principle and uses of polarizing light microscopy
4. Define principle and uses of fluorescence microscopy

HISTOLOGY AND CYTOLOGY 15

 MODULE Receiving of Surgical Specimens

Histology and Cytology

4
Notes
RECEIVING OF SURGICAL
SPECIMENS

4.1 INTRODUCTION
In the laboratory setting, numerous histological specimens are received throughout
the day for testing. It is important to maintain a systematic approach to ensure
that all samples are accounted for and are being received and tested appropriately.
Without it, there is a potential to misplace or lose samples.

OBJECTIVES
After reading this lesson, you will be able to
z explain the process of receiving surgical specimens

z describe preparation of gross room

z receive the samples, label the sample and store.

4.2 RECEIVING OF SURGICAL SPECIMENS

At the time of receiving the specimens, following points should be checked and
these points must match between requisition form and label on the sample
container
1. Name of the patient
2. Sex and age of patient
3. Registration no, OPD or indoor number
4. Type of sample like appendix or lymph node
After matching the above points carefully, accession number of the Histopathology
laboratory should be given on the requisition form and on the sample container
like it has been depicted in the form and sample bottle

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Receiving of Surgical Specimens MODULE
Histology and Cytology

Cover

Akash 25 yrs m
IP/OPD 200 34,
cervical lymph node
01/2012
Notes

10% formalin

Specimen container

Fig. 4.1: Specimen container

A register should be maintained for record and for future reference

Following points should be noted on the register (sample given)
1 Date
2 Accession number which was given by the pathology department
3 Patients name, age, sex
4 Patients registration number/ OPD/ indoor number
5 Type of sample
6 Number of samples received from one patient
7 Remarks / final diagnosis which may be entered later on
After receiving the samples the consultant should be informed for grossing. If
grossing to be done after some time, fixative should be put in all the samples
to prevent autolysis of the specimen.

4.3 PREPARATION OF GROSS ROOM

The routine work associated with a surgical pathology specimen includes gross
and microscopic examination. Proper preservation of tissues and processing of
the tissue are the most important aspects for correct diagnosis.

The size and features of the gross room depends on the number of specimens
and type of institution. Gross room should be well illuminated and ventilated.
It should have a gross station and racks to keep the specimen in order of
accession number.

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 MODULE Receiving of Surgical Specimens

Histology and Cytology Gross station – It should have ventilated hood.

1. Cutting board placed inside the metal box designed in such a fashion that
all the fluids should flow directly into the sink
2. Ready access to sink with hot & cold water
3. Formalin – stock and 10% buffered formalin
4. Box of instruments containing
Notes (a) Scissors
(b) Forceps
(c) Malleable probe
(d) Scalpel handle with disposable blades
(e) Long knife
(f) Scale
(g) Pins for attaching the specimens to corked surface if required
5. Containers with different fixatives
6. Bone cutter
7. Large disposal bin
8. Box with cassettes and labels
These are the essential items. Depending upon the pathology service being
rendered to the institution more sophisticated items may be added.
Apart from the above items following items may be of help in keeping the
records
1. Photographic facility
2. Refrigerator
3. Balance to weigh the gross specimen
4. X-ray view box
5. Other equipments for tissue bank facility
Sample Copy
Receiving Register
Date 01.08.2012
Acc. No. Name Age Sex Registration Type of Remarks /
No. specimen Diagnosis

01/2012 Akash 25 yrs M 20034 Cervical Lymph

Node

02/2013 Divya 30 Yrs F 20049 Fallopian tubes

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Receiving of Surgical Specimens MODULE
Histopathology Form (Sample Copy) Histology and Cytology

Acc. No – 01/2012

Akash 25 yrs M OPD Registraion

Indoor Registration 20034

Clinical Diagnosis – Tuberculosis – Tuberculosis lymphadenitis

Notes
Clinical Complaints

Radiological Findings

Name of Surgeon Signature Previous biopsy No.

Date of colletion: 1.8.2012

Type of specimen – Cervical lymph node

Any special request / remark

WHAT HAVE YOU LEARNT

z How to receive and hande the surgical specimens. It is paramount to the
success of the diagnosis of the specimen. High volumes, multiple steps and
multiple human interactions with specimens can create confusion. Therefore,
it is important to follow standard procedures which will help in smooth
function of the laboratory.

TERMINAL QUESTIONS
1. Write briefly about receiving and labelling of the specimen.
2. How do you prepare a gross room for examination of the specimen.

HISTOLOGY AND CYTOLOGY 19

Exfoliative Cytology MODULE
Histology and Cytology

21
Notes
EXFOLIATIVE CYTOLOGY

21.1 INTRODUCTION
Exfoliative cytology, which is a quick and simple procedure, is an important
alternative to biopsy in certain situations. In exfoliative cytology, cells shed from
body surfaces, such as the inside of the mouth, are collected and examined. This
technique is useful only for the examination of surface cells and often requires
additional cytological analysis to confirm the results.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the principle of exfoliative cytology
z explain the methods of sample collection for exfoliative cytology.

21.2 EXFOLIATIVE CYTOLOGY

Exfoliative cytology differs from the more precise sampling of known lesions,
like needle biopsy. It categorizes collected samples only by analyzing the
presence of abnormal or atypical cells, or by showing the presence of malignant
cells.
When a woman has a pap smear, she may have a result that show atypical cells.
If this is the first exfoliative cytology test that shows atypical cells, then usually,
the Pap smear is repeated in six to twelve months. If however, repeated showings
of atypical cells are present in exfoliative cytology results, further tests may be
undertaken to determine if cancerous cells are present.
Doctors or dentists may also use exfoliative cytology to check for the presence
of cancer in the mouth or throat. The test takes a few skin scrapings and can show

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Histology and Cytology the presence of either malignant or atypical cells. Malignant and atypical cells
will probably require a person to undergo a biopsy or closer examination of the
area in question to rule out cancer.

Cytologic examination of a serous effusion is of paramount importance because

the finding of cancer cells in such a specimen denotes that the patient has cancer
that is not only advanced but also almost always incurable. Apart from the
Notes finding of cancer cells, cytologic examination of pleural, peritoneal, and
pericardial effusions may also reveal information about inflammatory conditions
of the serous membranes, parasitic infestations, and infection with bacteria,
fungi, or viruses.

21.3 COLLECTION METHOD

In this method, cells are collected after they have been either spontaneously shed
by the body (“spontaneous exfoliation”) or manually scraped/brushed off of a
surface in the body (“mechanical exfoliation”). An example of spontaneous
exfoliation is when cells of the pleural cavity or peritoneal cavity are shed into
the pleural or peritoneal fluid. This fluid can be collected via various methods
for examination. Examples of mechanical exfoliation include Pap smears, where
cells are scraped from the cervix with a cervical spatula, or bronchial brushings,
where a bronchoscope is inserted into the trachea and used to evaluate a visible
lesion by brushing cells from its surface and subjecting them to cytopathologic
analysis.

Spontaneous exfoliation: Peritoneal fluid, pleural fluid, pericardial fluid, urine,

cysts, washings (peritoneal, bladder)

The fluid is collected into a clean, dry container, which need not be sterile, and
sent to the laboratory as soon as possible. If the fluid cannot be sent immediately,
it should be stored in a refrigerator at 40C and not allowed to freeze. We do not
require anticoagulant or fixative to be added to the fluid. The appearance to the
naked eye of a serous effusion sometimes reveals clues about the cause of the
effusion and the nature of its cellular contents. Therefore, for every serous
effusion received by the laboratory, note should be made of its volume, color,
clarity, and any unusual physical features, such as malodor, opalescence, or high
viscosity.

Mechanical exfoliation: Cervical pap smear, brushings (Bronchial, gastric,

biliary, oral, etc).

Cervical smear is a reliable method for diagnosis of cervical cancer. The smears
are usually taken in Gynecology ward or OPD, but sometimes patients are sent

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Exfoliative Cytology MODULE
to laboratory for smear purposes. Patients should be advised NOT to douche, Histology and Cytology
use vaginal medications, or have intercourse 24 hours prior to the pap smear
preparation. Patients should NOT schedule pap smear exams during menses.
These situations may obscure cellular details or remove diagnostic material from
the cervix or vagina. The smear is obtained under direct vision after introduction
of speculum. A wooden tongue depressor cut with scissors to fit the contour of
cervix may be used. Commercially prepared plastic or wooden scrapers are
Notes
widely available for this purpose. The scraper is rotated under pressure to 360°
for 4-5 full rotations. The material is spread on a pre-labelled slide and fixed
immediately.

Several types of brushes have also been introduced to overcome the disadvantages
of scrapers alone (not being able to reach endocervical canal and transformation
zone where the carcinomas originate).

Brushes are also used to scrape cells in respiratory tract, oral mucosa, esophagus,
stomach, duodenum, colon and biliary tract. It is preferable to obtain the brush
sample before the biopsy because the latter results in bleeding, which both
obscures the lesion, and detracts from the quality of a subsequently collected
cytologic sample, whereas interpretation of the biopsy is not affected by the
reverse order of collection. Collection of a good brush sample usually requires
an experienced assistant, because the operator may well be engaged in
maneuvering the end of the scope and holding the lesion in focus while the
assistant manipulates the brush. Therefore, it is ideal that a Cytology staff
member be present for immediate slide preparation of the specimen. They are
all taken under vision- direct or through fibreoptic endoscopy. In all these cases
a lot of care needs to be taken to make smear immediately from the brush by
gently rotating the brush on slides and fixing them immediately. The material
should not be crushed. If liquid-based cytology is used, the head of the broom
is detached and dropped into the preservative vial.

Once received in laboratory, the usual precautions need to be taken as discussed

in specimen receiving, handling and storage.

When only one slide is received, it should be preferable to stain it with

Papanicolaou stain. When multiple slides are received- some are air dried (stain
with MGG, special stains, etc) and some are wet fixed (stain with Papanicolaou).

The liquid specimens need to be commented upon the volume, color and
turbidity. Specimens need to be centrifuged and cytocentrifuged depending on
cellularity. After concentrating they can be used for both air dried smears and
wet fixation.

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 MODULE Exfoliative Cytology

Histology and Cytology

WHAT HAVE YOU LEARNT

z Exfoliative cytology is useful for the examination of surface cells
z Cells are collected either spontaneously shed by body or manually scraped
off of a surface in the body
Notes z Brushes have been introduced to overcome the disadvantages of scrapes
z Brushes are used to scrapes cells in respiratory tract, oral mucosa,
esophagus, stomach, duodenum, colon and biliary tract
z Care needs to be taken to make smear immediately from the brush by gently
rotating the brush on slides and fixing them immediately. The material
should not be crushed.
z If liquid-based cytology is used, the head of the broom is detached and
dropped into the preservative vial.
z When only one slide is received, it should be preferable to stain it with
Papanicolaou stain. When multiple slides are received- some are air dried
(stain with MGG, special stains, etc) and some are wet fixed (stain with
Papanicolaou).

TERMINAL QUESTIONS
1. Define exfoliative cytology.
2. Give examples of samples on which exfoliative cytology can be performed.
3. Enumerate few precautions to be taken while handling brush specimens.

134 HISTOLOGY AND CYTOLOGY

 MODULE Cryostat and Frozen Section

Histology and Cytology

15
Notes
CRYOSTAT AND FROZEN
SECTION

15.1 INTRODUCTION
Sections are prepared quickly for histological examination by freezing the tissue.
The section should be thin, and without water crystals. It is an important
procedure for quick diagnosis.

OBJECTIVES
After reading this lesson, you will be able to:
z enlist the indications of frozen section
z explain the disadvantages of frozen section
z describe cryostat.

15.2 PURPOSES OF FROZEN SECTION

Frozen sections are used for following purpose
z Quick diagnosis
z Study the margins of cancer
z Enzyme histochemistry
z Immunohistochemistry
z Detection of lipid
z Some molecular procedures

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Histology and Cytology
Disadvantages
z Morphology is distorted
z Cellular details are not well seen,
z Staining is not very good
z Some specials stains cannot be performed.

Handling of specimen Notes

Tissue must reach histopathology laboratory immediately. To avoid tissue being
dried it should be kept in saline. The size of the tissue should be small thin, so
that good smooth sections can be obtained and freezing is quick. Thickness of
the tissue should be about 3mm to 4mm.The tissue can directly be taken to
cryostat or can be fixed with 10% formalin or formol –alcohol

Embedding media
Sucrose (20%) or a drop of water may be applied on the chuck. Optimum
Cooling temperature (OCT) compounds or 20% sucrose gives good result. Other
embedding media are available with cryostat. Completion of freezing is
observed by the change of color of tissue which turns glossy white. Freezing
should be done fast. This will prevent ice crystal formation. The morphology
is better preserved and artifacts are less.

Different freezing substances are used depending upon the availability and
feasibility.

Carbon Dioxide gas is most commonly used with freezing microtome. This gives
good results. Liquid Nitrogen is another substance used for freezing the tissue.
An expertise is required while using liquid nitrogen to get uniform freezing.
Aerosol sprays are also used for this purpose.

Cryostat: Cryostat is used in medicine to cut histological sections. They are

usually used in a process called frozen section histology. The cryostat is
essentially an ultrafine “deli-slicer”, called a microtome, placed in a freezer. The
cryostat is usually a stationary upright freezer, with an external wheel for rotating
the microtome. The temperature can be varied, depending on the tissue being
cut - usually from minus 20 to minus 30 degree Celsius. The freezer is either
powered by electricity, or by a refrigerant like liquid nitrogen. Small portable
cryostats are available and can run off generators or vehicle inverters. To
minimize unnecessary warming all necessary mechanical movements of the
microtome can be achieved by hand via a wheel mounted outside the chamber.
Newer microtomes have electric push button advancement of the tissue. The

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 MODULE Cryostat and Frozen Section

Histology and Cytology precision of the cutting is in micrometres. Tissue are sectioned as thin as 1
micrometre. Usual histology slides are mounted with a thickness of about 7
micrometres.
Specimens that are soft at room temperature are mounted on a cutting medium
(often made of egg white) on a metal “chuck”, and frozen to cutting temperature
(for example at -20 degrees C). Once frozen, the specimen on the chuck is
Notes mounted on the microtome. The crank is rotated and the specimen advances
toward the cutting blade. Once the specimen is cut to a satisfactory quality, it
is mounted on a warm (room temperature) clear glass slide, where it will
instantaneously melt and adhere. The glass slide and specimen are air dried, and
stained. The entire process from mounting to reading the slide takes from 10 to
20 minutes, allowing rapid diagnosis in the operating room, for the surgical
excision of cancer. The cryostat section quality is poorer as compared to fixed
tissue sections.

INTEXT QUESTIONS 15.1

1. To avoid drying, the tissue should be kept in ......................
2. Tissues can be fixed with ......................
3. ...................... or ...................... is used as embedding media
4. ...................... gas is most commonly used with freezing microtome

WHAT HAVE YOU LEARNT

z Sections are prepared quickly for histological examination by freezing the
tissue
z Frozen section is used for quick diagnosis, studying margins of cancer,
enzyme histochemistry, Immunohistochemistry
z Tissues must reach the laboratory immediately and to prevent drying of
tissue it should be kept in saline
z The tissue can be fixed with 10% formalin or formal alcohol
z Optimum cooling temperature or 20% sucrose is used as embedding
medium
z Ice crystal formation may be prevented by freezing the specimen fast
z Carbon dioxide gas is most commonly used with freezing microtome
z Cryostat is used for cutting histological frozen sections

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Histology and Cytology

TERMINAL QUESTIONS
1. What is a cryosection?
2. Write two indications of cryosections.
3. What is a cryostat?
Notes
4. What are the substances used in cryostat to cool the device?
5. Write three embedding media used for cryosections.

ANSWERS TO INTEXT QUESTIONS

15.1
1. Saline
2. 10% formalin
3. Optimum cooling temperature or 20% sucrose
4. Carbon dioxide

HISTOLOGY AND CYTOLOGY 101

Lipid Stain MODULE
Histology and Cytology

13
Notes
LIPID STAIN

13.1 INTRODUCTION
The Oil Red O (ORO) stain can identify neutral lipids and fatty acids in smears
and tissues. Fresh smears or cryostat sections of tissue are necessary because
fixatives containing alcohols, or routine tissue processing with clearing, will
remove lipids. The ORO is a rapid and simple stain.

OBJECTIVES
After reading this lesson, you will be able to:
z explain the principle of lipid stain
z describe various reagents used for lipid stains
z describe the procedure of lipid staining.

13.2 LIPID STAIN

Aim: To demonstrate intracellular lipid in tissue sections.
Principle: The dye being more soluble in the lipid to be demonstrated than in
the vehicular solvent. The polyazo group of dyes includes the oil red series, the
sudan red series and sudan blacks. All these dyes are interchangeable and may
be substituted.
Sudan series - Sudan III
- Sudan IV
- Sudan black
Control - Lipid positive section

HISTOLOGY AND CYTOLOGY 83

 MODULE Lipid Stain

Histology and Cytology

Reagents
1. Oil Red O stock solution -
Oil Red O 0.5gm
Isopropanol 100ml
Dissolve the dye in isopropanol using gentle heat in water bath.
Notes 2. Oil Red O working solution
Stock Oil Red O solution 30ml
Distilled water 20ml
Dilute the stock solution with distilled water and keep it for 10 minutes,
filter and cover it immediately.
3. Glycerine Jelly Mounting medium
Gelatin 10gm
Distilled water 60ml
Glycerol 70ml
Phenol 0.25gm
Dissolve the gelatin in distilled water using sufficient heat to melt the
gelatin, add glycerol and phenol. Mix well and transfer to a small capped
bottle and refrigerate.

Procedure
z Fix timer in formalin, wash with running tap water for 5 to 10 minutes.
z Cut frozen section of 8 to 10 micron thickness and air dry.
z Rinse with 60% isopropanol.
z Stain with freshly prepared Oil Red O working solution for 15 minutes.
z Rinse with 60% isopropanol.
z Few dips in Alum hematoxylin to stain nuclei.
z Rinse with distilled water.
z Mount in water or glycerine jelly.

Result
z Lipid red
z Nuclei blue

84 HISTOLOGY AND CYTOLOGY

Lipid Stain MODULE
Note Histology and Cytology

z Use cryostat sections of 8 to 10 micron thickness or formalin fixed smears.

z working Oil Red O solution should be freshly prepared from stock solution
and kept in close container.
z Never take the sections through clearing solvent prior to mounting as this
will remove the lipid to be demonstrated. Notes
z Frozen sections should be used to stain neutral triglycerides.
z Lipoproteins may be demonstrated on paraffin sections.
z Alcohol fixation removes most lipids.

INTEXT QUESTIONS 13.1

1. Dyes used in lipid stain is .....................
2. ..................... is used to stain nuclei
3. Lipid is demonstrated by ..................... colour
4. Nuclei is demonstrated by ..................... colour
5. Lipoproteins may be demonstrated on ..................... section
6. ..................... fixation removes lipids

WHAT HAVE YOU LEARNT

z Lipid stain is used to demonstrate intracellular lipid in tissue sections
z Polyazo group of dyes like oil red series, sudan red series and sudan blacks
are the dye used for demonstrating lipids in tissue section
z The frozen section should be cut 8 to 10 micron thickness
z Lipids appear as red and nuclei appear blue
z Lipoproteins may be demonstrated on paraffin sections
z Alcohol fixation removes most lipids

HISTOLOGY AND CYTOLOGY 85

 MODULE Lipid Stain

Histology and Cytology

TERMINAL QUESTIONS
1. What is principle of lipid stain?
2. Name three dyes used to demonstrate lipid in tissue sections.
3. What precautions should be observed during lipid staining on tissue
Notes sections?
4. What should be the thickness of sections for lipid staining?
5. What is the mounting media used in lipid staining?

ANSWERS TO INTEXT QUESTIONS

13.1
1. Sudan series
2. Alum hematoxylin
3. Red
4. Blue
5. Paraffin
6. Alcohol

86 HISTOLOGY AND CYTOLOGY

Fine Needle Aspiration Cytology MODULE
Histology and Cytology

30
Notes
FINE NEEDLE ASPIRATION
CYTOLOGY

30.1 INTRODUCTION
The use of fine-needle aspiration (FNA), a method of aspiration biopsy cytology,
continues to grow throughout the World. Improvements in imaging, computed
tomography scan (CT), and ultrasound (USG) have fueled the growth of FNA
among both radiologists and clinicians. The dominant clinical sites for FNA still
remain breast, thyroid, and lymph nodes among superficial tissues.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the techniques of fine needle aspiration cytology
z arrange the clinic for performing FNAC
z assist the pathologist in performing FNAC
z make smears and collect any fluids obtained from FNAC and process
appropriately.

30.2 CLINICAL SKILLS REQUIRED

Aspiration biopsy may be indicated whenever there is a palpable tumor mass or
a lesion visualized within any organ. For the physician or more specifically for
the pathologist performing FNA, some familiarity with general anatomy is
essential. For the physician or more specifically for the pathologist performing
FNA, some familiarity with general anatomy is essential. For the pathologist
performing this biopsy some sharpening of clinical skills, both obtaining a

HISTOLOGY AND CYTOLOGY 175

 MODULE Fine Needle Aspiration Cytology

Histology and Cytology focused clinical history and performing a physical examination are required.
Clinicians performing aspiration biopsy obviously lack this essential ingredient
of experience and knowledge of morphology. Despite the recognized participation
and value of cytotechnologists to an aspiration biopsy service, the pathologist
must be actively involved in the aspiration biopsy, making both the initial and
final evaluation of the smears.

Notes The Thin-needle Aspiration Method

Thin needle generally 22, 23, 25, and 27 gauge, are used for the performance
of aspiration biopsy, most often 1.5 in. in length. Special situations may dictate
shorter needles and even higher gauge. For example, the very small cutaneous
metastasis of breast carcinoma on the chest wall may be sampled more easily
with a 27-gauge, 1-in. or even ½-in. needle and with a small, 3.0- to 5.0-mL
syringe, approaching the nodule in a plane perpendicular to the skin surface, in
the manner of performing a tuberculin skin test. Radiologists most often use the
Chiba needle of 21 and 22 gauge for transthoracic and transabdominal
aspirations. If one employs only the thin-needle technique, there are virtually no
complications, the exceptions being FNA of the thorax (pneumothorax) or some
cases of excessive bleeding with transabdominal aspiration biopsy.

Basic Equipment
The basic equipment used for rapid and efficient performance of thin-needle
aspiration biopsy are as follows.
1. Cameco Syringe Pistol, Aspir-Gun, or other type aspiration handle;
2. 10 or 20-mL disposable plastic syringe with LuerLok or straight tip,
depending on aspiration gun handle size;
3. 22 to 27-gauge, 0.6- to 1.0-mm external diameter disposable needles, 3.8
and 8.8 cm, 15 and 20 cm long, with or without stylus; the needle hub should
be clear;
4. Alcohol skin preparation sponges; betadine skin sponges for deeper
aspirations, transabdominal, transthoracic, bone (where the cortex is not
intact or the periosteum is elevated), or deep soft tissue;
5. Sterile gauze pads;
6. Microscopic glass slides with frosted ends;
7. Small vial of balanced salt solution and/or RPMI tissue culture transport
media;
8. Suitable alcohol spray fixatives for immediate fixation of wet smears

176 HISTOLOGY AND CYTOLOGY

Fine Needle Aspiration Cytology MODULE
9. 10 or 20 mL capped tube with 10% neutral buffered formalin for cell-block Histology and Cytology

10. Optional vial of local anesthesia, 1-2% lidocaine; topical spray anesthesia
for aspirates in children or intraoral aspirates; vials of lidocaine that
dentists use for local anesthesia and the dispensing equipment may be
useful;
11. Small vial of buffered glutaraldehyde for fixing aspirate for electron
microscopy if required or anticipated. Notes
A small plastic tray easily holds all the equipment. Majority of the smears are
to be air-dried and later stained with a Romanowsky method, the Diff-Quik stain
being preferred. Some smears are usually wet-fixed in 95% ethyl alcohol.

Aspiration Technique
To be successful with an aspiration biopsy, it is important to follow the
preliminary steps listed here:
1. Review the history of the patient. Determine the clinical problem and its
relevance to the lesion to be biopsied.
2. Determine whether the biopsy is justified.
3. Palpate the mass, attempting to determine its location in relation to
surrounding structures. Estimate its depth. Decide on the optimal direction
of the needle to accomplish the aspiration biopsy. A mass located deeply
in tissue in usually best approached perpendicularly to the skin surface.
Small and superficially lying tumors are best approached by penetrating the
skin at or very close to a horizontal plane, then feeling for the mass with
the needle tip.
4. The patient should be placed in a comfortable position for the aspiration
biopsy, but the mass must be easily palpable and immobilized during the
biopsy.
Step 4 is very important for head and neck lesions. The prominence of an
enlarged lymph node, or lump, may sometimes depend on whether the
patient is supine or erect. The sternocleidomastoid muscle bulk and its close
proximity to the cervical lymph nodes require positioning the patient such
that the biopsy needle passes through only a minimum of soft tissue and
muscle before reaching the target. Avoid aspirating a mass by traversing the
sternocleidomastoid muscle. For the aspiration of thyroid lesions, it is
usually helpful to place a small pillow under the patient’s upper back,
extending the neck with the head tilted back.
5. Take time to examine the patient thoroughly. Discuss your preliminary
assessment of the patient’s lesion. This is an opportunity to describe what

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 MODULE Fine Needle Aspiration Cytology

Histology and Cytology will take place during the aspiration and what is to be accomplished with
it.
6. Obtain informed consent. This consent should indicate that name of the
patient who is having the aspiration, the name of the doctor performing the
aspiration and a listing of discussed complications.

Notes 30.3 PERFORMING THE FNAC

It is essential that the FNAC be performed by a doctor who has knowledge of
anatomical structures and pathological lesions expected in the particular region.

Smear Preparation
1. Immediately after completing the aspiration biopsy, the needle should be
quickly removed from the syringe; pulled back on the syringe pistol to fill
the syringe with air.
2. The needle should be reattached and placed near the center and touching
the surface of a plain glass slide.
3. Advancing the plunger of the syringe, will express a small drop of the
sample, approximately 2–3 mm in diameter, onto the slide.
4. This procedure should be quickly continued over a series of five to six
slides.
5. Invert another plain glass slide over the drop; as it spreads from just the
weight of the slide, pull the two slides apart horizontally in a single gentle
motion.
6. As an alternative, when the drop spreads in a circular fashion, again from
the weight of the slide, pull the two slides apart vertically (compression or
pop smears).
7. Repeat the above procedure for all slides; fix some of the slides immediately
in 95% ethyl alcohol, or other suitable fixatives, depending on stain
preferences, as you make each smear.
8. Allow unfixed smears to air-dry.
Smears are appropriately stained later in the cytology laboratory.

30.4 ORGANIZATION OF THE ASPIRATION BIOPSY

SERVICE
Sufficient space to examine patients is required. For the in-hospital clinic it
should be located close to the pathology department but should be a separate
designated area that is quiet and comfortable for patients and with sufficient
178 HISTOLOGY AND CYTOLOGY
Fine Needle Aspiration Cytology MODULE
support staff to register patients, provide assistance to the pathologist performing Histology and Cytology
the aspiration, and take care of all clerical matters.
There are a number of considerations in developing and planning a free-standing
clinic.
1. Location
a. Convenience Notes
b. Ground floor
c. Within an established medical facility
d. Near offices of physicians referring the majority of the patients
2. The facility
a. Two examining rooms, one somewhat larger than the other
b. Some counters at waist level for standing
c. Examining table pointed toward outside windows and away from
aspiration instruments and smear preparation area

TERMINAL QUESTIONS
1. What are the equipments required for FNAC?
2. Enumerate the various points to consider while planning an FNAC clinic.
3. Describe the method of smear making in FNA laboratory.
4. What are the usual stains used for staining FNA smears and their fixatives?

HISTOLOGY AND CYTOLOGY 179

Cytologic Screening MODULE
Histology and Cytology

26
Notes
CYTOLOGIC SCREENING

26.1 INTRODUCTION
Screening of diseases gained significance in medicine at the end of the
nineteenth century, when public health authorities emphasized the importance
of screening methods for certain diseases. In 1941, George Papanicolaou
demonstrated a test for the early detection of cervical cancer, contributing toward
the creation of screening programs. Prevention and early diagnosis are major
factors in reducing morbidity and mortality resulting from neoplasia. Screening
of diseases involves a test or examination that can detect the existence of a
particular disease in a high-risk population, asymptomatic or with minimum
symptoms of the disease.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the basics of cytologic screening
z explain the steps involved in cervical cancer screening.

26.2 CYTOLOGICAL SCREENING

Screening of a particular disease requires a precise test, easy to do, at a low cost,
and the capability of detecting the presence of a lesion. Cancer of the uterine
cervix is an important cause of morbidity and mortality among women
worldwide and a leading public health problem. It is the second most common
cancer in women, but the most common in developing countries. Because of the
phases that precede the lesion in the natural progress of invasive cervical cancer,
and because they can be easily discovered and treated, the disease is well suited

HISTOLOGY AND CYTOLOGY 155

 MODULE Cytologic Screening

Histology and Cytology to screening programs. The Papanicolaou test is an established method for
examining the cells collected from the cervix to determine whether they show
signs of pre-neoplastic differentiation. Cytologic screening programs have led
to a large decline in cervical cancer incidence and mortality in developed
countries. However, cervical cancer remains largely uncontrolled in high risk
developing countries because of ineffective or no screening.

Notes Cervical cancer can be avoided when there is an early diagnosis of the precursor
lesions, without local or systemic compromise. Among the methods available
for early detection of cervical cancer, exfoliative cytology, or the Pap test, is
recommended worldwide for mass screening, because the efficacy in the
detection of premalignant lesions, associated with the social role of the method,
permits minimization of costs with curative medicine.

The basic integrated actions include: (1) care with collection, (2) processing of
the smears, (3) screening and interpretation of the specimens, (4) follow-up of
the patients, and (5) quality control.

1. Care with collection: The majority of false-negatives arise from problems

with collection of specimens, and for this reason this stage should be
systemized and there should be training and recycling of the personnel
responsible for taking the samples. The smears must be well identified, slim,
uniform, and without contaminants, and contain samples from the
transformation zone, where in the majority of cases the cervical cancer
develops. There should be a minimum of blood, mucus, or other obscuring
material such as lubricating gel. It is also important at this moment to
adequately fix the material so as not to compromise subsequent stages.
2. Processing the specimens: One of the characteristics of the Pap test is that
it consists of various stages. Each stage should be monitored so as to
minimize the possibility of error. The condition on arrival of the slides, and
the number of slides per case, must be verified. Special care should be taken
with the flow of the tests, with adequate numbering and balanced coloration
with control of the number of cases colored in each set. The end product
of this stage will be fundamental to a good result with the rest.
3. Screening and interpretation of the specimens: The screening should be
done in as little time as possible, depending on the basic requirements of
each program, by trained and qualified personnel. Care should also be taken
with excess workloads for cytopathologists and cytotechnicians, and also
with refresher courses and recycling. The report on the tests should be
systemized and use a unique nomenclature, of which all involved in the
preparation and interpretation of the results should be fully aware.

156 HISTOLOGY AND CYTOLOGY

Cytologic Screening MODULE
4. Follow-up of patients: Mere detection of the lesions will not determine Histology and Cytology
the impact on the natural history of the disease. For this reason the treatment
of lesions in a pre-invasive stage is fundamental.
5. Quality control: Quality is fundamental in gynecological cytopathology.
One of the greatest problems in mass cytology is the false-negative cases.
Cytopathology labs must have mechanisms for internal quality control with
the objective of avoiding false-negative and false-positive tests. External Notes
quality control must be included in the design of the prevention program.

26.3 THE ROLE OF LABORATORY IN SCREENING

PROGRAMS
The laboratory can make an important contribution to the structuring and
organization of cervical screening programs based on the Papanicolaou test. The
lab, when integrated into a screening program, should have among its objectives
top quality production, training, and updating of personnel and the guarantee of
a secure place of work, where risk factors are under control and the environment
is protected.

The system of internal monitoring of laboratory quality includes a set of actions,

which should be developed and disseminated in a coordinated way, involving
the various stages in the work process, from collecting a sample to issuing the
report. The system aims to accompany and evaluate the cyto- and histopathologic
diagnostic procedures in the laboratories, thus helping to determine areas where
improvements can be planned and implemented, and also evaluate the impact
of these actions and the incorporation of new practices.

The majority of cervical cancer occurs in developing countries. The success of

cervical cancer screening is shown by its ability to reduce the incidence of
cervical cancer and the resulting mortality. The integration of procedures is
essential for a successful screening program. Recently new technologies for
alternative and complementary forms of screening such as liquid-based cytology
and automated cytology have been proposed. A combination of methods has
been proposed in an attempt to improve the sensibility of the Pap test. Among
these, the association of cytology with the molecular test for HPV using hybrid
capture has been highlighted. Automated cytology may be used for the purpose
of reducing human errors caused by human fatigue, and to detect lesions with
a lesser number of abnormal cells in the sample. HPV vaccine will be an
additional tool in the strategies to reduce morbidity and mortality from cervical
cancer and will be a component of a comprehensive strategy with the long-term
goal of eliminating the disease. Cytologic screening can also be performed in
selected high-risk populations for lung, esophageal, and bladder cancer.

HISTOLOGY AND CYTOLOGY 157

 MODULE Cytologic Screening

Histology and Cytology

WHAT HAVE YOU LEARNT

z Screening of diseases gained significance in medicine at the end of the
nineteenth century
z George Papanicolaou demonstrated a test for the early detection of cervical
Notes cancer, contributing toward the creation of screening programs
z Prevention and early diagnosis are major factors in reducing morbidity and
mortality resulting from neoplasia
z Screening of diseases involves a test or examination that can detect the
existence of a particular disease in a high-risk population, asymptomatic
or with minimum symptoms of the disease
z The Papanicolaou test is an established method for examining the cells
collected from the cervix to determine whether they show signs of pre-
neoplastic differentiation
z The smears must be well identified, slim, uniform, and without contaminants,
and contain samples from the transformation zone, where in the majority
of cases the cervical cancer develops
z The screening should be done in as little time as possible
z A combination of methods has been proposed in an attempt to improve the
sensibility of the Pap test

TERMINAL QUESTIONS
1. What is meant by screening for a disease?
2. Name few common diseases for which cytology can be used as a tool.
3. What are the actions involved in pap smear screening program?

158 HISTOLOGY AND CYTOLOGY

 MODULE Cytology : Specimen Processing & Staining

Histology and Cytology

23
Notes
CYTOLOGY : SPECIMEN
PROCESSING & STAINING

23.1 INTRODUCTION
Laboratory sample processing includes steps from the receipt of the specimen
in the laboratory to the delivery of a stained slide rea140dy for microscopic
examination.
Throughout processing, the identity and integrity of the specimen must be
maintained, and the principles of universal precautions followed.

OBJECTIVES
After reading this lesson, you will be able to:
z describe various methods of cytology sample processing
z explain the methods of slide staining
z dispatch labeled slides and forms for cytoscreening.

23.2 SPECIMEN PROCESSING

The laboratory should confirm the identity and integrity of the specimen
received. Specimens are accepted only when ordered by physicians or other
persons authorized by law. Each sample must have a request completed by the
authorized provider prior to processing.
1. Specimen Preparation
(a) Smears
The preparation objective of direct smears is a slide with an evenly and
thinly applied cellular specimen that is free of mechanical distortion and
140 HISTOLOGY AND CYTOLOGY
Cytology : Specimen Processing & Staining MODULE
free of drying artifact when the slide is fixed in alcohol. Smears fixed in Histology and Cytology
alcohol (wet fixation) are usually stained by the Papanicolaou method; air-
dried smears are usually stained with a Romanowsky stain. Smears
preserved with spray fixatives should be soaked in 95% alcohol.
(b) Liquid Specimens
Liquid specimens should be processed according to the manner in which
they are submitted. Liquid specimens may be received fresh, with heparin, Notes
with preservative (alcohol or other fixative), or with physiologic solution
or tissue culture medium. Additional processing should be considered for
grossly bloody specimens prior to slide preparation. Blood clots should be
removed and processed as a cell block.
Specimens of low cellularity and low volume may be cytocentrifuged
directly. High volume specimens are usually concentrated prior to preparation.
Centrifugation is frequently used with the re-suspended pellet used for
direct smears.
2. Specimen staining
The Papanicolaou stain is recommended for the staining of alcohol fixed
cytology slides. Romanowsky stains may also be used for wet fixed slides,
but are primarily applied to air-dried smears.
(a) Papanicolaou Stain
The Papanicolaou stain uses a standard nuclear stain, hematoxylin, and two
cytoplasmic counterstains, OG-6 and EA. The outcome of this method is
crisp nuclear detail and transparency of the cytoplasm, which allows the
examiner to clearly visualize cellular morphology. Either a progressive or
regressive technique may be used for nuclear staining. Several automatic
programmable stainers are available.
(b) Romanowsky Stain
A Romanowsky stain is recommended for air-dried smears. Romanowsky
stains, mixtures of eosin and methylene blue, are a family of polychrome
stains that produce their effect by the production of azure dyes as a result
of demethylation of thiazines and the acidic component eosin. Unlike the
Papanicolaou stain they are metachromatic. Most Romanowsky stains used
in cytology are aqueous stains as opposed to the methyl alcohol based stains
of hematology. Many commercial stains are available, and most consist of
a methanol-based fixative, and two dyes which result in differentiation of
cytoplasmic and nuclear components. Most Romanowsky stains are rapid
and are useful in enhancing pleomorphism, and distinguishing extracellular
from intracytoplasmic material.

HISTOLOGY AND CYTOLOGY 141

 MODULE Cytology : Specimen Processing & Staining

Histology and Cytology 3. Dehydration, Clearing and Coverslipping

(a) Dehydration and Clearing
After staining, the sample is dehydrated by a series of increasing
concentrations of alcohol followed by rinsing in clearing solutions. The last
clearing solution should be colorless and its refractive index should be close
to that of the coverslip, slides and mounting medium. Xylene is the most
Notes commonly used clearing agent. Xylene clearing must be performed in a well
ventilated area or fume hood to limit exposure to xylene fumes. Slides
should remain in the clearing agent until coverslipping is performed.
(b) Coverslipping
Mounting medium used to bond the slide and the coverslip should be
compatible with the clearing agent, transparent, and have a refractive index
similar to the glass slide and the stained specimen. Adequate mounting
medium should be applied to protect the cellular material from air-drying
and shrinkage, and to prevent fading of the cell sample. The cellular material
should be covered by a suitably sized coverslip or covering material of
appropriate quality.
Different methods used to coverslip include placing the mounting medium
on the coverslip, then inverting the coverslip onto the slide surface, or
lowering the slide onto a coverslip containing adequate mounting medium.
Glass coverslips, coverfilm and automated coverslippers are available.
Ideally, the mounting medium should be allowed to dry before the slides
are reviewed to reduce movement of cellular material during the slide
examination. Chemical waste collected throughout the staining, dehydration,
clearing and coverslipping processes must be disposed of or recycled.
The stained and labeled slide(s) should be matched with its requisition or
other laboratory document that displays the same information. The
information on the slide must correspond to the information on the
requisition or laboratory document.

INTEXT QUESTIONS 23.1

1. Smears fixed in alcohol are stained by ................... method
2. Air dried smears are stained with ................... stain
3. Specimens of low cellularity and low volume may be ................... directly
4. ................... is the most commonly used clearing agent

142 HISTOLOGY AND CYTOLOGY

Cytology : Specimen Processing & Staining MODULE
Histology and Cytology

WHAT HAVE YOU LEARNT

z Laboratory sample processing includes steps from the receipt of the
specimen in the laboratory to the delivery of a stained slide ready for
microscopic examination.
z Throughout processing, the identity and integrity of the specimen must be
maintained, and the principles of universal precautions followed. Notes
z The preparation objective of direct smears is a slide with an evenly and
thinly applied cellular specimen that is free of mechanical distortion and
free of drying artifact when the slide is fixed in alcohol
z Smears fixed in alcohol (wet fixation) are usually stained by the Papanicolaou
method
z Air-dried smears are usually stained with a Romanowsky stain. Smears
preserved with spray fixatives should be soaked in 95% alcohol.
z Specimens of low cellularity and low volume may be cytocentrifuged
directly. High volume specimens are usually concentrated prior to preparation
z The Papanicolaou stain is recommended for the staining of alcohol fixed
cytology slides
z After staining, the sample is dehydrated by a series of increasing
concentrations of alcohol followed by rinsing in clearing solutions
z Xylene is the most commonly used clearing agent
z Mounting medium used to bond the slide and the coverslip should be
compatible with the clearing agent, transparent, and have a refractive index
similar to the glass slide and the stained specimen.

TERMINAL QUESTIONS
1. Write briefly about objective of smear making.
2. Write about manners of liquid specimen preparation.
3. What are the main staining methods used in cytology
4. Briefly write about the methods of coverslipping.

ANSWERS TO INTEXT QUESTIONS

23.1
1. Papanicolaou
2. Romanowsky
3. Cytocentrifuged
4. Xylene

HISTOLOGY AND CYTOLOGY 143

 MODULE Cytology : Disposal of Human Waste

Histology and Cytology

24
Notes
CYTOLOGY : DISPOSAL OF
HUMAN WASTE

24.1 INTRODUCTION
Hospital waste is “Any waste which is generated in the diagnosis, treatment or
immunization of human beings or animals or in research” in a hospital. Hospital
Waste Management means the management of waste produced by hospitals
using such techniques that will help to check the spread of diseases through

OBJECTIVES
After reading this lesson, you will be able to:
z describe various methods of cytology waste disposal
z practice safe disposal of human and chemical waste.

24.2 DISPOSAL OF HUMAN WASTE

The laboratory should conform to the local practices and guidelines for safe
disposal of human and chemical waste generated in the laboratory.
Hospital Waste categories and Disposal
Option Waste Category Treatment & Disposal
Category 1 Human anatomical waste Incineration /deep burial
Category 2 Animal waste Incineration /deep burial
Category 3 Microbiology & Incineration /deep burial
biotechnology waste

144 HISTOLOGY AND CYTOLOGY

Cytology : Disposal of Human Waste MODULE
Histology and Cytology
Category 4 Sharps Incineration / disinfection /
chemical treatment /mutilation
Category 5 Medicines and cytotoxic Incineration / destruction and
drugs disposal in secured landfill
Category 6 Solid waste (Blood Autoclave/chemical treatment/
and Body fluids) burial
Notes
Category 7 Solid waste (disposable Autoclave/chemical treatment/
items) burial
Category 8 Liquid waste ( blood Disinfection by chemicals/
& body fluids) discharge into drains
Category 9 Incineration Ash Disposal in municipal landfill
Category 10 Chemical waste Chemical treatment/ secure
landfill

24.3 WHO MEDICAL WASTE CATEGORIES

Infectious
Materials containing pathogens if exposed can cause disease.
z Human anatomical waste: waste from surgery and autopsies on patients with
infectious diseases;
z Sharps: disposable needles, syringes, saws, blades, broken glasses, nails or
any other item that could cause a cut;
z Pathological: tissues, organs, body parts, human flesh, fetuses, blood and
body fluids;

Non Infectious (Hazardous)

z Pharmaceuticals: drugs and chemicals that are returned from wards, spilled,
outdated, contaminated, or are no longer required;
z Radioactive: solids, liquids and gaseous waste contaminated with radioactive
substances used in diagnosis and treatment of diseases like toxic goiter.

Non Infectious (Non Hazardous)

z Domestic waste: from the offices, kitchens, rooms, including bed linen,
utensils, paper, etc.

HISTOLOGY AND CYTOLOGY 145

 MODULE Cytology : Disposal of Human Waste

Histology and Cytology Care needs to be taken to dispose off the Infectious and non-infectious hazardous
waste. The non Infectious (Non Hazardous) waste can be disposed off with
regular garbage disposal.
Cytology laboratory generates waste in the form of remnants of fluids
(peritoneal, pleural, cysts, etc), sputum, and left over specimen of liquid
cytology. The specimens need to be discarded only after chemical decontamination
using at least 1% sodium hypochlorite solution; and then discharged into drains/
Notes sewers where it is taken care of by the principle of dilution and dispersal.
Any solid waste needs to be disposed off according to hospital waste
management. Before disposal the specimen need to be segregated after proper
identification.

Segregation by color coding system

Three categories
z Infectious waste - Red bags
z Domestic waste - Green Bags
z Sharps - Needle cutters / Puncture proof containers

Transportation
z Containers: puncture proof, leak proof,
z Bags: sturdy, properly tied
z Transport trolleys: designated & timely
z Staff protection: provided with protective clothing and other items
z Never put hands in a bag
The infectious material in red bags will go for incineration.
The sharps can either go to incinerator or following autoclaving/chemical
disinfection can be mutilated. They should never be thrown in regular garbage.
Chemical waste collected throughout the staining, dehydration, clearing and
coverslipping processes must be disposed of or recycled according to state and
local regulations.

INTEXT QUESTIONS 24.1

1. Specimens before discarding need to be decontaminated with ................
2. Infectious waste is discarded in ................ colour bag
3. Domestic waste is discarded in ................ colour bag
4. Sharps are discarded in ................ container

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Histology and Cytology

WHAT HAVE YOU LEARNT

z Hospital waste is “Any waste which is generated in the diagnosis, treatment
or immunization of human beings or animals or in research” in a hospital
z Hospital Waste Management means the management of waste produced by
hospitals using such techniques that will help to check the spread of diseases Notes
through
z WHO categories waste as Infectious, Hazardous Non-infectious and Non-
hazardous non-infectious
z The specimens need to be discarded only after chemical decontamination
using at least 1% sodium hypochlorite solution; and then discharged into
drains/sewers where it is taken care of by the principle of dilution and
dispersal
z Any solid waste needs to be disposed off according to hospital waste
management. Before disposal the specimen need to be segregated after
proper identification.
z Segregation is by color coding system as Infectious waste - Red bags,
Domestic waste - Green Bags, Sharps - Needle cutters / Puncture proof
containers

TERMINAL QUESTIONS
1. What are the categories of hospital waste?
2. What are the WHO categories of medical waste?
3. What are the main methods of medical waste disposal?
4. What is the color coding for waste disposal?

ANSWERS TO INTEXT QUESTIONS

24.1
1. 1% sodium Hypochlorite
2. Red
3. Green
4. Blue / Puncture resistant

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Cytology : Specimen Collection & Storage MODULE
Histology and Cytology

22
Notes
CYTOLOGY : SPECIMEN
COLLECTION & STORAGE

22.1 INTRODUCTION
Cytology is the field of diagnostic medicine which deals with study of individual
cells and/or tissue fragments spread on glass slides and stained. The final quality
of cytodiagnosis depends to a large extent on quality of preparation of the
material. It has an advantage of providing a rapid diagnosis. Cytological study
can be done on various discharges from body (urine, nipple, sputum, vaginal,
sinus, etc), scrapings obtained (buccal mucosa, gastric, respiratory), tap done
from fluid collected in body (pleural, peritoneal, pericardial) or aspiration from
palpable lumps.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the principle of cytology
z explain the methods of sample collection & receiving
z learn how to store the specimen for examination.

22.2 HEALTH AND SAFETY

There are potential hazards in handling fluid specimens like unfixed sputum,
urine and other body fluids. All employees should be aware of all health and
safety aspects of laboratory, including fire drills, storage and disposal of
chemicals, use of electrical equipment, storage and disposal of biological
infectious material.

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 MODULE Cytology : Specimen Collection & Storage

Histology and Cytology Modern approach is to use ‘Universal Precautions’ to treat all unfixed specimens
with care and to handle them in biological safety cabinets. Centrifuges should
use sealed buckets.

Main aspects of safety in cytology laboratory

1. Specimen reception- suitable container (disinfectant, autoclave proof);

availability of suitable disinfectant (hypochlorite); protocol for leakage/
Notes
spillage

2. Specimen preparation- Protective clothes, coats, gloves, eye protection etc;

Safety cabinet, Disposal pots with disinfectant, Refrigerator for specimen
storage

3. Specimen disposal- Disposal protocol, Autoclave, clinical waste collection

4. Fire hazards and evacuation procedure

5. Storage of chemicals- Inflammables, Poisons, Toxic substances

6. First aid

22.3 SPECIMEN COLLECTION

Most specimens are received in the laboratory either as direct cell spreads (on
slides) or as cell suspensions (fluids). Most of Hospitals have FNA (fine needle
aspiration) clinic where FNA is done by cytopathologist. Medical technologist
is required in the clinic to spread the sample on glass slides and fix the slides
appropriately. Some clinics also perform rapid staining to check adequacy of
material.

22.4 TRANSPORT AND INFORMATION

Specimens should be sent to the laboratory as early as possible in suitable
containers. Lids should be properly secured to prevent any leakage and
specimens should be sealed in plastic bags. Glass slides should be kept in
suitable slide boxes. All specimens and slides should be properly labeled with
patient’s name and number. Fixed smears should be submitted in containers that
protect against breakage. Slide containers are available in a variety of shapes,
volumes and material. Optimal design features include easily opened containers
which stay closed during transport, shock resistant material, and enough room
to prevent slides from adhering to one another or the container. The slides should
be marked clearly with the patient’s name, as well as other identifiers if possible.
If more than one site is sampled, the slides must be clearly marked as to their

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site. Slides in fixative should be submitted in leak proof containers that protect Histology and Cytology
against breakage and are clearly labeled with the patient’s name and specimen
site(s).

Each fluid specimen should be placed in a clearly labeled container that is leak
proof. Enclosure in a transport bag indicating biohazardous contents is careful
if a courier system or manual delivery is planned. Paper requisitions that
accompany slides in fixative should be placed in an outside pocket to avoid Notes
exposure to any leakage of fixative. Needles should never be transported with
fluid specimens. Large glass collection containers should be avoided.

Specimen should be accompanied by properly filled requisition form. The

requisition must also provide space for the date the sample was collected, the
test to be performed, the source of the material, and the name and address or
other suitable identifiers of the authorized person requesting the test. The
request form should contain essential patient identification data- name, age, sex,
ward/OPD, hospital number, any previous sample number. Precise information
should be given regarding type of specimen, any fixative used, relevant clinical
information and any previous treatment. A written procedure must be in place
to handle specimens that are received without adequate information on the
request form.

High risk specimens should be clearly marked with biohazard stickers or labels.

The specimen after checking all labels should be given a lab identification
number. The laboratory identifier may be generated manually or electronically
and may be numeric or alphanumeric and may also be bar coded.

Criteria for the rejection of specimens:

z Unlabeled slides, slides labeled with nonpermanent writing utensils or paper

labels and broken slides.
z Mismatched specimens and requisition forms
z Specimen without accompanying requisition form

22.5 STORAGE OF SPECIMENS

Samples should be immediately prepared from the specimen. Record the date
of preparation on the specimen container and refrigerate any remaining
specimen. Specimen can be stored for one week before disposal. Ideally, samples
need to be kept until the specimen is reported by the cytopathologist. The extra
sample maybe required for any special tests to aid in the diagnosis.

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 MODULE Cytology : Specimen Collection & Storage

Histology and Cytology

INTEXT QUESTIONS 22.1

1. The field of diagnostic medicine that deals with individual cells is ...............
2. ............... must be used while treating unfixed specimens to prevent
transmission of infection.
Notes 3. Specimens should be transported to the laboratory as early as possible in
............... containers
4. All patients slides and samples should be labeled with ............... & ...............
5. ............... should never be transported with fluid specimens
6. High risk specimens should be clearly marked with ...............
7. Specimens can be stored for ............... before disposal
8. Samples should be stored until they are ...............

WHAT HAVE YOU LEARNT

z Cytology deals with the study of individual cells or tissue fragments
z Quality of cytodiagnosis depends on quality of preparation of the material
z Universal precautions must be followed while handling specimens
z Specimens should be sent to laboratory as early as possible in suitable
container that prevent breakage
z Lids should be properly secured to prevent leakages
z All specimens should be properly labeled with patients name and number
z Needles should never be transported with fluid specimens
z Specimen should be accompanied by filled requisition form
z High risk specimens should be clearly marked with biohazards stickers or
labels
z Samples should be stored until it is reported by pathologists

TERMINAL QUESTIONS
1. Define cytology.

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2. Give examples of samples on which cytology can be performed. Histology and Cytology

3. Enumerate few precautions to be taken while handling cytology specimens.

4. Enumerate the points to be kept in mind while transporting and receiving
cytology specimens.

ANSWERS TO INTEXT QUESTIONS Notes

22.1
1. Cytology
2. Universal precautions
3. Suitable
4. Patients name and Number
5. Needles
6. Biohazard stickers or labels
7. One week
8. Reported

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 MODULE Cytomorphology

Histology and Cytology

28
Notes
CYTOMORPHOLOGY

28.1 INTRODUCTION
Light microscopic examination of stained cells in smears is the method of choice
of diagnostic cytology. It allows classification of most normal cells as to type
and tissue of origin. It also allows the recognition of cell changes caused by
disease processes.

OBJECTIVES
After reading this lesson, you will be able to:
z recognize and classify cells
z identify features cell response to injury
z recognize features of tumors, especially malignancy.

28.2 GENERAL GUIDELINES

The study of cells in smears should take place at several levels:
z A rapid review of the smear with a 10× objective provides information on
the makeup of the sample and its cell content. This preliminary review will
tell the observer whether the smear is appropriately fixed and stained and
will provide initial information on its composition. Smears containing only
blood or no cells at all are usually considered inadequate, with some very
rare exceptions.
z If the smear contains cells other then blood cells, it should be examined
with care. A careful review of the material or screening of smears with a
10× objective is usually required to identify abnormal cells that may be few

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Cytomorphology MODULE
in number. Screening is mandatory in cancer detection samples from “well” Histology and Cytology
patients. A microscope stage should be utilized.
z The screening of the smear should lead to the preliminary assessment of
the sample and answer the following questions: (1) Does the cell population
correspond to the organ of origin? (2) If the answer is positive, the next
question pertains to the status of the cell population: (a) is it normal? (b)
does it show nonspecific abnormalities of little consequence to the patient?
Notes
or (c) Does it show abnormalities pertaining to a recognizable disease state
that can be identified.

28.3 CELL CLASSIFICATION

In general, the derivation, type of cells, and sometimes their function, are
reflected in the cytoplasm, whereas the nucleus offers information on the status
of the DNA, which is of particular value in the diagnosis of cancer. Some cells
that lack distinct cytoplasmic or nuclear features may be very difficult to classify.
For all practical purposes, the cells encountered in cytologic samples are of
epithelial and nonepithelial origin. In tissue sections, the cells are often cut “on
edge” and are seen in profiles. In cytologic preparations, the cells are whole and
are generally flattened on a glass slide, usually affording a much better analysis
of the cell components.

Epithelial Cells
An epithelium (plural: epithelia) is a tissue lining the surfaces of organs or
forming glands and gland-like structures. Similar epithelia may occur in various
organs and organ systems. There are four principal groups of epithelia: (1)
squamous epithelia, synonymous with protective function; (2) glandular epithelia
with secretory functions; (3) ciliated epithelia; and (4) the mesothelia.

Squamous Epithelium
The squamous epithelium is a multilayered epithelium that lines the surfaces of
organs that are in direct contact with the external environment. The growth of
the squamous epithelium is in the direction of the surface, that is, the cells move
from the basal layer, to parabasal layers, to intermediate layers, to superficial
layers. The most superficial cells are cast off. As the cells transit from the basal
to the more superficial layers, they are programmed to gradually increase the size
of their cytoplasm. The process of cytoplasmic maturation is accompanied by
nuclear changes. The nuclei of the basal, parabasal, and intermediate layers of
squamous cells appears as spherical, open (vesicular) structures, measuring
approximately 8 µm in diameter. As the cells transit from the intermediate to

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Histology and Cytology superficial layers, their nuclei shrink and become condensed (nuclear pyknosis).
In cytology, these cells tend to be flat, polygonal, and sharply demarcated, and
they vary in size according to the layer of origin. The smallest cells, measuring
about 10 µm in diameter, are the basal cells, which are very rarely seen in normal
states. Parabasal cells, derived from the parabasal layers, are somewhat larger,
measuring from 10 to 15 µm in diameter. Intermediate cells, derived from the
intermediate layers, are still larger, measuring from 15 to 40 µm in diameter. The
Notes
superficial cells are the largest, measuring from 40 to 60 µm in diameter.

Epithelia with Secretory Function

These epithelia are found mainly in organs with secretory functions and
exchanges with the external environment, such as food intake, principally in the
digestive tract and associated glands. On cytology, the secretory cells are
cuboidal or columnar in shape, averaging from 10 to 20 µm in length and 10
µm in width. Their cytoplasm is transparent because of accumulation of products
of secretion, usually mucus. Secretory cells are often polarized, that is, they
display one flat surface facing the lumen of the organ.

Mesothelia
Organs contained within body cavities, such as the lung, the heart, and the
intestine, are all enclosed within protective sacs lined by specialized epithelia
of mesodermal origin. These sacs, known as the pericardium for the heart,
pleural cavity for the lungs, and peritoneal cavity for the intestine, are lined by
an epithelium composed of a single layer of flat cells, known as mesothelial cells.
Under normal circumstances, the sacs are filled with only a thin layer of fluid
that facilitates the gliding of the two surfaces of mesothelial cells against each
other. On cytology, mesothelial cells may form sheets or clusters, in which the
adjacent, flattened surfaces of the cells are separated from each other by clear
gaps (“windows”) filled by microvilli.

Nonepithelial Cells
Endothelial Cells: they line the intima of blood vessels and have many
similarities with mesothelial cells but are very rarely observed in diagnostic
cytology.

The Immune Cell System: Consist of T & B Lymphocytes, macrophages and

plasma cells. Many benign and malignant conditions involving proliferation of
these cells can present for cytological evaluation. (Leukemias, lymphomas,
multiple myeloma).

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Histology and Cytology

INTEXT QUESTIONS 28.1

1. ....................... is a tissue lining the surfaces of organs or forming glands
and gland-like structures
2. ....................... is a multilayered epithelium that lines the surfaces of organs
that are in direct contact with the external environment Notes
3. ....................... are found mainly in organs of the digestive tract and
associated glands
4. The pericardium, pleural cavity and peritoneal cavity, are lined by
.......................
5. ....................... Cells line the intima of blood vessels

WHAT HAVE YOU LEARNT

z An epithelium is a tissue lining the surfaces of organs or forming glands
and gland-like structures
z There are four principal groups of epithelia: (1) squamous epithelia (2)
glandular epithelia with secretory functions; (3) ciliated epithelia; and (4)
the mesothelia
z The squamous epithelium is a multilayered epithelium that lines the
surfaces of organs that are in direct contact with the external environment
z The nuclei of the basal, parabasal, and intermediate layers of squamous cells
appears as spherical, open structures, measuring approximately 8 µm in
diameter
z The smallest cells, measuring about 10 µm in diameter, are the basal cells,
which are very rarely seen in normal states
z Parabasal cells, derived from the parabasal layers, measure from 10 to 15
µm in diameter
z Intermediate cells, derived from the intermediate layers, measure 15 to 40
µm in diameter.
z The superficial cells are the largest, measuring from 40 to 60 µm in diameter
z Epithelia are found mainly in organs with secretory functions and exchanges
with the external environment, such as food intake, principally in the
digestive tract and associated glands

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 MODULE Cytomorphology

Histology and Cytology z On cytology, the secretory cells are cuboidal or columnar in shape,
averaging from 10 to 20 µm in length and 10 µm in width. Their cytoplasm
is transparent because of accumulation of products of secretion, usually
mucus.
z The pericardium, pleural and peritoneal cavity, are lined by an epithelium
composed of a single layer of flat cells, known as mesothelial cells
Notes z In cytology, mesothelial cells form sheets or clusters, in which the adjacent,
flattened surfaces of the cells are separated from each other by clear gaps
(“windows”) filled by microvilli
z Endothelial Cells line the intima of blood vessels

TERMINAL QUESTIONS
1. What are the general guidelines while assessing a cytological smear?
2. Enumerate the different types of cells which can be encountered while
examining a cytologic smear.
3. What are the different forms of squamous cells seen in cytology?

ANSWERS TO INTEXT QUESTIONS

28.1
1. Epithelium
2. Squamous epithelium
3. Epithelia
4. Mesothelial cells
5. Endothelial

168 HISTOLOGY AND CYTOLOGY

 MODULE Metachromatic Staining

Histology and Cytology

12
Notes
METACHROMATIC STAINING

12.1 INTRODUCTION
There are certain basic dyes belonging to aniline group that will differentiate
particular tissue components by giving them a different color to that of original
dye. The phenomenon is known as metachromasia.

OBJECTIVES
After reading this lesson, you will be able to:
z define metachromasia
z describe the process metachromasia
z know common metachromatic dyes
z describe the factors enhancing metachromasia.

The tissue element reacting in this manner are said to be exhibiting metachromasia.
z The generally accepted explanation of this phenomenon is that change in
color is due to polymerization.
z Sulfated substances are highly metachromatic e.g. Mast cell granules.
z Mast cells contain Heparin which is highly sulfated.

Some of the common metachromatic dyes are:

z Methylene blue, Methyl violent
z Thionin, Crystal violet
z Toluidine blue

12.2 METACHROMASIA
Metachromasia takes place when certain negatively charged groups on the tissue
react with cationic dyes. On polymerization the original colour of the dye
changes to another colour (eg mast cell stain pink with toluidine blue).

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Metachromatic Staining MODULE
Thionin and toluidine blue dyes are commonly used for quick staining of frozen Histology and Cytology
selection using their metachromatic property to stain nucleus and cytoplasm
differently.
Metachromasia is enhanced when intermolecular distances are reduced.
Factors which enhance metachromasia are
1. Increasing concentration of dye. Notes
2. Decreasing temperature.
3. pH
4. Water a polar solvent, contributes to the efficiency of van der Waal’s forces
by which the molecules are held together.
In tissues, where there is a high concentration of anions e.g. in sulphated
mucopolysaccharides, the cationic dye molecules may be held in such close
proximity to one another that van der Waal’s forces can exert their influence and
cause the dye to polymerize. Consequently the colour changes from blue to red.
Tissue components often demonstrated by metachromatic stains:
z Amyloid material, Mast cell granules
z Mucin Cartilage
Amyloid Stain -Various stains are used to demonstrate amyloid

12.3 CRYSTAL VIOLET STAIN FOR AMYLOID

Aim: To demonstrate amyloid in tissue sections.

Principle: Amyloid (a glycoprotein) exhibits metachromasia in tissue sections

when stained with crystal violet and other cationic dyes.

Control: ositive control.

Reagents
Crystal violet solution

Stock solution

z Crystal violet 14gm

z 95% alcohol 100ml
Working solution

z Stock solution 10ml

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 MODULE Metachromatic Staining

Histology and Cytology z Distilled water 300ml

z Concentrated hydrochloric acid 1ml

Procedure
z Deparaffinize and bring the sections to water.
z Put working crystal violet solution for 1 to 2 minutes and check under
Notes microscope.
z Rinse in tap water.
z Mount in water or in water soluble media.
z Put on the coverslip seal the edges with nail polish (Do not let it dry.)

Result
z Amyloid purple violet
z Other tissues blue

12.4 CONGO-RED STAIN FOR AMYLOID

Aim: To demontrate amyloid in tissues.
Principle: Diazo dye attaches itself to amyloid fibrils. The union is affected by
H bonds between the OH groups of amyloid and amino side groups of the dye.
Congo red dye forms non-polar hydrogen bonds with amyloid. The green
birefringence of congo red stained amyloid by polarized light is considered
diagnostic of amyloid.
Control: Known positive tissue

Reagents
Congo red solution
z Congo red 1.0gm
z Distilled water 100ml
Saturated solution of Lithium Carbonate
z Lithium carbonate 1.3gm
z Distilled water 100ml

Procedure
z Bring section to water.

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Metachromatic Staining MODULE
z Pour congo red solution for 20 minutes. Histology and Cytology

z Pour off the solution and cover the slide with lithium carbonate for 1.5
minutes to differentiate.
z Wash with water.
z Counter-stain with hematoxyline for 5 minutes.
z Differentiate with 1% acid alcohol. Notes
z Wash in running tap water.
z Dehydrate, clear in xylene and mount in DPX.

Result
z Amyloid bright red which gives apple green birefringence in
polarized light.
z Nuclei blue
z Other structures unstained to yellow

Notes
1. Sections must be cut at 8 to 10 microns for birefringence
2. Solution must be filtered through glass wool, not paper filters for birefringence
to occur
3. Tissue fixed in solutions other than formalin may display false positive
birefringence

INTEXT QUESTIONS 12.1

1. .................... & .................... dyes are commonly used for quick staining of
frozen section
2. Metachromasia is enhanced when .................... are reduced
3. Tissues demonstrated by metachromatic stain are ...................., ....................
& ....................
4. .................... & .................... alcohol is used as fixation in crystal violet stain
5. ..................... and ..................... are used for demonstrating amyloid in
tissues

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 MODULE Metachromatic Staining

Histology and Cytology

WHAT HAVE YOU LEARNT

z Basic dye belonging to aniline group differentiates particular tissue
components by staining them a different colour to that of original dye by
phenomenon known as metachromasia
z Metachromasia occurs due to polymerization
Notes z Methylene blue, methyl violet, thionin, crystal violet and toluidine blue are
the metachromatic dyes
z Thionin and toluidine blue dyes are commonly used for quick staining of
frozen section
z Metachromasia is enhanced when intermolecular distance are reduced
z Increasing concentration of dye, decreasing temperature, pH, water enhance
metachromasia
z Amyloid material, mast cell granules, and mucin cartilages are demonstrated
by metachromatic stains
z Crystal violet, cango red stain are used for demonstrating amyloids
z In metachromatic stain amyloid appear pink and the surrounding tissues
stain purple
z Crystal violet stain and congo-red stain are used to demonstrate amyloid
in tissues.

TERMINAL QUESTIONS
1. What are the dyes used in metachromasia?
2. What are the factors which enhance metachromasia?
3. Explain the procedure of metachromasia.
4. Explain briefly stains used for demonstrating amyloid in tissues.

ANSWERS TO INTEXT QUESTIONS

12.1
1. Thionin and toluidine
2. Intermolecular distance
3. Amyloid material, Mast cell granules & Mucin Cartilage
4. Carnoy’s and absolute
5. Crystal violet, congo – red stain.

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Quality Control in Cytology MODULE
Histology and Cytology

27
Notes
QUALITY CONTROL IN
CYTOLOGY

27.1 INTRODUCTION
Cytopathologists are concerned about and committed to quality assurance and
quality control in their laboratories. These practices include, among others, the
use of intralaboratory and extradepartmental consultations, case reviews,
correlation of cytologic and histopathologic specimens and review of completed
diagnostic reports.

OBJECTIVES
After reading this lesson, you will be able to:
z describe Quality control in cytology
z explain various methods of quality control in cytology.

27.2 QUALITY ASSURANCE MEASURES

Cytopathology is a practice of medicine and represents a medical consultation,
in both gynecologic and nongynecologic anatomic sites. The basic principles of
quality assurance apply to all types of cytologic specimens. The following
represents several minimum quality assurance measures.
1. Laboratory Directors
The laboratory should be directed by a legally qualified physician with a
specialist qualification in pathology, including special training and expertise
in cytopathology. The director or designated medical professional is
responsible for proper performance and reporting of all tests done in the
cytopathology laboratory. The director or designated cytopathologist should

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Histology and Cytology

be physically present in the laboratory to direct the staff, be available for
consultations, review all reactive and abnormal gynecologic cytology
samples, review fine needle aspiration samples, and review all nongynecologic
samples.
2. Cytotechnologists
A suitably qualified person should be recruited for this position.
Notes 3. Physical Laboratory Facilities
The laboratory should be clean, well lighted, adequately ventilated, and
functionally arranged so as to minimize problems in specimen handling,
evaluation, and reporting. The area for specimen preparation and handling
should be separate from the area where specimens are evaluated and
reported. Formaldehyde and xylene (if in use) should be carefully monitored
due to the possible presence of hazardous vapor concentrations.
4. Safety Precautions
Laboratory personnel must be protected against hazards (chemical, electric,
fire, infections, or others) by using well-ventilated hoods and biologic safety
hoods for handling potentially infectious material. Fire precautions should
be posted and tested.
5. Equipment
An adequate number of binocular microscopes of good quality and proper
working order must be available. Laboratory instruments and equipment
should be under periodic maintenance to monitor and ensure malfunctions
do not adversely affect analytical results.
6. Specimen Collection
Cytologic specimens should be accepted and examined only if requested
by a licensed medical practitioner and collected in accordance with
instructions regarding recommended collection techniques. The cytopathology
laboratory should inform the originator of the sample if the specimens are
“unsatisfactory” and detail adequacy qualifiers such as presence or absence
of a transformation zone component or obscuring factors in “satisfactory
samples”.
7. Preparation, Fixation, and Staining Procedures
The specimens must be identified with the patient’s name and/ or a unique
identifier and must be accompanied by a requisition form with the
requesting physician’s name, address, date of specimen collection, specimen
source, and appropriate clinical information about the patient. When the
specimen arrives in the laboratory the laboratory staff affix an accession
number or bar code label on each slide for further identification. The

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laboratory should have written criteria for rejecting specimens. Fixation Histology and Cytology
while the specimen is still wet is recommended for conventional cell
samples. The Papanicolaou staining procedure is strongly suggested for
most cytologic samples, unless additional staining procedures are warranted.
Staining solutions and chemicals used in the cytopathology laboratory
should be labeled with the time of preparation, purchase, or both. Staining
solutions should be filtered regularly to avoid contamination and should be
covered when not in use. Effective measures to prevent cross-contamination Notes
between gynecologic and nongynecologic specimens during the staining
process must be used.
8. Slide Evaluation Workload
Regulations as to the number of specimens a cytotechnologist may evaluate
in a 24-hour period are currently set at 100 slides per an 8-hour day. This
regulation may not do justice to the various conditions that influence the
quality of the slide evaluation performance. The percentage of atypical cases
evaluated versus the percentage of negative cases in varying populations
as well as screening of nongynecologic specimens should be considered
when workloads are established. This regulation ensures that the number
and type of cytologic samples evaluated do not, through fatigue, adversely
affect the cytotechnologist’s performance.
9. Cytologic Terminology
The vaginal/ectocervical/endocervical cytology sample should be interpreted
preferably by using the Bethesda System. The nongynecologic material
should be interpreted in medical terms.
10. Laboratory Records, Logs, and Files
Each specimen should be recorded and a sequential accession number
assigned together with the name of the patient and the originator of the
sample. Test records must be retained for at least 5-10 years. The negative
gynecologic cell samples should be retained on file for a minimum of 5 years
and negative fine needle aspirates for 10 years or indefinitely if they exhibit
abnormal features. The modern cytopathology laboratory should use a
computerized file system.

INTEXT QUESTIONS 27.1

1. For conventional cell samples .................. is recommended while the
specimen is wet.
2. .................. staining procedure is suggested for most cytologic samples

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 MODULE Quality Control in Cytology

Histology and Cytology 3. cytotechnologist may evaluate in a 24-hour period .................. number of
slides per an 8-hour day
4. The vaginal cytology sample should be interpreted using ..................
System.
5. Test records must be retained for at least .................. years
6. Negative fine needle aspirates should be retained for .................. years
Notes

WHAT HAVE YOU LEARNT

z Quality control practices include, the use of intralaboratory and
extradepartmental consultations, case reviews, correlation of cytologic and
histopathologic specimens and review of completed diagnostic reports.
z The laboratory should be directed by a legally qualified physician with a
specialist qualification in pathology, including special training and expertise
in cytopathology
z A suitably qualified person should be recruited as cytotechnologists
z The laboratory should be clean, well lighted, adequately ventilated, and
functionally arranged so as to minimize problems in specimen handling,
evaluation, and reporting
z Laboratory personnel must be protected against hazards
z An adequate number of binocular microscopes of good quality and proper
working order must be available
z Cytologic specimens should be accepted and examined only if requested
by a licensed medical practitioner and collected in accordance with
instructions regarding recommended collection techniques
z The specimen as it arrives in the laboratory should be given an accession
number or bar code label on each slide for further identification.
z The laboratory should have written criteria for rejecting specimens.
z Fixation while the specimen is still wet is recommended for conventional
cell samples.
z The Papanicolaou staining procedure is strongly suggested for most
cytologic samples, unless additional staining procedures are warranted.
z Staining solutions and chemicals used in the cytopathology laboratory
should be labeled with the time of preparation, purchase, or both

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z Regulations as to the number of specimens a cytotechnologist may evaluate Histology and Cytology
in a 24-hour period are currently set at 100 slides per an 8-hour day
z The vaginal/ectocervical/endocervical cytology sample should be interpreted
preferably by using the Bethesda System.
z The nongynecologic material should be interpreted in medical terms.
z Test records must be retained for at least 5-10 years.
Notes
z The negative gynecologic cell samples should be retained on file for a
minimum of 5 years and negative fine needle aspirates for 10 years

TERMINAL QUESTIONS
1. Write briefly about objective of quality assurance in cytopathology.
2. Enumerate the various measures of quality assurance.
3. How long do you need to maintain the records of cytopathology specimens?

ANSWERS TO INTEXT QUESTIONS

27.1
1. Fixation
2. Papanicolaou
3. 100
4. Bethesda
5. 5-10
6. 10

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Hematoxylin and Eosin Staining MODULE
Histology and Cytology

10
Notes
HEMATOXYLIN AND EOSIN
STAINING

10.1 INTRODUCTION
The sections, as they are prepared, are colourless and different components
cannot be appreciated. Staining them by different coloured dyes, having
affinities of specific components of tissues, makes identification and study of
their morphology possible. Hematoxylin and Eosin (H&E) is the most frequently
used stain in histology.

OBJECTIVES
After reading this lesson, you will be able to:
z describe Hematoxylin and its preparation
z describe the properties of Hematoxylin
z explain Eosin and its preparation
z describe the method of staining.

10.2 HEMATOXYLIN
It is extracted from the bark of a tree”, hematoxylom campechianum”. The
hematoxylin which we buy is extracted from this bloodwood tree. To obtain the
bark of freshly logged tree is chipped off, then boil the chips in water. An orange
red solution is obtained, which turns yellow, then black on cooling. The water
is evaporated leaving crude hematoxylin. Further purification is done.

Solutions of the dye should be oxidized to retain its staining ability longer. The
dye may be oxidized by exposure to the natural light for 3-4 months. Chemical

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 MODULE Hematoxylin and Eosin Staining

Histology and Cytology oxidation is achieved by using either sodium iodate or mercuric oxide. The
chemical oxidation converts the dye almost instantaneously but the product does
not have shelf life. Sodium iodate is most commonly used oxidizing agent (0.2
gm oxidizes 1.0 gm hematoxylin).

Hematoxylin is neither a dye nor it has coloring properties. For nuclear staining
it is necessary to oxidize the hematoxylin to hematin which is a weak anionic
Notes purple dye. Anionic hematin will have no affinity for the nucleic acids of nuclei.
Hence a metallic salt or mordant is combined with hematoxylin so that a positive
charge to the dye is obtained by virtue of the metal action. Thus the cationic dye
–metal complex will bind to the anionic nuclear chromatin. Various mordants
are ammonium or potassium alum ferric salt, chrom alum and phosphotungstic
acid. The tissue component most frequently demonstrated is nuclear chromatin
using an alum mordant in the H&E staining method.

The combination of hematoxylin and mordant is called a hematoxylin lake. The

aluminium lake formed with ammonium alum is particularly useful for staining
nuclei. Hematoxylin recipes using these mordants are called alum hematoxylin.

10.3 PROPERTIES OF HEMATOXYLIN

1. Hematoxylin has no staining property
2. Hematin with mordant such as ammonium or potassium alum forms lake
which functions as cationic dye and stains anionic tissue components.
3. Hematin in an aqueous solution can be acidic or an alkaline dye depending
on pH.
4. Hematin has affinity for several tissues with an appropriate mordant.
Progessive staining - When tissue is left in the stain just long enough to reach
the proper end point. The slides have to be examined at different interval to find
out when the staining is optimum.

Regressive staining - In this method the tissue is overstained and then destained
(differentiate) until the proper endpoint is reached.

Harris hematoxylin is a regressive stain; the overstaining is removed by acid -

alcohol. The removal of this excess dye is called differentiation.

The hematoxylin alum gives a reddish hue to the tissues because of acidic pH.
To convert this colour to the final blue, alkaline pH is required. This process is
called “blueing”. It is done either by tap water or by ammonium hydroxide.

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Hematoxylin and Eosin Staining MODULE
Preparation of Harris’s hematoxylin Histology and Cytology

Ingredients :
Hematoxylin 5gm
Absolute alcohol 50ml
Ammonium alum 100gm
Distilled water 1000ml Notes
Mercuric oxide 2.5gm
Glacial acetic acid 40ml
Method - Dissolve the hematoxylin in absolute alcohol and ammonium alum
in hot water. Mix the two solutions and heat to boiling. Remove from flame, and
add mercuric oxide and cool rapidly. Glacial acetic acid if added gives brisk
nuclear staining, but life of the solution is reduced. Hence if acetic acid is to be
added, it should be added in working solution.

Preparation of Mayer’s hematoxylin

Ingredients :
Hematoxylin 1.0gm
Distilled water 1000ml
Ammonium alum 50gm
Sodium iodate 0.2gm
Citric acid (reduces pH) 1.0gm
Chloral hydrate (preservative) 50gm
Method - Hematoxylin is dissolved in distilled water using gentle heat. Then
alum is added and dissolved. Then sodium iodate, citric acid and chloral hydrate
are added respectively.

10.4 EOSIN
Eosin is used as the counterstain that stains the cytoplasm rose coloured. The
intensity of the eosin is individual choice. The most widely used eosin is “eosin
Y”. The “Y” stands for yellowish. It is available in either water soluble or alcohol
soluble form. Most laboratories use the water soluble form of eosin Y in an
alcohol-water solution which is described here.
Eosin Y (water soluble) 1.0gm
Distilled water 80ml

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Histology and Cytology 95% alcohol 320ml

Glacial acetic acid 0.4ml
Preparation - Dissolve eosin in water and then add this to 95% alcohol (one
part eosin solution with 4 parts alcohol). To the final mixture add a few drops
of acetic acid (0.4ml). The acetic acid increases the staining intensity of eosin.
When ready to use, the stain should be cloudy; if clear, add a few drops of the
Notes acetic acid. The solution should be standardized by staining the control slides.

10.5 METHOD OF STAINING

1. Deparaffinize sections in xylene, 10-20 minutes. Filter Hematoxylin.
2. Rehydrate sections:
100% alcohol for 1-2 minutes
95% alcohol for 1-2 minutes
3. Rinse in tap water
4. Rinse in distilled water
5. Stain with Hematoxylin for 3-5 minutes
6. Wash in tap water
7. Differentiate section with 1% HCl in 70% alcohol 1-2 dips and check under
microscope. If necessary, return slides to HCl for further differentiation.
8. Wash slides in running tape water for 15 minutes
9. Stain slides in Eosin for 1-4 minutes
10. Dehydration and Differentiation:
95% alcohol 5-6 dips
100% alcohol 5-6 dips
11. Clear slides in xylene 2 times
12. Mount slides with mounting media (Permount or DPX)

Note
1. At no stage of staining the section should be dry
2. H&E is a regressive stain in which a tissue is over-stained and then excess
dye is removed to obtain desired intensity of stain
3. Filter Hematoxylin each time before staining
4. Change most of alcohol and xylene each time before staining

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Hematoxylin and Eosin Staining MODULE
Histology and Cytology

INTEXT QUESTIONS 10.1

1. Most commonly used stain in histology is .....................
2. ..................... is the most commonly used oxidising agent
3. Tissue component commonly demonstrated is ..................... by hematoxylin.
Notes
4. Combination of hematoxylin and mordant is called .....................
5. In H & E staining ..................... staining technique is followed
6. Process of removing excess dye is called .....................
7. Converting red hue to blue colour by use of alkaline pH is called ..................
8. ..................... is used as counter stain which stains the cytoplasm rose colour

WHAT HAVE YOU LEARNT

z Staining with different coloured dyes makes identification and study of
morphology possible
z Haemotoxylin and Eosin is the most commonly used stain in histology
z Sodium iodate is most commonly used oxidising agent
z Nuclear chromatin is usally demonstrated using H & E staining method
z Combination of hematoxylin & mordant is called hematoxylin lake
z Haematoxylin has no staining property, hematin has affinity for several
tissues with an appropriate mordant
z Regressive staining is used in H & E staining
z The process of removing excess dye is called differentiation
z Process of converting red colour of tissue using alkaline pH to blue colour
is called blueing

TERMINAL QUESTIONS
1. Explain the properties of hematoxylin
2. Explain preparation of hematoxylin and Eosin
3. Describe briefly H & E staining

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Histology and Cytology

ANSWERS TO INTEXT QUESTIONS

10.1
1. Hematoxylin & Eosin
2. Sodium iodate
Notes
3. Nuclear chromatin
4. Hematoxylin lake
5. Regressive
6. Differentiation
7. Blueing
8. Eosin

64 HISTOLOGY AND CYTOLOGY

Hormonal Assessment MODULE
Histology and Cytology

29
Notes
HORMONAL ASSESSMENT

29.1 INTRODUCTION
The established approach to the evaluation of ovarian function and endocrine
disorders in the woman is based on serial biochemical analyses of hormones,
such as estrogen, progesterone, luteinizing hormones and their metabolites. In
women who suffer from menstrual disorders and abnormalities of the ovarian
cycle, the biochemical analyses can be effectively supplemented by the old-
fashioned endometrial biopsies, or studies of endocervical mucus. In addition,
the cervicovaginal smear may sometimes provide useful information and has the
advantage of being easy to obtain, rapidly evaluated, and inexpensive. The
cytologic approach is particularly valuable if laboratories specializing in
endocrine analysis are not readily available. The principle of the cytologic
hormonal analysis is simple. The degree of maturation of the squamous
epithelium of the female genital tract depends on steroid hormones, mainly
estrogen.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the basics of hormonal assessment

z identify the features of squamous cell maturation.

29.2 HORMONAL ASSESSMENT

Naturally occurring estrogen, or the parenteral administration of estrogen or its
natural or synthetic substitutes in adequate amounts, produces a rapid and
complete maturation of the normal squamous epithelium of the female genital
tract with a resulting preponderance of mature superficial squamous cells in
smears. The effect takes place regardless of the prior hormonal status, except

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Histology and Cytology during pregnancy. Conversely, complete atrophy of the squamous epithelium of
the vagina and cervix may be equated with complete absence of estrogenic
activity. However, there are no reliable data linking intermediate degrees of
maturation of the squamous epithelium with the action of a specific hormone or
hormones.
Evaluation of the endocrine status of a menstruating woman during the
childbearing age belongs among the most difficult tasks in diagnostic cytology.
Notes
There is considerable variation in the smear patterns from one patient to another,
even if matched for age and menstrual history.

Several conditions must be fulfilled before a successful hormonal evaluation of

the squamous epithelium may be undertaken.

z There must be absence of inflammation or cytolysis.

z There must be no recent medication, either topical or systemic, especially
with compounds known to affect the squamous epithelium of the lower
genital tract.
z There must be no history of radiotherapy or recent surgery to the vagina
or cervix.
z An adequate baseline investigation must have been performed in menstruating
women. This should include daily smears during at least one and preferably
two complete cycles, or their chronologic equivalent. In nonmenstruating
patients, two or three smears may suffice.
z The smears should be obtained from the proximal portion of the lateral wall
of the vagina, care being taken to avoid contamination with material from
the adjacent cervix.

The Karyopyknotic Index (KI)

The karyopyknotic index expresses the percentile relationship of superficial
squamous cells with pyknotic nuclei to all mature squamous cells. Usually, 200
to 400 consecutive cells in three or four different fields on the smear are
evaluated. The peak of KI usually coincides with the time of ovulation and was
estimated at 50% to 85% of total cells.

The Eosinophilic Index (EI)

The eosinophilic index expresses the percentile relationship of mature squamous
cells with eosinophilic cytoplasm to all mature squamous cells, regardless of the
status of the nucleus. In a normal menstruating woman, the peak of EI coincides
with the peak of KI and may reach 50% to 75% at the time of ovulation.

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The Maturation Index (MI) Histology and Cytology

The maturation index expresses the maturation of the squamous epithelium as

a percentile relationship of parabasal cells to intermediate cells to superficial
cells. The count should be performed on single cells. For example, in a normal
menstruating woman at the time of ovulation, an MI of 0:35:65 would indicate
that the smear contained no parabasal cells, 35% of intermediate cells, and 65%
of superficial cells.
Notes
Other Indices
The folded-cell index represents the relationship of mature superficial or
intermediate squamous cells with folded cytoplasm to all mature squamous
cells. The crowded-cell index represents the relationship of mature squamous
cells lying in clusters of four or more cells to all mature squamous cells.

Alternative Ways of Reporting Hormonal Status

It has been a common practice to base the evaluation of the maturation of the
squamous epithelium on an overall visual impression gained during the routine
screening of smears. This simplest of methods has not failed in revealing major
abnormalities of smear patterns. By comparing the current smear pattern with
original baseline smears, a good appreciation of changes in smear pattern may
be gained. Small variations in smear pattern have no diagnostic meaning but may
strongly influence the indices and thus give a false impression of hormonal
“effects.” The reporting of smears based on this overall visual impression is
always given in reference to age, menstrual history, and possible clinical
significance. Some examples follow:
Patient age 35: “Midcycle smear pattern—consistent with functioning ovaries.”
Patient age 52: “Absence of maturation of squamous cells consistent with
menopause.”
Patient age 25: “Absence of maturation of squamous cells—abnormal for age.”
Patient age 60: “High level of maturation of squamous cells not consistent with
clinical menopause. It is assumed that this patient is not receiving estrogens or
other drugs that may account for this smear pattern.”

29.3 DETERMINATION OF THE TIME OF OVULATION

FROM CERVICOVAGINAL SMEARS
A precise determination of the time of the ovulation is important in artificial
insemination and in in-vitro fertilization. The use of the cervicovaginal smears

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Histology and Cytology to establish the time of ovulation or the status of the endometrium has been of
limited reliability. It is recommended that cytologic methods for estimation of
ovulation or status of the endometrium be supplemented by other procedures,
such as temperature curves and endometrial biopsies. The examination of
endocervical mucus may also be of assistance. Cyclic changes in the
physicochemical properties of the cervical mucus have been known for a great
many years. Prior to ovulation, the mucus tends to be viscous and when placed
Notes on a glass slide, form crystalline, fern-like structures, whereas at the time of and
after ovulation, the mucus is more liquid and does not crystallize.

Cytologic evaluation for menstrual abnormalities

1. Cytologic hormonal evaluation may be of assistance in the evaluation of
amenorrhea (cessation of menses), in women who have never menstruated
(primary amenorrhea) or who stopped menstruating at a young age after a
period of normal menses (secondary amenorrhea).
2. Effects of Castration: The effects of castration, either surgical or radiation
induced, may be conveniently followed by vaginal smears.
3. Ovarian Tumors: Certain ovarian tumors, particularly the granulosa cell
tumors and the thecomas, may produce estrogen-like substances
4. Precocious Puberty in Girls

INTEXT QUESTIONS 29.1

1. The degree of maturation of the squamous epithelium of the female genital
tract depends on .................... hormones.
2. .................... index expresses the percentile relationship of superficial
squamous cells with pyknotic nuclei to all mature squamous cells
3. .................... index expresses the percentile relationship of mature squamous
cells with eosinophilic cytoplasm to all mature squamous cells
4. .................... index expresses the maturation of the squamous epithelium as
a percentile relationship of parabasal cells to intermediate cells to superficial
cells
5. .................... index represents the relationship of mature superficial or
intermediate squamous cells with folded cytoplasm to all mature squamous
cells
6. .................... index represents the relationship of mature squamous cells
lying in clusters of four or more cells to all mature squamous cells

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Histology and Cytology

WHAT HAVE YOU LEARNT

z The evaluation of ovarian function and endocrine disorders in the woman
is based on serial biochemical analyses of hormones, such as estrogen,
progesterone, luteinizing hormones and their metabolites
z The degree of maturation of the squamous epithelium of the female genital Notes
tract depends on steroid hormones, mainly estrogen.
z The smears should be obtained from the proximal portion of the lateral wall
of the vagina
z The karyopyknotic index (KI) expresses the percentile relationship of
superficial squamous cells with pyknotic nuclei to all mature squamous
cells
z The peak of KI usually coincides with the time of ovulation and was
estimated at 50% to 85% of total cells.
z The eosinophilic index expresses the percentile relationship of mature
squamous cells with eosinophilic cytoplasm to all mature squamous cells,
regardless of the status of the nucleus
z In a normal menstruating woman, the peak of EI coincides with the peak
of KI and may reach 50% to 75% at the time of ovulation
z The maturation index expresses the maturation of the squamous epithelium
as a percentile relationship of parabasal cells to intermediate cells to
superficial cells
z The folded-cell index represents the relationship of mature superficial or
intermediate squamous cells with folded cytoplasm to all mature squamous
cells
z The crowded-cell index represents the relationship of mature squamous
cells lying in clusters of four or more cells to all mature squamous cells
z Cytologic hormonal evaluation may be of assistance in the evaluation of
amenorrhea

TERMINAL QUESTIONS
1. What are the conditions requiring cytologic hormonal assessment?
2. Enumerate the various methods of hormonal assessment on cytologic smears.
3. Enumerate the precautions required before taking a sample for hormonal
assessment of cytologic smears

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 MODULE Hormonal Assessment

Histology and Cytology

ANSWERS TO INTEXT QUESTIONS

29.1
1. Estrogen
2. Karyopyknotic index
Notes
3. Eosinophilic
4. Maturation
5. Folded-cell
6. Crowded-cell

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 MODULE Special Processing

Histology and Cytology

17
Notes
SPECIAL PROCESSING

17.1 INTRODUCTION
Some pathological specimens require special handling and need to be processed
in a different way to reach the final diagnosis. Examples include eyeball, bones
and bone marrow biopsy. The technical person needs to be aware of these special
specimens so that appropriate measures can be taken before the grossing
procedures are undertaken.

OBJECTIVES
After reading this lesson, you will be able to:
z explain the principle of special processing
z explain the different specimens requiring special processing
z learn how to do special processing procedures.

17.2 BONE
Normal human skeleton has two main types of bones: cortical or compact bone
which is hard, solid and very strong and forms shafts of long bones i.e. the femur
and tibia etc; and spongy or trabecular/ cancellous bone is found in the marrow
cavities and is a mesh of bone strands which is almost ideal weight bearing
structure particularly in the femoral head and vertebrae. The three major
components of bone are mineral, cells and an organic extra-cellular matrix i.e.
collagen fibers. The main bulk of bone is approximately 70% mineral and 30%
organic components by weight. Bone cells are relatively few as opposed to
marrow cells. The mineral of bone is mainly calcium and phosphate.
Techniques for the demonstration of bone and its components include:

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Special Processing MODULE
z For decalcified bone: frozen, paraffin, or celloidin sections, transmission Histology and Cytology
electron microscopy.
z For mineralized bone: frozen, plastic, scanning and transmission electron
microscopy.
In order to obtain satisfactory paraffin sections of bone, inorganic calcium must
be removed from the organic collagen matrix, calcified cartilage and surrounding
tissues. This is called decalcification and is carried out by chemical agents, either
Notes
with acids to form soluble calcium salts or with chelating agents that bind to
calcium ions. Any acid, however well buffered, can have damaging effects on
tissue staining. The problem increases with acidity of solution and duration of
decalcification period. It mostly affects the nuclei which fail to take up
hematoxylin and other basic dyes. These effects can be reduced by doing the
decalcification end point test, post-decalcification acid removal and adjustment
of the stain procedure.

17.3 DECALCIFYING AGENTS

Acids
Acid decalcifiers can be divided into two groups: strong (inorganic) and weak
(organic) acids.
Strong Inorganic acids: e.g. nitric and hydrochloric acids may be used as simple
aqueous solutions (5-10%). They decalcify rapidly but cause tissue swelling and
can seriously damage tissue stainability if used longer than 24-48 hours. Old
nitric acid is particularly damaging and should be replaced with fresh stock They
also damage tissue antigens for immunohistochemistry and enzymes may be
totally lost. They can be used for small needle biopsies to permit rapid diagnosis
within 24hrs. They can also be used for large or heavily mineralized bones with
decalcification progress being carefully monitored.
Aqueous Nitric acid, 5-10%
Nitric acid 5-10 ml
Distilled water To make 100ml
Formalin-nitric acid
Formaldehyde (37-40%) 10 ml
Distilled water 80 ml
Nitric acid 10 ml
Weak organic acids: e.g. fromic, acetic and picric acid. Of these three formic
acid is the only weak acid which is used in decalcification. Other two are used
as components of other fixatives. Formic acid solutions can be aqueous (5-10%),

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 MODULE Special Processing

Histology and Cytology buffered or combined with formalin. The formalin-10% formic acid mixture
fixes and decalcifies simultaneously and can be used for small biopsies. Formic
acid is suitable for most routine surgical specimens, particularly when
immunohistochemistry is needed. Decalcification is usually complete in 1-10
days and decalcification progress should be monitered by a decalcification end
point test.

Notes Aqueous formic acid

90% stock formic acid 5-10 ml
Distilled water To make 100 ml
Formic acid-formalin
90% stock formic acid 5-10 ml
Formaldehyde (37-40%) 5 ml
Distilled water To make 100 ml
Buffered formic acid
20% aqueous sodium citrate 65 ml
90% stock formic acid 35 ml

17.4 CHELATING AGENTS

The chelating agent used for decalcification is ethylene-diaminetetracetic acid
(EDTA). Although called an acid, it does not act like acids. EDTA will not bind
to calcium below pH 3 and is faster at pH 7-7.4. This is a very slow process that
does not damage tissues or their stainability, it also retains good antigen
preservation for immunohistochemistry or enzyme staining and electron
microscopy. The time required to totally decalcify dense cortical bone may be
6-8 weeks or longer although small bone spicules may be decalcified in less than
a week.
Formalin-EDTA
EDTA, disodium salt 5.5 g
Distilled water 90 ml
Formaldehyde (37-40% stock) 10 ml
Aqueous EDTA, pH 7.0-7.4
EDTA, disodium salt 250 g
Distilled water 1750 ml
If solution is cloudy, adjust to pH 7 with sodium hydroxide.

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Special Processing MODULE
Factors influencing the rate of decalcification Histology and Cytology

There are several factors influencing the rate of decalcification. The concentration
and volume of the active reagent, including the temperature at which the reaction
takes place, are important at all times. The more concentrated acids solutions
decalcify bone more rapidly but are more harmful to the tissue. The usuall
recommended ratio of volume of decalifying fluid to volume of tissue is 20:1
and the fluid should be changed several times during the decalcification
Notes
Process. Increased temperature accelerates decalcification, but it also increases
the tissue damage and loss of heat sensitive antigen and enzymes. Other factors
that contribute include the age of patient, type of bone, size of specimen and
solution agitation. Mature cortical bone decalcifies more slowly than immature
bone.

Treatment following decalcification

Acids can be removed from tissues or neutralized chemically after decalcification
is complete. It can be done by immersing the bone into either saturated lithium
carbonate solution or 5-10% aqueous sodium bicarbonate solution for several
hours. Many laboratories rinse the specimens with running tap water for a period
of time.

Eyeball
The eye should be placed in fixative as soon as practical after removal. Many
of the tissues, the retina in particular, are very sensitive to anoxia and the longer
you wait to fix the eye, the greater will be the artifacts, making interpretation
difficult.
If eyes arrive in formalin and have been fixed for 2 days, wash them in water
to remove the formalin (2 changes about 5 minutes each) and place them in
enough 50% ethanol to cover the eye. Let the eye equilibrate overnight. Change
the alcohol the next day and equilibrate for a second day. The eye should return
to a normal volume and should not be indented or shrunken. For sectioning the
eye it is best to wait 2 days with the eye in 50% ethanol.

INTEXT QUESTIONS 17.1

1. For sectioning of the eyes, eyes must be placed in .................. for atleast
..................
2. Removal of inorganic calcium from the matrix is called ..................

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Histology and Cytology 3. Examples of strong inorganic acids are .................., ..................
4. Examples of weak organic acids are .................., .................. & ..................
5. Chelating agent used for decalcification is ..................

Notes WHAT HAVE YOU LEARNT

z When eye balls placed in formalin are taken for sectioning, it is best to place
the eye ball in 50% ethanol for 2 days before sectioning
z Gross description of the eye should be recorded, appropriate measurements
of eye, tumor or pathologic processes also need to be recorded
z For decalcified bone techniques like frozen, paraffin, or celloidin sections,
transmission electron microscopy are used
z For mineralized bone frozen, plastic, scanning and transmission electron
microscopy techniques are used
z Inorganic calcium must be removed from the matrix by decalcification
either by acids or chelating agents
z Acid decalcifiers are strong inorganic acids like nitric acid and hydrochloric
acids and weak organic acids like fromic, acetic, picric acids
z Chelating agent used for decalcification is ethylene diaminetetraacetic acid
z Several factors like concentration and volume of active reagent, temperature
at which reaction takes place influence the rate of decalcification
z Acids from the tissues be removed from tissues or neutralized chemically
after decalcification is complete by either saturated lithium carbonate
solution or 5-10% aqueous sodium bicarbonate solution

TERMINAL QUESTIONS
1. Describe decalcification.
2. Enumerate the different methods of decalcification.
3. What are the advantages of EDTA decalcification?
4. What are the factors influencing the rate of decalcification?
5. Describe the special steps required before processing eyeball.

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Special Processing MODULE
Histology and Cytology

ANSWERS TO INTEXT QUESTIONS

17.1
1. 50% ethanol, 2 days
2. Decalcification
Notes
3. Nitric & Hydrochloric acid
4. Fromic, acetic & Picric acid
5. Ethylene-diaminetetraacetic acid (EDTA)

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 MODULE Fixation of Tissues

Histology and Cytology

5
Notes
FIXATION OF TISSUES

5.1 INTRODUCTION
It is a process by which the cells or tissues are fixed in chemical and partly
physical state so that they can withstand subsequent treatment with various
reagents, with minimal distortion of morphology and no decomposition.

OBJECTIVES
After reading this lesson, you will be able to:
z state the aims of fixation
z explain the principle of fixation
z describe the properties and factors affecting fixation
z explain types of fixation.

5.2 AIMS OF FIXATION

(a) To preserve the tissues as close to their living state as possible
(b) To prevent autolysis and bacterial attack
(c) To prevent tissues from changing their shape and size during processing
(d) To harden the tissues
(e) To allow clear staining of sections subsequently
(f) To improve the optical differentiation of cells & tissues

5.3 PRINCIPLE OF FIXATION

Fixation results in denaturation and coagulation of protein in the tissues. The
fixatives have a property of forming cross links between proteins, thereby
forming a gel, keeping everything in their in vivo relation to each other.

20 HISTOLOGY AND CYTOLOGY

Fixation of Tissues MODULE
Histology and Cytology
5.4 PROPERTIES OF FIXATIVES AND FACTORS
AFFECTING FIXATION
1. Coagulation and precipitation of proteins in tissues.
2. Penetration rate differs with different fixatives depending on the molecular
weight of the fixative
3. pH of fixatives – Satisfactory fixation occurs between pH 6 and 8. Outside
Notes
this range, alteration in structure of cell may take place.
4. Temperature – Room temperature is alright for fixation. At high temperature
there may be distortion of tissues.
5. Volume changes – Cell volume changes because of the membrane
permeability and inhibition of respiration.
6. An ideal fixative should be cheap, nontoxic and non-inflammable. The
tissues may be kept in the fixative for a long time.

5.5 TYPE OF FIXATION

z Immersion fixation
z Perfusion fixation
z Vapour fixation
z Coating/Spray fixation
z Freeze drying
z Microwave fixation/Stabilization
The most commonly used technique is simple immersion of tissues/smears in
an excess of fixative. For all practical purposes immersion fixatives are most
useful. These may be divided into routine and special.

5.6 SIMPLE FIXATIVES

1. Formaldehyde: Commercially available solution contains 35%-40% gas by
weight, called as formalin. Formaldehyde is commonly used as 4% solution,
giving 10% formalin for tissue fixation. Formalin is most commonly used
fixative. It is cheap, penetrates rapidly and does not over- harden the tissues.
The primary action of formalin is to form additive compounds with proteins
without precipitation. Formalin brings about fixation by converting the free
amine groups to methylene derivatives.
If formalin is kept standing for a long time, a large amount of formic acid
is formed due to oxidation of formaldehyde and this tends to form artefact
which is seen as brown pigment in the tissues. To avoid this buffered
formalin is used.

HISTOLOGY AND CYTOLOGY 21

 MODULE Fixation of Tissues

Histology and Cytology 2. Absolute alcohol – it may be used as a fixative as it coagulates protein.
Due to its dehydrating property it removes water too fast from the tissues
and produces shrinkage of cells and distortion of morphology. It penetrates
slowly and over-hardens the tissues.
3. Acetone – Sometimes it is used for the study of enzymes especially
phosphatases and lipases. Disadvantages are the same as of alcohol.
4. Mercuric chloride – It is a protein precipitant. However it causes great
Notes
shrinkage of tissues hence seldom used alone. It gives brown colour to the
tissues which needs to be removed by treatment with Iodine during
dehydration.
5. Potassium dichromate – It has a binding effect on protein similar to that
of formalin. Following fixation with Potassium dichromate tissue must be
well washed in running water before dehydration.
6. Osmic acid – It is used for fixation of fatty tissues and nerves.
7. Chromic acid – It precipitates all proteins and preserves carbohydrates.
Tissues fixed in chromic acid also require thorough washing with water
before dehydration.
8. Osmium tetraoxide – It gives excellent preservation of cellular details,
hence used for electron-microscopy.
9. Picric acid – It precipitates proteins and combines with them to form
picrates. Owing to its explosive nature when dry; it must be kept under a
layer of water. Tissue fixed in picric acid also require thorough washing with
water to remove colour. Tissue can not be kept in picric acid more than 24
hrs.

5.7 COMPOUND FIXATIVES

1. Formal saline - It is most widely used fixative. Tissue can be left in this
for long period without excessive hardening or damage. Tissues fixed for
a long time occasionally contain a pigment (formalin pigment). This may
be removed in sections before staining by treatment with picric alcohol or
10% alcoholic solution of sodium hydroxide. The formation of this pigment
can be prevented by neutralizing or buffering the formal saline.
Fixation time – 24 hours at room temprature
2. Formal calcium – Useful for demonstration of phospholipids.
Fixation time-24 hours at room temperature
3. Zenker’s fluid – It contains mercuric chloride, potassium-di-chromate,
sodium sulphate and glacial acetic acid.
Advantages – even penetration, rapid fixation

22 HISTOLOGY AND CYTOLOGY

Fixation of Tissues MODULE
Disadvantages – After fixation the tissue must be washed in running water Histology and Cytology
to remove excess dichromate. Mercury pigment must be removed with
Lugol’s iodine.
4. Zenker’s formal (Helly’s fluid) – In stock Zenker’s fluid, formalin is added
instead of acetic acid.
Advantages – excellent microanatomical fixative especially for bone
marrow, spleen & kidney. Notes
5. Bouins fluid – It contains picric acid, glacial acetic acid and 40%
formaldehyde.
Advantages – (a) Rapid and even penetration without any shrinkage. (b)
Brilliant staining by trichrome method. It is routinely used for preservation
of testicular biopsies.

Points to Remember
1. 10% buffered formalin is the commonest fixative.
2. Tissues may be kept in 10% buffered formalin for long duration.
3. Volume of the fixative should be atleast ten times of the volume of the
specimen. The specimen should be completely submerged.
4. Special fixatives are used for preserving particular tissues.
5. Formalin vapours cause throat/ eye irritation hence mask/ eye glasses and
gloves should be used.
6. Tissues should be well fixed before dehydration.
7. Penetration of fixatives takes some time. It is necessary that the bigger
specimen should be given cuts so that the central part does not remain
unfixed.
8. Mercury pigment must be removed with Lugol’s iodine.
9. Biopsies cannot be kept for more than 24 hours in bouin’s fluid without
changing the alcohol.
10. Glutaraldehyde and osmion tetraoxide are used as fixatives for electron
microscopy.

Most Commonly used Fixatives in the Laboratory are

10% Formalin
Formaldehyde (40%) - 10 ml
Distilled water - 90 ml

HISTOLOGY AND CYTOLOGY 23

 MODULE Fixation of Tissues

Histology and Cytology Formal Saline

Formaldehyde (40%) - 100 ml
Sodium Chloride - 9 gm
Distilled Water - 900 ml

10% Buffered Formalin

Notes Formaldehyde (40%) - 10 ml
Sodium dihydrogen phosphate - 0.4 gm
Disodium hydrogen phosphate (anhydrous) - 0.65 gm
Distilled water - 90 ml
The advantage of this fixative is that it prevents the formation of formalin
pigment

Bouin’s solution
Saturated picric acid (1.2 gm/ 100 ml) - 750 ml
Formaldehyde (40%) - 250 ml
Glacial acetic acid - 50 ml

Alcoholic formaldehyde
40% formaldehyde - 100 ml
95% alcohol - 900 ml
0.5 g calcium acetate may be added to this mixture to ensure neutrality

Alcohol containing fixatives

Carnoy’s fixatives -
Absolute ethanol - 60 ml
Chloroform - 30 ml
Glacial acetic acid - 10 ml

Mercury salt containing fixatives

Zenker’s fluid
Distilled water - 950 ml
Potassium dichromate - 25 gm
Mercuric Chloride - 50 gm
Glacial acetic acid - 50 gm

24 HISTOLOGY AND CYTOLOGY

Fixation of Tissues MODULE
B5 fixative Histology and Cytology

Stock reagent A
Mercuric chloride - 60 g
Sodium acetate - 12.5 g
Distilled water - 1000 ml
Stock Reagent B Notes
10% buffered neutral formalin
Working Solution
Stock reagent A - 90 ml
Stock reagent B - 10 ml
Fixation time - 5-8 hrs
Adequate time should be given for fixation. Formalin fixation should ideally be
given for at least 8 hours before processing. (Not the whole specimen but the
cut sections).

INTEXT QUESTIONS 5.1

1. Fixation results in .................... & .................... of protein in the tissues.
2. Most commonly used fixation technique is ....................
3. .................... is used as fixation for fatty tissues and nerves
4. Most widely used fixative is ....................
5. Volume of fixatives shuld be atleast .................... of the volume of the
specimen
6. Mercury pigment should be removed with ....................
7. .................... prevents the formation of formalin pigment
8. Which is the commonly used fixative for tissues
(a) Buffered formalin (b) Saline
(c) Glutaraldehyde (d) Bouin’s fluid
9. Which of the following is the best fixative for testicular biopsies?
(a) Buffered formalin (b) Zenker’s solution
(c) Saline (d) Bouin’s fluid

HISTOLOGY AND CYTOLOGY 25

 MODULE Fixation of Tissues

Histology and Cytology 10. What is used to remove colour from tissues fixed in Zenker’s solution?
(a) Alcohol (b) Lugol’s iodine
(c) Tap water (d) Acetone
11. Which of the following is used for fixation of tissues for electron
microscopy?
(a) Glutaraldehyde (b) Saline
Notes
(c) Osmic acid (d) Picric acid
12. What should be the optimum pH of fixative to preserve good morphology?
(a) 5 (b) 6
(c) 7 (d) 8

WHAT HAVE YOU LEARNT

z Fixation of tissues is a process by which the cells of tissue are fixed in
chemical and partly physical state so that they can withstand subsequent
treatment with various reagants
z Fixation results in denaturation and coagulation of protein in the tissues
z Penetration rate differs with molecular weight of the fixative
z Saturation fixation occurs between pH of 6 & 8 and optimally at 7
z An ideal fixative should be cheap, nontoxic and non inflammable
z Immersion, perfusion, vapour, coating/spray, freeze drying, micro waved
fixation are the different types of fixatives used
z The most commonly used technique is simple immersion of tissues/smears
in an excess of fixation
z Buffered formalin is the most commonly used fixative and prevents brown
pigment formation on tissues
z Following fixation with potassium dichromate tissue must be well washed
in running water
z Osmic acid is used for fixation of fatty tissues and nerves
z Osmium tetraoxide and glutaraldehyde are used for electron microscopy
z Formal saline is the most widely used fixative
z Formal Calcium is useful for demonstration of phospholipids
z Bouins fluid is routinely used for preservation of testicular biopsies

26 HISTOLOGY AND CYTOLOGY

Fixation of Tissues MODULE
z Mercury pigment must be removed with lugol’s iodine Histology and Cytology

z Formalin fixation should ideally be given for atleast 8 hours before

processing. Whole specimens should not be fixed without giving cuts.

TERMINAL QUESTIONS
Notes
1. What is a fixative?
2. What is the commonest fixative?
3. Write the properties of an ideal fixative.
4. What precautions should be observed when using formalin as fixative?
5. Write names of two special fixatives and their use.

ANSWERS TO INTEXT QUESTIONS

5.1
1. Denaturation and Coagulation
2. Simple immersion
3. Osmic acid
4. Formal Saline
5. Ten times
6. Lugol’s Iodine
7. Buffered Formalin
8. (a) Buffered formalin
9. (d) Bouin’s fluid
10. (b) Lugol’s iodine
11. (a) Glutaraldehyde
12. (c) 7

HISTOLOGY AND CYTOLOGY 27

 MODULE Decalcification

Histology and Cytology

6
Notes
DECALCIFICATION

6.1 INTRODUCTION
The presence of calcium salts in tissues makes them hard. This causes damage
to the knife, difficulty in cutting tissue. Calcium is normally present in bones
and teeth. Calcium may also be present in normal tissues in pathological
conditions like necrotic tissue in tuberculosis.

OBJECTIVES
After reading this lesson, you will be able to:
z describe decalcification
z explain different methods of decalcification
z describe the chemical and physical tests to estimate the remaining calcium.

6.2 DECALCIFICATION
Aim – To remove calcium salts from the tissues and make them amenable for
sectioning.
Preparation of tissues – The calcified hard tissues should be first cut into small
pieces (2 to 6mm) with a thin blade, hacksaw or sharp knife in order to minimize
the tearing of the surrounding tissues. This process is followed by fixation in
buffered formalin or any other desired fixative. After fixation tissues must be
thoroughly washed and excess fixative should be removed before the specimen
is subjected to decalcification.

6.3 DIFFERENT METHODS OF DECALCIFICATION

1. Acid decalcification
2. Ion exchange resin
28 HISTOLOGY AND CYTOLOGY
Decalcification MODULE
3. Electrical ionization Histology and Cytology

4. Chelating methods
5. Surface decalcification
Decalcification process should satisfy the following conditions-
z Complete removal of calcium salts
z Minimal distortion of cell morphology
Notes
z No interference during staining
Decalcification is a straightforward process but to be successful it requires:
z A careful preliminary assessment of the specimen

z Thorough fixation

z Preparation of slices of reasonable thickness for fixation and processing

z The choice of a suitable decalcifier with adequate volume, changed

regularly
z A careful determination of the endpoint
z Thorough processing using a suitable schedule

Methods of Decalcification
The tissue is cut into small pieces of 3 to 5 mm size. This helps in faster
decalcification. The tissue is then suspended in decalcifying medium with waxed
thread. The covering of wax on thread prevents from the action of acid on thread.
The volume of the decalcifying solution should be 50 to 100 times of the volume
of tissue. The decalcification should be checked at the regular interval.
Acid Decalcification – This is the most commonly used method. Various acid
solutions may be used alone or in combination with a neutralizer. The neutralizer
helps in preventing the swelling of the cells.
Following are the usually used decalcifying solutions -
1. Aqueous Nitric Acid-
Nitric acid - 5 ml
Distilled water - 100 ml
If tissue is left for long time in the solution, the tissue may be damaged.
Yellow colour of nitric acid should be removed with urea. But this solution
gives good nuclear staining and also rapid action.
2. Nitric Acid Formaldehyde
Nitric acid - 10 ml
Formaline - 5-10 ml

HISTOLOGY AND CYTOLOGY 29

 MODULE Decalcification

Histology and Cytology Distilled water upto 100 ml

Advantages
z Rapid action

z Good nuclear staining

z Washing with water is not required

z Formalin protects the tissues from maceration

Notes 3. Formic Acid Solution
Formic acid - 5 ml
Distilled water - 90 ml
Formalin - 5 ml
In this solution the decalcification is slow. If concentration of formic acid
is increased the process is fast but tissue damage is more.
4. Trichloroacitic Acid - This is used for small biopsies. The process of
decalcification is slow hence cannot be used for dense bone or big bony
pieces.
Formal saline (10%) - 95 ml
Tricloroacitic acid - 5 gm
Ion Exchange method – In these ammonium salts of sulfonated polystyrene
resin is used. The salt is layered on the bottom of the container and formic acid
containing fluid is filled. The decalcifying fluid should not contain mineral acid.
X-rays can only determine complete decalcification. The advantages of this
method are -
z Faster decalcification
z Well preserved tissue structures
z Longer use of resin
Electrolytic Method – Formic acid or HCl are used as electrolytic medium. The
calcium ions move towards the cathode. Rapid decalcification is achieved but
heat produced may damage the cytological details.
Chelating Agents – Organic chelating agents absorb metallic ions. EDTA can
bind calcium forming a non-ionized soluble complex. It works best for
cancerous bone. This is best method for decalcification of bone marrow biopsies
as it preserves cytological details best. The glycogen of marrow is preserved.
EDTA Solution
EDTA - 5.5 gm
Formaline - 100 ml
Distilled water - 900 ml

30 HISTOLOGY AND CYTOLOGY

Decalcification MODULE
Surface Decalcification – The surface layer of paraffin blocks are inverted in Histology and Cytology
5% HCl for one hour. About top 30 micron is decalcified. It should be washed
thoroughly before cutting.

Factors affecting rate of Decalcification

1. Concentration of decalcifying solution-Increased concentration of the

decalcifying agent fastens the reaction.
Notes
2. Temperature-The rate of decalcification increases with rise of temperature.
3. Density of bone-Harder bone takes longer time to decalcify.
4. Thickness of the tissue-Small tissue pieces decalcify earlier.
5. Agitation-Agitation increases the rate of decalcification.

6.4 METHODS OF DETERMINING OPTIMUM

DECALCIFICATION OR ENDPOINT
z Specimens should NOT be crowded together and should NOT contact the
bottom of container in order to provide complete decalcification.
z Over decalcification can also permanently damage specimen. The following
procedure help determine the correct end-point of decalcification.

End-Point of Decalcification:
z X-ray (the most accurate way)
z Chemical testing (accurate)
z Physical testing (less accurate and potentially damage of specimen)

Chemical Test:
The following solutions are needed to chemically test for residual calcium.
5% Ammonium Hydroxide Stock:
Ammonium hydroxide, 28% 5 ml
Distilled water 95 ml
Mix well
5% Ammonium Oxalate Stock:
Ammonium oxalate 5 ml
Distilled water 95 ml
Mix well

HISTOLOGY AND CYTOLOGY 31

 MODULE Decalcification

Histology and Cytology Ammonium Hydroxide/Ammonium Oxalate Working Solution:

Use equal parts of the 5% ammonium hydroxide solution and the 5% ammonium
oxalate solution.

Procedure
1. Insert a pipette into the decalcifying solution containing the specimen.
Notes
2. Withdraw approximately 5 ml of the hydrochloric acid/formic acid
decalcification solution from under the specimen and place it in a test tube.
3. Add approximately 10 ml of the ammonium hydroxide/ammonium oxalate
working solution, mix well and let stand overnight.
4. Decalcification is complete when no precipitate is observed on two
consecutive days of testing. Repeat this test every two or three days.

Physical Tests
The physical tests include bending the specimen or inserting a pin, razor, or
scalpel directly into the tissue. The disadvantage of inserting a pin, razor, or
scalpel is the introduction of tears and pinhole artifacts. Slightly bending the
specimen is safer and less disruptive but will not conclusively determine if all
calcium salts have been removed. After checking for rigidity, wash thoroughly
prior to processing.
Note: If paraffin embedded bones are not decalcified fully, one can soak the
paraffin blocks in the same decalcification solution for a few minutes before
cutting. This is usually helpful.

Points to remember
z After completion of decalcification, the specimen should be washed in
water
z Over decalcification is more noticeable in staining of nuclei.
z Acid solutions soften bone by removing calcium salts.
z EDTA is used as chelating agent for decalcification.
z To offset the hydrolysis of nucleic acids caused by decalcification, bone
marrow is often fixed in Zenker’s solution.
z During decalcification, carbon dioxide gas is released.
z Factors affecting decalcification are
o Size of specimen,
o Concentration of decalcifying solution,

32 HISTOLOGY AND CYTOLOGY

Decalcification MODULE
o Time in decalcifying solution Histology and Cytology

o Amount of decalcifying solution

z For proper decalcification, bone should be cut into 4-5mm thick pieces
z Chelating agents act by binding calcium ions

INTEXT QUESTIONS 6.1 Notes

1. Most commonly used method of decalcification is ......................
2. In Ion exchange method ...................... resin is used
3. ...................... or ...................... are used as electrolyte medium
4. ...................... is used as chelating agents
5. After decalcification, the specimen should be washed in ......................

WHAT HAVE YOU LEARNT

z Presence of calcium salts in tissues makes them hard and which causes
damages to knife and difficulty in cutting tissues
z Aim of decalcification is to remove calcium salts from the tissues and makes
them amenable for sectioning
z The calcified hard tissue should be first cut into small pieces and fixed in
buffered formalin
z Acid decalcification, Ion exchange resin, Electrical ionization, Chelating
methods and Surface decalcification are different methods of decalcification
z Decalcification must completely remove calcium salts, minimally distort
cell morphology and does not interfere during staining
z Acid decalcification is the most commonly used method. Various acids are
used in combination of neutralizer. The neutralizer helps in preventing the
swelling of the cells
z Ammonium salts of sulfonated polystyrene resin is used
z Formic acid or HCl are used as electrolytic medium
z Organic chelating agents absorb metallic ions and EDTA is used as chelating
agent
z Factors like concentration of decalcifying solution, Temperature, Density
of bone, thickness of tissue and agitation affects the rate of decalcification

HISTOLOGY AND CYTOLOGY 33

 MODULE Decalcification

Histology and Cytology

TERMINAL QUESTIONS
1. What is embedding?
2. What is the most common method used for decalcification of bony tissue?
3. Which decalcifying agent is best for bone marrow biopsy?
Notes 4. Name the factors affecting rate of decalcification.
5. What are the disadvantages if bony tissue is not decalcified before
sectioning?

ANSWERS TO INTEXT QUESTIONS

6.1
1. Acid decalcification
2. Ammonium salts of sulphonated polystyrene resin
3. Formic acid or HCL
4. EDTA
5. Water

34 HISTOLOGY AND CYTOLOGY

 MODULE Cytology : Staining Methods

Histology and Cytology

25
Notes
CYTOLOGY : STAINING
METHODS

25.1 INTRODUCTION
Consistency and reliability are most important in cytological interpretation.
Cytologists rely heavily on the quality and appearance of the stain. The
Papanicolaou stain is recommended for the staining of alcohol fixed cytology
slides. Romanowsky stains may also be used for wet fixed slides, but are
primarily applied to air-dried smears.
Special stains are used as per requirements: Modified Ziehl Neelson (for acid
fast bacilli), Gram staining (Bacteria), Mucicarmine (mucins), PAS (for
glycogen, fungal wall, lipofuscin, etc), Oil red O (lipids), Perl’s Prussian blue
(iron), modified Fouchet’s test (bilirubin), etc. Recently, immunocytochemistry
is also being increasingly used in cytology specimens. These special stains and
immunocytochemistry will be discussed along with respective sections in
histopathology as the principles and methods remain the same.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the principle of cytology stains
z explain the methods of staining cytology specimens.

25.2 STAINING IN CYTOLOGY

The universal stain for cytological preparations is the Papanicolaou stain. Harris’
hematoxylin is the optimum nuclear stain and the combination of OG6 and EA50
give the subtle range of green, blue and pink hues to the cell cytoplasm.

148 HISTOLOGY AND CYTOLOGY

Cytology : Staining Methods MODULE
Papanicolaou stain Histology and Cytology

Papanicolaou formula
1. Harris’ hematoxylin
Hematoxylin 5g
Ethanol 50ml
Potassium alum 100g Notes
Distilled water (50°C) 1000ml
Mercuric oxide 2-5g
Glacial acetic acid 40ml
2. Orange G 6
Orange G (10% aqueous) 50ml
Alcohol 950ml
Phosphotungstic acid 0-15g
3. EA 50
0.04 M light green SF 10ml
0.3M eosin Y 20ml
Phosphotungstic acid 2g
Alcohol 750ml
Methanol 250ml
Glacial acetic acid 20ml
Filter all stains before use.
Original Papanicolaou staining method:
1. 96% ethyl alcohol 15 seconds
2. 70% ethyl alcohol 15 seconds
3. 50% ethyl alcohol 15 seconds
4. Distilled water 15 seconds
5. Harris hematoxylin 6 minutes
6. Distilled water 10 dips
7. Hydrochloric acid 0.5% solution, 1-2 quick dips
8. Distilled water 15 seconds
9. Few dips in 0.1% ammoniated water. The smear turns to blue.

HISTOLOGY AND CYTOLOGY 149

 MODULE Cytology : Staining Methods

Histology and Cytology 10. 50% ethyl alcohol 15 seconds

11. 70% ethyl alcohol 15 seconds
12. 96% ethyl alcohol 15 seconds
13. OG-6 (orange) 2 minutes
14. 96% ethyl alcohol 10 dips
Notes 15. 96% ethyl alcohol 10 dips
16. EA 50 eosin yellowish 3 minutes
17. 96% ethyl alcohol (10 dips)
18. 100% ethyl alcohol (10 dips)
19. Xylene (10 dips)
20. Mount: in DPX using coverslip

Results:
The nuclei should appear blue/black
The cytoplasm (non-keratinising squamous cells) – blue/green
Keratinising cells- pink/orange
Precautions:
1. Use stains only after filtering them
2. Change stains frequently
3. Check staining under microscope for good quality control

25.3 MAY-GRÜNWALD GIEMSA STAIN

This is one of the common Romanwsky stains used in cytology. It is useful for
studying cell morphology in air-dried smears. It is superior to Papanicolaou to
study the cytoplasm, granules, vacuoles, basement membrane material etc. For
nuclear staining Papanicolaou is superior.
Contents of the staining reagents:
May-Grünwald solution 0.2%
Methanol 99 %
May-Grünwald´s eosin-methylene blue 0.2 %
Contains: Eosin G, Methylene blue

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Cytology : Staining Methods MODULE
Giemsa solution Histology and Cytology

Methanol 73 %
Glycerol 26 %
Giemsa´s Azur-Eosin-Methylene blue 0.6 %
Contains: Azur I, Eosin G, Methylene blue
Notes
Phosphate buffer
Potassium dihydrogen phosphate/ disodium hydrogen phosphate x 2H2O
67.0 mmol/l

Storage
Giemsa solution, May-Grünwald solution: protected from light at 2-25°C.
Unopened reagents may be used until the expiry date on the label.
Phosphate buffer: at 2-8°C. Unopened reagents may be used until the expiry date
on the label.

Preparation of working solutions

1. Buffered water: Dilute phosphate buffer with deionised or distilled water
1:20, e.g. 30 ml phosphate buffer + 570 ml deionised or distilled water.
2. Giemsa working solution : Mix 84 ml of Giemsa solution into 516 ml of
buffered water.
3. May-Grünwald working solution: Mix 360 ml of May-Grünwald solution
into 240 ml of buffered water.

Staining method
1. Fix the air-dried smear specimen in methanol for 10 -20 minutes
2. Stain with May-Grünwald working solution for 5 minutes
3. Stain with Giemsa working solution for 12 minutes
4. Wash with clean buffered water for 2, 5 and 2 minutes
5. Dry the slides in upright position at room temperature
6. Mount the slides with a coverslip using DPX
Any modifications to the staining procedure/working solutions may affect the
staining result, and are subject to precise method validation

HISTOLOGY AND CYTOLOGY 151

 MODULE Cytology : Staining Methods

Histology and Cytology Sources of errors

Irregular distribution of the blood smear on a glass slide may result in an
erroneous cell counts. Alcohols used for wiping the skin may cause hemolysis
and artifacts. Do not let the specimens dry at any stage of the staining procedure.
Wash properly to avoid dye artifacts. Buffered water is strongly recommended
for washing. Staining result is dependent on pH. Alkaline pH increases blue and
acidic pH pink or reddish tinge in the stained specimen.
Notes

Ziehl-Neelsen stain
Reagents
(1) Carbol Soft Fuchsin
Basic Fuchsin 1 gm
Absolute alcohol 10 ml
Add the basic fuchsin to the alcohol in a 100 ml flask and mix, on a
magnetic stirrer for 30 minutes. Add 100ml of 5% aqueous phenol. Mix
well. Filter and store in a brown glass bottle.
(2) Acidified Methylene Blue
0.25% methylene blue in 1% acetic alcohol
(3) 0.5% Acid Alcohol
Distiller water 700 ml
Absolute alcohol 300 ml
Hydrochloric acid 5 ml
(6) 5% Sulphuric Acid
Distilled water 475 ml
Sulphuric acid 25 ml

Staining Method
Place fixed slides on the staining rack in serial order, smeared side up. Slides
should be separated by a 1 cm gap, and should never touch one another. Cover
slides individually with filtered Ziehl’s carbol fuchsin working solution. Heat
slides from underneath with the flame of a Bunsen burner, an alcohol lamp or
an alcohol soaked cotton swab until vapour starts to rise. Staining solution
should never be allowed to boil. Do not allow the stain to dry. Keep slides
covered with hot, steaming carbolfuchsin for 5 minutes by re-flaming as needed.
Rinse slides gently with water to remove excess carbolfuchsin. Drain off excess
rinsing water from slides. Sputum smears appear red in colour.

152 HISTOLOGY AND CYTOLOGY

Cytology : Staining Methods MODULE
Decolourising: Cover slides with 25% sulfuric acid or acid-alcohol solution and Histology and Cytology
allow to stand for 3 minutes, after which the red colour should have almost
completely disappeared. If needed, repeat sequence until the red colour
disappears, but do not overdecolourise. Gently wash away the sulfuric acid or
acid alcohol and the excess stain with water. Drain off excess rinsing water from
slides.
Counterstaining: Cover slides individually with 0.3% methylene blue Notes
counterstaining solution and allow to stand for 1 minute. Rinse slides individually
with water. Drain water off the slides, which are then allowed to air dry.
A properly stained smear should show a light blue colour due to methylene blue.
Results: Tubercle bacilli, hair shafts, Actinomyces, some fungal elements- red.
Background: pale blue.

INTEXT QUESTIONS 25.1

1. ................... stain is recommended for stains of alcohol fixed cytology
2. ................... stain is used for wet fixed slides
3. ................... stain is used for identification of Glycogen, Fungal Wall
4. ................... stain is used for identification of lipids
5. ................... test is used for identification of Bilirubin
6. The universal stain for cytological preparations is the ...................

WHAT HAVE YOU LEARNT

z Consistency and reliability are most important in cytological interpretation.
Cytologists rely heavily on the quality and appearance of the stain.
z Special stains such as Modified Ziehl Neelson for acid fast bacilli, Gram
staining for Bacteria, Mucicarmine for mucins, PAS for glycogen, fungal
wall, lipofuscin, Oil red O for lipids, Perl’s Prussian blue for iron, modified
Fouchet’s test for bilirubin
z The universal stain for cytological preparations is the Papanicolaou stain.
Harris’ hematoxylin is the optimum nuclear stain
z May-Grünwald Giemsa Stain is one of the common Romanwsky stains used
in cytology. It is useful for studying cell morphology in air-dried smears.

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Histology and Cytology z Irregular distribution of the blood smear on a glass slide may result in an
erroneous cell counts. Alcohols used for wiping the skin may cause
hemolysis and artifacts

TERMINAL QUESTIONS
Notes
1. What are the various stains used commonly in cytology.
2. Write the basic principle of Papanicolaou staining.
3. What cell components are better seen in MGG staining?
4. Name the sources of error in Papanicolaou & MGG staining.
5. Enumerate the substances that get stained red with Ziehl Neelsen staining.

ANSWERS TO INTEXT QUESTIONS

25.1
1. Papanicolaou stain
2. Romanowsky
3. PAS
4. Oil red O
5. Modified Fouchet’s
6. Papanicolaou stain

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Histology and Cytology

14
Notes
STAINING TECHNIQUES FOR
DEMONSTRATION AND
IDENTIFICATION OF
MICROORGANISMS

14.1 INTRODUCTION
Traditional methods for the demonstration of microorganisms in tissue sections
can only be based upon staining characteristics and simple morphology because
the organisms are fixed and dead. When it is suspected that a disease process
may be caused by, or complicated by an infective agent, a sample of fresh tissue
is normally provided for microbiological evaluation. The most effective means
of isolating and identifying individual species of most organisms is to study their
growth patterns and morphology in vitro. The study of these criteria has formed
the basis for the identification and classification of microorganisms

OBJECTIVES
After reading this lesson, you will be able to:
z describe Ziehl-Neelsen stain
z demonstrate Fite acid fast stain
z explain periodic acid Schiff, Mucicarmine stain.

IDENTIFICATION OF BACTERIA

Most of the bacteria are demostrated by

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Histology and Cytology

14.2 GRAM STAIN
Some of the bacteria like mycobacterium do not get stained with Gram stain due
to their lipid capsule.Ziehl-Neelsen stain is applied to identify mycobacteria
which are stained pink to red in colour.

14.2.1 Gram Staining

Notes This reaction may depend on the difference in permeability of cytoplasmic
membrane.During staining a dye iodine complex is formed whithin the
cell,which is insoluble in water.The complex diffuses freely from gram negative
organisms but diffuses less in Gram positive bacteria due to poor membrane
permeability.

14.2.2 Preparation of reagents

Crystal violet solution

Crystal violet 1.0gm
Absolute alcohol 20ml
Ammonium oxalate(1%) 80ml

Basic fuchsin
Basic fuchsin 1.0gm
Distilled water 100ml

Gram’s iodine
Iodine crystal 1.0gm
Potassium iodide 2.0gm
Distilled water 300ml

14.2.3 Procedure
z Deparaffinize the section and bring it to water
z Put crystal violet for one minute
z Add Gram’s iodine for 30 seconds
z Differentiate by dipping the section once or twice in alcohol
z Wash with water and counterstain with safranin for 45 seconds
z Wash with water

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Histology and Cytology
z Air dry and mount in DPX.RESULT Gram positive bacteria stain blue
black.
z Gram negative bacteria stain red or pink.
z Some of the bacteria like mycobacterium do not get stained with Gram stain
due to their lipid capsule.Ziehl-Neelsen stain is applied to identify
mycobacteria which are stained pink to red in colour .
Notes
14.3 ZIEHL-NEELSEN STAIN (ACID FAST STAIN)
Aim: To demonstrate Mycobacterium Tuberculosis in paraffin sections.
Principle: When Mycobacterium Tuberculosis are stained with a strong reagent
like basic fuchsin in aqueous 5% phenol at high temperature the bacilii resist
decolourization by strong acids (20% sulphuric acid). Any decolourized non
AFB is counterstained with methylene blue or malachite green.
Control: Mycobacterium tuberculosis positive section

Reagents
1. Ziehl-Neelsen’s carbol fuchsin
Basic fuchsin 1gm
Absolute alcohol 10ml
5% phenol (Aqueous) 100ml
Dissolve basic fuchsin in alcohol, and then add 5% phenol.
2. Methylene blue solution
Methylene blue 1gm
Distilled water 100ml

Procedure
z De-wax the sections in xylene and bring to water.
z Flood sections with carbol fuchsin and heat to steaming by intermittent
flaming for 10 to 15 minutes or stain in coplin jar at 56°-60°C (oven or
water bath) for 30 minutes.
z Wash in water to remove excess of stain.
z Differentiate with 20% sulphuric acid or in 3% hydrochloric acid in 70%
alcohol until the tissue is very pale pink colour. Then washed in water (for
5 to 10 minutes).

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Histology and Cytology z Wash in water.

z Counterstain in 1% methylene blue for 10 to 15 seconds.
z Wash in water.
z Dehydrate, clear in xylene and mount in DPX.

Result
Notes
Acid-Fast Bacilii – red
Nuclei – blue
Back ground – pale blue

14.4 FITE ACID FAST STAIN - LEPROSY

Aim: To demonstrate mycobacterium leprae (leprosy), in formaline fixed
sections.
Principle: This technique combines peanut oil with xylene, minimizing the
exposure of the bacteria’s cell wall to organic solvent. Thus acid fastness of
bacteria is retained.
Control: Leprosy positive tissue.

Reagents
1. Xylene/Peanut Oil Solution:
Xylene 50.0 ml
Peanut Oil 50.0 ml
Mix well. Label with date, solution is stable for 1 year
Caution: The solution is inflammable, irritant
2. Ziehl-Neelsen Carbol-Fuchsin:
As described before
3. 1% Acid Alcohol
4. Methylene Blue:
Methylene blue 1.0 gm
Distilled water 100 ml

Procedure
z De-paraffinize the section for two minutes in xylene and peanut oil mixture

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z Drain, wipe excess of oil Histology and Cytology

z Place the slide in water until ready to stain

z Put Carbol - fuchsin, for 30 minutes, at room temperature
z Wash in tap water
z Dip acid alcohol until pale pink, dip until stain stops running
z Wash in tap water
Notes
z Counter-stain in methylene blue solution for 30 seconds
z Wash in tap water
z Blot and air dry
z Dip in xylene and mount with DPX and put coverslip

Results
Acid-fast bacilli – red
Background – blue
Note: Mineral oil may be substituted for peanut oil.

14.5 PERIODIC ACID – SCHIFF (PAS) STAIN

Periodic acid causes oxidation of 1:2 glycol groups in the tissues to di-aldehydes.
The di-aldehyde reacts with fuchsin – sulfurous acid solution(Schiff’s) to form
a magenta colored compound.
Aim: To demonstrate glycogen, epithelial mucin, fungi, ameba and basement
membrane.
Control: Liver and intestine

Reagents
Periodic acid 1%
Distilled water 100 m

Schiff’s reagent
Basic fuchsin 1 gm
Distilled water 200 ml
1N hydrochloric acid 20 ml
Sodium or Potassium metabitesulfite1gm
Activated charcoal 2gm

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Histology and Cytology z Dissolve basic fuchsin in boiling distilled water

z Shake for 5 minutes and cool to 50°C
z Filter and add 1N solution.
z Cool further and add sodium or potassium metabisulfite. Keep for 18 hours
in dark.
z Add activated charcoal, shake well, filter and store the solution at 40°C.
Notes
Procedure
z Bring the sections to water.
z Dip the slide in Periodic acid solution for 5-10 minutes.
z Wash in tap water and rinse in distilled water.
z Put Schiff’s reagent on the section for 20 minutes.
z Wash thoroughly in running water.
z Counerstain with Hematoxylin, dehydrate, clear and mount in DPX.

Result
z Glycogen (except non-sulfated acid mucopolysaccharide), basement
membrane, fungi, parasites and other positive substances – magenta
z Nucleus – blue or violet

Giemsa stain
Aim: It is used to demonstrate
z Bacteria, Hematologic element, Bone marrow elements, Blood parasites

Reagents
Giemsa stain
Stock solution:
Giemsa powder 1.0 gm
Methyl alcohol 66 ml
Glycerin 66 ml
Add glycerin to Giemsa powder and put in oven at 60oC for 30 minutes to 2 hours
(until the stain dissolves). Then add methyl alcohol.
Working solution:
Stock solution 1.25 ml
Methyl alcohol 1.50 ml
Distilled water 50 ml

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Procedure Histology and Cytology

z Deparaffinize and take the section to water.

z Place the slide in working Giemsa solution overnight.
z Wash with tap water.
z Differentiate with 0.5% aquous acitic acid.
z Dehydrate and mount. Notes

Result
Nuclei – blue
Malarial parasite – purple
Collagen and other elements – pink

Note:
1. Sections stained at room temperature for longer period show better results
than sections stained at higher temperature for shorter period.
2. Differentiation with acetic acid removes only blue dye hence gives better
red intensity.
3. Giemsa reagent improves with age.

14.6 MUCICARMINE STAIN

Aim: To demontrate mucin glycogen in tissues.

Principal: Aluminum is believed to form a chelation complex with carmine

changing the molecule to a positive charge allowing it to bind with the acid
substrates of low density such as mucus.

Reagents
1. Mucicarmine solution
Carmine alum lake 1.0 gm
Aluminum hydroxide 1.0 gm
50% alcohol 100 ml
z Mix well and add anhydrous Aluminum chloride 0.5 gm
z Boil gently for 2 to 3minutes, cool, filter and refrigerate (may be stored for
6 months)

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Histology and Cytology 2. Metanil yellow solution

Metanil yellow 0.25 gm
Distilled water 100 ml
Glacial acetic acid 0.25 ml
Mix well (may be stored for one year)
Notes 3. Harris hematoxylin

Procedure
z Deparaffize and bring the section to water.
z Mayer’s hematoxylin for 10 minutes.
z Wash in running tap water for 5 minutes.
z Mucicarmine solution for one hour at room temperature.
z Rinse quickly in distilled water.
z Metanil yellow for 30 seconds to 1minute.(optional)
z Three changes of absolute alcohol.
z Dehydrate, clear and mount in DPX.

Result
Mucin – deep rose
Nuclei – black
Other tissue elements – yellow (if metanil yellow is used)
– colorless (if metanil yellow is not used)
Capsule of cryptococci (fungus) – deep rose
Control small intestine

14.7 GROCOTT-GOMORI’S METHANAMINE SILVER

STAIN
Aim: To demonstrate fungi and bacteria particularly to stain carbohydrate. Cell
wall of fungi like Pnemocystis Jiroveci is outlined by black stain.

Reagents
z 0.5% aqueous periodic acid

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z Methanamine silver stock solution Histology and Cytology

3% methanamine 100ml
5% silver nitrate 5ml
z Add the silver nitrate solution to methanamine solution and mix it properly.
A white precipate will form and redissolve on shaking. Filter the stock
solution in brown bottle (stable for 6 months at 4°C).
Methanamine silver working solution- Notes
Stock solution 50ml
5% sodium borate 5ml
1. Mix well and filter.
2. Preheat for 10 to 20 minutes at 60°C prior to actual use.
3. 0.2% gold chloride
4. 3% sodium thiosulfate
5. Light green

Procedure
z Deparaffinze slides to distilled water.
z Oxidize in 0.5% periodic acid for 15 minutes at room temperature.
z Rinse three time in distilled water.
z Incubate the slides in methanamine silver working solution for 30 minutes
to one hour at 60°C.
z Rinse in hot distilled water and check microscopically.
z Rinse in distilled water at room temperature.
z Tone in gold chloride solution for one minute.
z Rinse in distilled water.
z Treat with sodium thiosulfate solution for 2 minutes.
z Wash in running tap water for 10 minutes.
z Counterstain in nuclear fast red or light green for 5 minutes.
z Dehydrate, clear in xyline and mount in DPX.

Result
Basement membrane black

Fungi cell wall black

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Histology and Cytology Background pink or green (depends on counterstain nuclear fast
red or light green)

Control kidney or skin

Notes INTEXT QUESTIONS 14.1

1. Mycobacterium Tuberculosis in paraffin section is demonstrated by
.....................
2. ..................... or ..................... is used as counter stain
3. Periodic acid Schiff stain is used to demonstrate ....................., .....................
& .....................
4. In periodic acid Schiff stain the nucleus appears ..................... & glycogen,
fungi, parasites appear .....................
5. Mucin in tissue is demonstrated by ..................... stain
6. ..................... stain is used to demonstrate fungi and bacteria
7. In Grocott-Gromori’s methanamine silver stain the fungal cell wall and
basement membrane appears ..................... & background appears
.....................
8. The control used in Grocott-Gromori’s Methanamine silver stain is
..................... or .....................

WHAT HAVE YOU LEARNT

z Ziel-Neelson stain is used to demonstrate mycobacterium tuberculosis in
paraffin sections
z Methylene blue or malachite green is used as counter stain
z Fite acid fast stain is used to demonstrate mycobacterium leprae in
fromaline fixed sections and this technique combines peanut with xylene
z Periodic acid schiff stain is used to demonstrate glycogen, epithelial mucin,
fungi and amaeba
z Liver and intestine is used as control in periodic acid Schiff stain
z Giema stain is used to demonstrate bacteria and blood parasites

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z In Giema stain nuclei appears blue, malarial parasite appears purple and Histology and Cytology
collagen and other elements appear pink
z Mucin in tissue is demonstrated by mucicarmine stain
z Grocott-Gomori’s Methanamine silver stain is used to demonstrate fungi
and bacteria particularly to stain carbohydrate

Notes

TERMINAL QUESTIONS
1. What are the stains which may be used to demonstrate fungi?
2. What is the principle of silver methanamine staining?
3. What is the difference in Acid Fast staining for Mycobacterium Tuberculosis
and Leprae?
4. What are the uses of Giemsa stain?
5. What control is used in PAS stain?

ANSWERS TO INTEXT QUESTIONS

14.1
1. Ziel-Neelson stain
2. Methylene blue or Malachite green
3. Glucogen, fungi & ameba basement membrane
4. Blue or violet, Magenta
5. Mucicarmine
6. Grocott-Gomori’s Methanamine Silver stain
7. Black, Pink or green
8. Kidney or skin

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Histology and Cytology

11
Notes
STAINING METHODS TO
DEMONSTRATE SPECIAL/
SPECIFIC TISSUES

11.1 INTRODUCTION
Biological tissue has little inherent contrast in either the light or electron
microscope. Staining is employed to give both contrast to the tissue as well as
highlighting particular features of interest. Where the underlying mechanistic
chemistry of staining is understood, the term histochemistry is used.

OBJECTIVES
After reading this lesson, you will be able to:
z describe various staining methods for demonstrating special tissues.
z demonstrate various staining methods.

11.2 TRICHROME STAIN

A combination of three different dyes is used to identify different cells and tissue
elements.
Aim: To identify the collagen and muscle fibers in a histological section.

Reagents
1. Bouin’s solution
z Saturated picric acid 75ml
z Formaldehyde (37-40%) 25ml
z Glacial acetic acid 5ml

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Histology and Cytology z Mix all the reagents well. This solution improves the trichrome stain
quality.
2. Weigert’s iron hematoxylin stock solution
Stock solution A
z Hematoxylin 1gm
z 95% alcohol 100ml
Notes
Stock solution B
z 29% Ferric chloride in water 4ml
z Distilled water 100ml
z Hydrochloric acid, concentrated 1.0ml
3. Weigert’s iron hematoxylin working solution - Mix equal parts of solution
A and B (This solution works for three months.)
4. Biebrich scarlet acid fuchsin solution
z 1% Biebric Scarlet-Acid Fuchsin solution (aqueous solution) 90ml
z 1% Acid Fuchsin (Aqueous) 10ml
z 1% Glacial acitic acid 1ml
5. Phosphomolybdic acid-Phosphotungstic Acid Solution
z 5% Phosphomolybdic Acid 25ml
z 5%phosphotungstic Acid 25ml
6. Aniline blue solution
z Aniline blue solution 2.5gm
z Glacial acitic acid 2ml
z Distilled water 100ml
Control: skin

Procedure
1. De-paraffinize and rehydrate through graded alcohol.
2. Wash in distilled water.
3. Fix the slides in Bouin’s solution for one hour at 560C.
4. Rinse in running tap water for 5 to 10 minutes to remove yellow color.
5. Stain in Weigert’s Iron Hematoxylin solution for 10 minutes.
6. Rinse in warm tap water for 10 minutes.
7. Wash in distilled water.

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8. Put Biebric Scarlet Acid Fuchsin solution for 10 to 15 minutes. Histology and Cytology

9. Wash in distilled water.

10. Differentiate in Phosphomolybdic-Phosphotungstic Acid solution for 10 to
15 minutes.
11. Put the sections in Aniline blue solution for 5-10 minutes.
12. Rinse in distilled water briefly.
Notes
13. Differentiate in acetic acid solution for 2-5 minutes.
14. Wash in distilled water.
15. Dehydrate quickly through 95% alcohol and absolute alcohol. (These steps
will wipe off Biebric Scarlet acid Fuchsin staining)
16. Clear in xyline and mount in DPX.

Result
z Glycogen, muscle fibre and keratin red
z Collagen and bone blue/green
z Nuclei brown/black
Note: This stain can be used on frozen sections also.

11.3 VERHEOFF STAIN FOR COLLAGEN

Aim: To identify collagen and elastic tissue in the same section.
Principle: In the presence of ferric salts (oxidizers) elastic fibers stain with
hematoxylin, along with the nuclei.
Control: skin

Reagents
1. Verhoeff’s solution: Freshly prepared solution gives best result.
Solution A
z Hematoxylin 5gm
z Absolute alcohol 100ml
z Dissolve hematoxylin with the aid of heat, cool and filter.
Solution B
z Ferric chloride 10gm
z Distilled water 100ml

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Histology and Cytology Solution C

z Iodine 2gm
z Potassium iodide 4gm
z Distilled water 100ml
z Add 8ml of solution B into 20ml of solution A and then add 8ml of
solution C.
Notes
2. 2% Ferric chloride solution
3. 1% aqueous solution of acid fuchsin
4. Saturated aqueous solution of picric acid
5. Van Gieson’s stain
z Acid Fuchsin 1% (aqueous) 5ml
z Saturated aqueous solution of picric acid 100ml
6. Sodium thiosulphate, 5% (aqueous solution)

Procedure
1. Deparaffinize and take the section to water.
2. Stain in Verhoeff solution until the section is black.
3. Wash in distilled water.
4. Differentiate in 2% Ferric chloride with agitation for few minutes. Check
differentiation by rinsing in distilled water. Under the microscope the elastic
fibers and nuclei should stain black and rest of the tissue should be light
grey.
5. Put in 5% sodium thiosulphate for 1 minute.
6. Wash in tap water for 5minutes.
7. Counter-stain with Van Gieson’s stain for 1-2 minutes.
8. Differentiate in 95% alcohol.
9. Dehydrate in absolute alcohol two times.
10. Clear in xylene and mount in DPX.

Result
z Elastic fibres black
z Nuclei black
z Collagen red
z Other tissues yellow
Note: It is a rapid method but fails to demonstrate fine fibers.

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Histology and Cytology
11.4 PRUSSIAN BLUE STAIN
Aim: To demonstrate the presence of iron in tissues.
Principle: The ferric iron in tissue combines with potassium ferro cyanide to
form ferric-ferro cyanide. This compound has bright blue color (prussian blue).
Prussian blue precipitate is insoluble, hence it can be combined with other
staining methods.
Notes
Control: Hemosiderin positive tissue

Reagents
1. 2%Hydrochloric acid
z concentrated hydrochloric acid 2ml
z Distilled water 98ml
2. 2% potassium ferrocyanide
z Potassium ferrocyanide 2mg
z Distilled water 100ml
3. 0.15% Basic fuchsin
z Basic fuchsin 0.15gm
z 50% ethyl alcohol 100ml

Procedure
1. Bring section to water.
2. Mix equal volume of 2% potassium ferrocyanide and 2% hydrochloric acid.
Pour the solution on the slide and keep it for 20 minutes.
3. Wash thoroughly with water.
4. Counter-stain with basic fuchsin or eosin for 30 seconds.
5. Wash with water, dehydrate, clear in xylene and mount in DPX.

Result
z Ferric iron blue
z Nuclei red
z Other tissues shades of pink
Note: All traces of ferrocyanide should be removed before it is counter-stained,
otherwise a dark red fine precipitate will form.

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Histology and Cytology

11.5 MASSON FONTANA SILVER STAINING
Aim: To demonstrate the presence of argentaffin granules.
Principle: Granules in argentaffin cells reduces ammoniacal silver solution to
metallic silver. This histo-chemical reaction is due the presence of 5 hydroxy
tryptamine(5HT).The 5HT must be converted to tetrahydri-carbolin derivative
by formalin fixation before reactions can be demonstrated.
Notes
Control: skin or any positive tissue

Reagents
1. Stock 10% silver nitrate solution
z Silver nitrate A R grade 10gm
z Distilled water 100ml
2. Fontana masson silver nitrate solution
z To 50 ml of 10% silver nitrate solution, add one or two drops of
ammonium hydroxide. The first drop itself will cause a brown precipitate.
Continue to add ammonia solution drop by drop just until the solution
is clear. From stock 10% silver nitrate solution, add a little more solution
drop by drop dissolving the initial precipitate and stop when a permanent
faint turbidity is attained. Let it stand overnight to settle. Before use,
decant silver solution, filter and dilute with an equal amount of distilled
water. Prepare the fresh solution each time.
3. Gold chloride solution
z Gold chloride 1gm
z Distilled water 500ml
z Keep the solution in refrigerator.
4. Sodiumthiosulfate 5gm
z Distilled water 100ml

Procedure
1. Bring sections to distilled water
2. Treat with Fontana silver nitrate solution for 1 hour at 56-58IN0C
ammoniacal silver solution in a closed jar 15 mins
3. Check microscopically and repeat step 2 if necessary

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4. Wash well in distilled water Histology and Cytology

5. Tone with gold chloride 2 minutes

6. Wash well with distilled water
7. Fix in 2% aq sodium thiosulphate 2 minutes
8. Wash well with distilled water
9. Counter-stain with neutral red stain 1 minutes Notes
10. Rinse in distilled water
11. Rapidly dehydrate well in absolute alcohol, clear and mount

Results
z Melanin black
z Argentaffin cell granules black
z Some lipofuscins black
z Chromaffin black
z Nuclei red

Note
z Formalin fixation is essential for argentaffin substances, but not critical for
melanin.
z A known positive control section must be used to ensure correct demonstration
has been achieved.
z Time of the ammoniacal silver impregnation depends upon the tissue
component to be demonstrated. At room temperature, melanin will require
12 hrs, argentaffin 24 hrs. At 60°C melanin blackens within 20 minutes,
argentaffin requires approximately 40 minutes. Excessive heat over long
periods may cause the silver solution to precipitate, give non-specific
background deposits, and cause precipitation of silver on connective tissue
fibres.
z Ammoniacal silver solutions can be explosive when allowed to dry.
Immediately after use neutralise the silver solution with saturated sodium
chloride and discard.

11.6 VON-KOSSA STAIN

Aim: To demonstrate calcium in paraffin sections.
Principle: Tissue sections are treated with silver nitrate solution, the calcium
is reduced by the strong light and replaced with silver deposits, visualized as
metallic silver.

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Histology and Cytology Reagents

5% silver nitrate solution
z Silver nitrate 25gm
z Distilled water 500ml
Mix well, pour into acid bottle. Store in refrigerator (stable for one year).
Notes Control: Positive control

Procedure
z Bring sections to water. One section works as negative control.
z Immerse one section in citrate buffer (pH4.5) for 20 minutes to remove
calcium if it is present.
z Wash both the slides in distilled water.
z Put 5% silver nitrate solution.
z Expose the slides to bright sun light for 10 to 20 minutes.
z Wash in distilled water several times.
z Treat with 5% sodium thiosulfate for 2 to 3 minutes.
z Wash well in water.
z Counter-stain with neutral red or Van Gieson stain.
z Dehydrate, clear in xylene and mount in DPX.

Result
z Calcium Dark green or black
z Back ground Depends on counter stain.
Note: Silver nitrate is tumorogenic and oxidizer. It is strong skin and eye irritant.

11.7 PHOSPHO-TUNGSTIC-ACID-HEMATOXYLIN STAIN

Aim: It is a mix of hematoxylin and phosphotungstic acid. Muscle cross
striations, fibrin and glial fibers can be demonstrated by this stain.
Principle: The phosphotungstic acid all of the available hematin to form a blue
lake pigment. This lake stains the muscle cross striations, fibrin and nuclei. The
rest of the phosphotungstic acid stains red brown, components like collagen.
Control: Skeletal muscle, cardiac muscle, fibrin, cerebral cortex for glial fibers.

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Reagents Histology and Cytology

z Hematoxylin 1gm
z Phosphotungstic acid 20gm
z Distilled water 1000ml
Dissolve the solid ingredients in separate portions of the water, the hematoxylin
with aid of gentle heat. When cool mix it. Allow the mixture to ripen or add
Notes
177gm of potassium permagnate for immediate use. Properly ripened stain is
rich purple in color and opaque.
0.25% potassium permagnate
z Potassium permagnate 0.25gm
z Distilled water 100ml
5% oxalic acid
z Oxalic acid 5gm
z Distilled water 100ml

Procedure
1. Dehydrate and bring section to water.
2. Oxidize in potassium permagnate for 5 to 10 minutes. Discard the solution.
3. Wash in water.
4. Bleach in oxalic acid for 5 minutes or until the sections are colorless.
5. Wash thoroughly. Rinse in distilled water.
6. Put PTAH stain for 12 to 24 hour.
7. Transfer the section into 95% alcohol, followed by absolute alcohol.
8. Dehydrate, clear in xyline and mount in DPX.

Result
z Striated muscle fibers blue
z Astrocytes blue
z Fibrin blue
z Nuclei blue
z Cytoplasm brown red
z Collagen brown pink

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Histology and Cytology

11.8 STAIN FOR RETICULIN FIBRES
Aim: To identify reticulin fibers in sections.
Principle: Reticulin fibers are treated with potassium permagnate to produce
sensitized sites for silver deposition. Silver is in a form readily able to precipitate
as metallic silver. Formalin, a reducing agent causes deposition of metallic silver
at pH 9.0.Excess silver is removed by sodium thiosulphate solution .Treatment
Notes with gold chloride produces permanent precipitate.
Control: Normal liver.

Reagents
Acidified potassium permagnate
z 0.5% potassium permagnate 95ml
z 3% sulfuric acid 5ml
z Solution should be made fresh.
Silver nitrate solution
z To 5ml of 10% aqueous silver nitrate, add strong ammonia drop by drop
until the precipitate which has formed initially is dissolved. Add 5ml of 3%
sodium hydroxide. Again add strong ammonia drop by drop till the
precipitate is completely dissolved. Add distilled water to make it 50ml and
keep it in a jar.
2% Oxalic acid
z Oxalic acid 2gm
z Distilled water 100ml
4% aqueous iron alum
z Ferric ammonium sulphate
z Distilled water 100ml
10% Formalin
z Formaldehyde 10ml
z Distilled water 90ml
0.2% Gold chloride
z Gold chloride 0.2%
z Distilled water 100ml
z Store in refrigerator

74 HISTOLOGY AND CYTOLOGY

Staining Methods to Demonstrate Special/ Specific Tissues MODULE
2% Sodium thiosulphate Histology and Cytology

z Sodiun thiosulphate 2gm

z Distilled water 100ml
Neutral red (acidified)
z Neutral red 1gm
z Distilled water 100ml Notes
z Glacial acitic acid 1ml
z Dissolve the dye in distilled water. Add the acid, mix, filter and store.

Procedure
1. Deparaffinize and bring the sections to water.
2. Oxidize in acidified potassium permagnate for 3 minutes.
3. Rinse in distilled water.
4. Decolorize with 2% oxalic acid for 1 minute.
5. Rinse in distilled water.
6. Put iron alum for 10 minutes.
7. Rinse in distilled water.
8. Put ammonical silver solution for 10 seconds.
9. Rinse in distilled water.
10. Immediately reduce with formalin for 2 minutes.
11. Wash in running tap water for 2 minutes.
12. Tone in 0.2% gold chloride for 2 minutes.
13. Rinse in distilled water.
14. Fix in 2% thiosulphate for 2 minutes.
15. Wash in water for 2 minutes.
16. Counter-stain with neutral red for 2 minutes.
17. Dehydrate, clear in xylene and mount in DPX.

Result
z Reticulin fibres black
z Nuclei red
Note
z All glassware should be cleaned thoroughly.

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 MODULE Staining Methods to Demonstrate Special/ Specific Tissues

Histology and Cytology z Silver solution should be made fresh.

z Step 12 should be omitted in liver sections.
z Counter-stain may be omitted in trefine biopsies.

Notes INTEXT QUESTION 11.1

1. ..................... stain is used for identifying collagen and muscle fibers in a
histological section
2. ..................... stain is used to demonstrate the presence of iron in tissues.
3. ..................... is the control used in Prussian blue stain.
4. ..................... staining is used to demonstrate the presence of argentaffin
granules.
5. ..................... is used to demonstrate calcium in paraffin sections.

WHAT HAVE YOU LEARNT

z Trichrome stain is used to identify the collagen and muscle fibres in a
histological section.
z Trichrome stain uses a combination of three different dyes
z Stain is used as a control in trichrome stain.
z Verheoff stain is used for identifying collagen and elastic tissue.
z Prussian blue stain is used to demonstrate the presence of iron in tissues
and hemosiderin positive is used as control.
z Argentaffin granules are demonstrating masson Fontana silver staining.
z Von-kossa stain is used to demonstrate calcium in paraffin sections.
z Muscle cross striations, fibrin and glial fibres can be demonstrated by
phospho-tungstic acid hematoxylin stain.

TERMINAL QUESTIONS
1. Explain Prussian blue staining technique.
2. Explain briefly masson Fontana silver staining.

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Staining Methods to Demonstrate Special/ Specific Tissues MODULE
Histology and Cytology

ANSWERS TO INTEXT QUESTIONS

11.1
1. Trichrome
2. Prussian blue
Notes
3. Hemosiderin positive tissue
4. Masson Fontana silver
5. Von – kossa stain

HISTOLOGY AND CYTOLOGY 77

Light Microscopy MODULE
Histology and Cytology

2
Notes
LIGHT MICROSCOPY

2.1 INTRODUCTION
Microscopes are instruments designed to produce magnified visual or
photographic images of objects too small to be seen with the naked eye. The
microscope must accomplish three tasks: produce a magnified image of the
specimen, separate the details in the image, and render the details visible to the
human eye or camera. This group of instruments includes not only multiple-lens
(compound microscopes) designs with objectives and condensers, but also very
simple single lens instruments that are often hand-held, such as a loupe or
magnifying glass.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the principle of light microscope
z explain the parts of a light microscope
z learn how to use a microscope.

2.2 LIGHT AND ITS PROPERTIES

Light radiates in all directions, with each ray traveling straight till infinity, unless
something interferes its path.
Wavelength (l)

Amplitude

Fig. 2.1: Light represented by a wave showing amplitude and wavelength.

HISTOLOGY AND CYTOLOGY 7

 MODULE Light Microscopy

Histology and Cytology

Amplitude refers to the strength of energy or brightness of light. When light
passes through any medium, the amplitude decreases depending upon the
medium.
Wavelength: The distance between the apex of one wave and the next is the
wavelength and measured in nanometers, and determines the color.
Retardation: Media through which light is able to pass, will slow down the
Notes speed of light (proportionate to density of medium).
Refraction: If light enters a medium (eg glass) at an angle, a deviation of
direction occurs

Image Formation
Focal point: Parallel rays entering a simple lens are brought together to a single
point called focal point, where a clear image will be formed.

Convex lens

Focal point

Focal length

Fig. 2.2: Parallel rays entering a curved lens are brought to a common focus.

Conjugate foci: Object placed at one end of lens will form a clear image on a
screen kept at other side of lens. Conjugate foci vary in position. If object is
nearer the lens, the image will be formed further away, at a greater magnification
and inverted. This “real” image is formed by objective lens of microscope. If
the object is placed within focal point of lens, image is formed on same side as
object, is enlarged, right way up and cannot be projected on a screen, this is the
“virtual image”. The eye piece of microscope forms this image.

Image Quality
As white light is composed of all spectral colors, different wavelengths will be
refracted to different extent. This lens defect is called chromatic aberration.
Spherical aberration is caused when light rays entering at a periphery are
refracted more than those entering the centre of lens. Both these faults can be
corrected by using combination of lenses and lens elements.

8 HISTOLOGY AND CYTOLOGY

Light Microscopy MODULE
Histology and Cytology
2.3 COMPONENTS OF A MICROSCOPE
Light source
Light source can be external or inbuilt. Dispersal of heat, collection of greatest
amout of light, direction and distance are carefully calculated by the designers
of microscope for greatest efficiency.

Eyepiece Notes

Coarse Adjustment Body Tube

Fine Adjustment Objectives

Stage
Arm Clamping Screw
Condenser
Joint
Mirror (Light
Source)
Base Condensor
Adjustment

Fig. 2.3: Microscope

Condensers
The purpose of condenser is to concentrate the light into the plane of the object.
The more the light at the specimen, better is its resolution. All condensers have
aperture diaphragm with which the diameter of the light beam can be controlled.

Object stage
It is a rigid platform with an aperture through which the light can pass. It supports
the glass slide. It allows controlled movement in two directions.

Objectives
They are the most important parts of microscope. The main task of objective is
to collect the maximum amount of light from the object, unite it and form a high
quality magnified real image. Magnifying powers of objectives are from 1:1 to
100:1.

Body tube
Body tube can be monocular, binocular and the combine photo-binocular (also
called trinocular). Binocular tubes have provision for inter-pupillary distance
adjustment, enabling each observer to adjust for his eyes.

HISTOLOGY AND CYTOLOGY 9

 MODULE Light Microscopy

Histology and Cytology Eyepiece

The final stage in optical path, the eyepiece’s function is to magnify the image
formed by the objective within the body tube, and present the eye with a virtual
image.

Use of the Microscope

Notes z Illumination should be centered.
z The condenser should be centered and in proper position.
z Objectives should be properly screwed.
z Optical parts should be clean and free from dust.
z Use oil only for oil immersion objective. After use, clean the oil objective
with lens tissue. Avoid use of xylene, alcohol or acetone. Eyepieces get dirty
by grease from eyelashes, clean them with lens paper.
z When changing slide, always lower the stage before removing the slide or
change objective lens to scanner view.
z Make sure the slide is the right way up.

INTEXT QUESTIONS 2.1

1. Parallel rays entering a simple lens are brought together to a single point
called
(a) Focal point (b) Optical point
(c) Conjugate (d) All of the above
2. Speed of light on entering a medium
(a) Increases (b) Decreases
(c) Remains constant (d) Variable
3. Choose the false statement
(a) Illumination of microscope should be centered
(b) Objectives should be properly screwed
(c) Use oil only for oil immersion objective
(d) When changing slide, always raise the stage
4. Instruments designed to produce magnified visual images of objects are
......................
5. Strength of energy or brightness of light is referred as ......................
6. Distance between apex of one wave and the next is ......................

10 HISTOLOGY AND CYTOLOGY

Light Microscopy MODULE
Histology and Cytology

WHAT HAVE YOU LEARNT

z Microscopes are instruments designed to produce magnified visual or
photographic images of objects too small to be seen by naked eye
z Light radiates in all directions, with each ray travelling straight till infinity,
unless something interferes its path Notes
z Amplitude refers to the strength of energy or brightness of light
z Wavelength is the distance between the apex of the wave to the next is the
wavelength and is measured in nanometers
z Media through which light is able to pass, will slow down the speed of light
is described as retardation
z Parallel rays entering a simple lens are brought together to a single point
called focal point
z Object placed at one end of lens will form a clear image on a screen kept
at other side of lens is described as conjugate lens
z Light source, Condensers, Object stage, Objectives, Body tubes and
Eyepieces are the components of microscope

TERMINAL QUESTIONS
1. Define amplitude and wavelength of light with diagram.
2. Define conjugate foci
3. Differentiate between chromatic and spherical aberration
4. Enumerate the different components of light microscope

ANSWERS TO INTEXT QUESTIONS

2.1
1. (a)
2. (b)
3. (d)
4. Microscope
5. Amplitude
6. Wavelength

HISTOLOGY AND CYTOLOGY 11

 MODULE Immunohistochemistry

Histology and Cytology

18
Notes
IMMUNOHISTOCHEMISTRY

18.1 INTRODUCTION
The gradual development of immunohistochemical methodologies over the past
decades has allowed the identification of specific or highly selective cellular
epitopes in formalin-fixed paraffin-embedded tissues with an antibody and
appropriate labeling system

OBJECTIVES
After reading this lesson, you will be able to:
z explain the principles of immunohistochemistry
z describe the methods of performing immunohistochemistry.

18.2 IMMUNOHISTOCHEMISTRY
Immunohistochemistry is a technique for identifying cellular or tissue constituents
(antigens) by means of antigen-antibody interactions, the site of binding can be
identified by direct labeling of the antibody or by use of a secondary labeling
method.

Antigen-Antibody binding
The amino acid side-chains of the variable domain of an antibody form a cavity
which is complementary to a single type of antigen like a lock and key. The
precise fit required explains the high degree of specificity seen in antigen-
antibody interaction.
Affinity: is the 3 dimensional fit of the antibody to its specific antigen and is
a measure of the binding strength between antigen and antibody.

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Immunohistochemistry MODULE
Avidity: is the functional combined strength of an antibody with its antigen. An Histology and Cytology
antibody against more than one epitope of an antigen will bind more strongly
to it.
Antibody specificity: is the characteristic of an antibody to bind selectively to
a single epitope or an antigen.
Sensitivity: is the relative amount of an antigen that a technique is able to detect.
Notes
Primary reagents
Polyclonal antibodies: they are produced by immunizing an animal with a
purified specific molecule (immunogen) bearing the antigen of interest. The
animal will mount a humoral response to the immunogen and the antibodies so
produced can be harvested from animal blood. The serum is polyclonal in nature
as it comprises of a mixture of antibodies to different epitopes present on the
antigen. Some of these antibodies may cross react with other molecules and
produce nonspecific staining.
Monoclonal antibodies: Hybridoma method is used to produce these antibodies
and it combines the ability of a plasma cells or transformed B lymphocytes to
produce a specific antibody with the in vitro immortality of a neoplastic
myeloma cell line. With the technique of cloning, this cell can be grown and
multiplied in cell culture to unlimited numbers and can produce large supply of
particular antibodies.
Labels: Enzymes are the most widely used labels in IHC, and incubation with
a chromogen using a standard histochemical method produces a stable, colored
reaction end-product suitable for the light microscope. Horseradish peroxidase
is the most widely used enzyme, and in combination with the most favored
chromogen, i.e. 3,3’- diaminobenzidine tetrahydrochloride (DAB) it gives a
crisp, insoluble, stable, dark brown reaction end-product.
Immunohistochemical Methods

Methods
There are numerous IHC staining techniques that may be used, the selection
should be based on parameters such as type of specimen, type of preparation
(frozen or paraffin section) and sensitivity required.
Traditional Direct technique: the primary antibody is conjugated directly to
the label. The conjugate may be either a fluorochrome or enzyme. The labeled
antibody reacts directly with the antigen. The technique is quick and easy to use
but provides little signal amplification and is less sensitive, so its used to

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 MODULE Immunohistochemistry

Histology and Cytology demonstrate immunoglobulins and complements in frozen sections of skin and
renal biopsies.
New direct technique (Enhanced polymer one step staining method):
available under the commercial name of EPOS. A large number of primary
antibodies and peroxidase enzymes are attached to a dextran polymer ‘backbone’,
hence increasing the signal amplification.
Notes Two step indirect technique: A labeled secondary antibody directed against the
immunoglobulin of the animal species in which the primary antibody has been
raised visualizes an unlabeled primary antibody. It is more sensitive than direct
technique.

Antigen retrieval
The demonstration of many antigens can be significantly improved by the
pretreatment with the antigen retrieval reagents that break the protein cross-links
formed by formalin fixation and thereby uncover hidden antigenic sites. It can
be done by enzymatic method and/or heat induced. The most popular enzymes
employed today are trypsin and protease. The enzymatic digestion breaks down
formalin cross-linking and hence the antigenic sites are uncovered.
Heat based antigen retrieval methods have brought great improvement in IHC.
The theories suggested for the role of heat pretreatment include: heavy salts act
as protein precipitant forming insoluble complexes with polypeptides. Another
theory is that heat mediated retrieval removes the weaker Schiff bases formed
during formalin fixation.
The different methods of heat based antigen retrieval include
1. Microwave antigen retrieval
2. Pressure cooker antigen retrieval
3. Steamer
4. Water bath
Microwave antigen retrieval with a non toxic citrate buffer at pH 6.0 has
demonstrated results equivalent to frozen sections. Most domestic microwave
ovens are suitable for antigen retrieval . Uneven heating and the production of
hot-spots have been reported, but using 400-600 ml of buffer in a suitably sized
container can minimize these problems.
Pressure cooker has been suggested as an alternative to microwave oven. Batch
variation and production of hot and cold spots in microwave can be overcome.
Pressure cooker is said to be more uniform in heating. Also the increased

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Immunohistochemistry MODULE
temperature (120°C) attained under pressure is an advantage in unmasking Histology and Cytology
antigens.
Buffers used for antigen retrieval:
z Sodium Citrate Buffer (10mM Sodium Citrate, 0.05% Tween 20, pH 6.0)
Tri-sodium citrate (dihydrate) 2.94 g
Distilled water 1000 ml Notes
Mix to dissolve. Adjust pH to 6.0 with 1N HCl.
Add 0.5 ml of Tween 20 and mix well. Store at room temperature for 3
months or at 4°C for longer storage.
z 1 mM EDTA, adjusted to pH 8.0
EDTA 0.37 g
Distilled water 1000 ml
Store at room temperature for 3 months.
z Tris-EDTA Buffer (10mM Tris Base, 1mM EDTA Solution, 0.05% Tween
20, pH 9.0)
Tris 1.21 g
EDTA 0.37 g
Distilled water 1000 ml (100 ml to make 10x, 50 ml to make 20x)
Mix to dissolve. pH is usually at 9.0.
Add 0.5 ml of Tween 20 and mix well. Store at room temperature for 3
months or at 4°C for longer storage.

IHC staining
All incubations should be carried out in a humidified chamber to avoid drying
of the tissue. Drying at any stage will lead to non-specific binding and ultimately
high background staining. A shallow, plastic box with a sealed lid and wet tissue
paper in the bottom is an adequate chamber, just as long as the slides are kept
off the paper and can lay flat so that the reagents don’t drain off. A good solution
is to cut a plastic serological pipette into lengths to fit your incubation chamber.
Glue them in pairs to the bottom of the chamber, with the 2 individual pipette
tubes of each pair being placed about 4.0 cm apart. This provides a level and
raised surface for the slides to rest on away from the wet tissue paper.
Dilutions of the primary and secondary antibody are listed on the datasheets or
are determined by testing a range. Adjust dilutions appropriately from the results
obtained. Adhere strictly to all incubation times in the protocol.

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 MODULE Immunohistochemistry

Histology and Cytology For enzymatic methods, horseradish peroxidase (HRP) or alkaline phosphatase
(AP) are the most commonly used enzymes. There are a number of chromogens
used with these enzymes.

Day 1
1. If using an HRP conjugate for detection, incubate the slides in 0.3% H2O2
Notes in Tris Buffered Saline (TBS) for 15 min
2. Wash the slides 2 x 5 minutes in TBS plus 0.025% Triton X-100 with gentle
agitation.
3. Block in 10% normal serum with 1% BSA in TBS for 2 hours at room
temperature.
4. Drain slides for a few seconds (do not rinse) and wipe around the sections
with tissue paper
5. Apply primary antibody diluted in TBS with 1% BSA
6. Incubate overnight at 4°C

Day 2
1. Rinse 2 x 5min TBS 0.025% Triton with gentle agitation.
2. For enzymatic detection (HRP or AP secondary conjugates): Apply enzyme-
conjugated secondary antibody to the slide diluted to the concentration
recommended by the manufacturer in TBS with 1% BSA, and incubate for
1 hour at room temperature.
3. Rinse 3 x 5min TBS.
4. Develop with chromogen for 10 min at room temperature
6. Rinse in running tap water for 5 min.
7. Counterstain (if required)
8. Dehydrate, clear and mount with DPX.

Fig. 18.1: Figure depicting various methods of antigen antibody interaction in IHC

118 HISTOLOGY AND CYTOLOGY

Immunohistochemistry MODULE
Histology and Cytology

INTEXT QUESTIONS 18.1

1. Technique used for identifying cellular constituents by means of antigen-
antibody interaction is ..................
2. The site of binding can be identified by .................. of the antibody
3. Three dimensional fit of the antibody to its specific antigen is .................. Notes
4. Functional combined strength of an antibody with its antigen is ..................
5. Characteristic of an antibody to bind selectively to a single epitope or an
antigen is ..................
6. Relative amount of an antigen that a technique is able to detect is called
..................

WHAT HAVE YOU LEARNT

z Immunohistochemistry is a technique for identifying cellular or tissue
constituents by means of antigen antibody interactions
z The site of binding can be identifying labeling of antibody
z Affinity is the three dimensional fit of antibody to its specific antigen
z Avidity is the functional combined strength of an antibody with its antigen
z Antibody specificity is the characteristic of an antibody to bind selectively
to a single epitope
z Sensitivity is the relative amount of an antigen that a technique is able to
detect
z Primary reagents are polyclonal antibodies, monoclonal antibodies
z Enzymes are sidely used lables in immunochemistry Horse radish peroxidase
is the most widely sued enzyme
z Numerous immunohistochemistry staining techniques may be used, and the
selection should be based on type of specimen, type of preparation and
sensitivity required
z Methods like traditional direct technique, new direct technique or enhanced
polymer one step staining method and two step indirect techniques are used
z Methods of antigen retrieval includes microwave, pressure cooker, streamer
and water bath antigen retrieval

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 MODULE Immunohistochemistry

Histology and Cytology

TERMINAL QUESTIONS
1. What is the principle of IHC?
2. What are the various methods of antigen detection in histopathology?
3. Enumerate the various methods of antigen retrieval.
Notes

ANSWERS TO INTEXT QUESTIONS

18.1
1. Immunohistochemistry
2. Labeling
3. Affinity
4. Avidity
5. Antibody specificity
6. Sensitivity

120 HISTOLOGY AND CYTOLOGY

Museum Techniques MODULE
Histology and Cytology

20
Notes
MUSEUM TECHNIQUES

20.1 INTRODUCTION
All teaching hospitals and colleges of Pathology have Museums which serve
many functions: permanent exhibition of common specimen for undergraduate
and postgraduate teaching purposes, illustrating specimens of rarity, permanent
source of histologic material and for gross and microscopic photography.

OBJECTIVES
After reading this lesson, you will be able to:
z explain the methods used in handling museum specimens
z describe the techniques of specimen preservation.

20.2 BASIC MUSEUM TECHNIQUES

Any specimens for museum are handled by following steps:
1. Reception
2. Preparation
3. Fixation
4. Restoration
5. Preservation
6. Presentation

Reception of the Specimen

Any specimen received in the museum should be recorded in a Reception book
and given a number followed by year (e.g. 32/2013). This number will stay with
specimen even after it is catalogued in its respective place. This number is

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 MODULE Museum Techniques

Histology and Cytology written on tie-on type label in indelible ink and is firmly attached or stitched to
the specimen. The reception book should contain all necessary information
about the specimen (clinical, gross and microscopic findings).

Preparation of the specimen

An ideal specimen is received fresh in unfixed state. However, it is mostly
obtained from pathology laboratory after being examined, thus will already be
Notes formalin fixed. If planning to use a specimen for museum, part of it can be kept
without disturbing for museum, e.g. in kidney it can be bisected and one half
kept aside for museum.

Fixation of the specimen

The objective of fixation is to preserve cells and tissue constituents in as close
a life-like state as possible and to allow them to undergo further preparative
procedures without change. Fixation arrests autolysis and bacterial decomposition
and stabilizes the cellular and tissue constituents. The fixatives used in museums
all over the world are based on formalin fixative technique, and are derived from
Kaiserling technique and his modifications. Kaiserling recommended that the
initial fixation be a neutral formalin (KI) solution and then transferred to a final
preserving glycerin solution (KIII) for long term display. Colour preservation
is also maintained with these solutions.

Kaiserling’s Technique
Fixation of specimen:
The specimen needs to be kept in a large enough container which can
accommodate specimen along with 3-4 times volume of fixative. Specimen is
stored in the Kaiserling I Solution for 1 month depending on the size of the
specimen. The specimen should not rest on bottom or an artificial flat surface
will be produced on hardening due to fixation.

Kaiserling I Solution:
Formalin 1L
Potassium acetate 45 g.
Potassium nitrate 25 g.
Distilled water Make up to 10 litres

Restoration of specimen
It is required to restore the specimens, as they lose their natural color on fixation.
The recommended method is the Kaiserling II method. It involves removing the

128 HISTOLOGY AND CYTOLOGY

Museum Techniques MODULE
specimen, washing it in running water and transferring to 95% alcohol for 10 Histology and Cytology
minutes to 1hour depending on the size of specimen. The specimen is then kept
and observed for color change for around 1- 1.5 hrs. After this step, specimen
is ready for preservation.

Kaiserling II Solution:
Alcohol 95% Notes
*Store specimen in this solution for 10 minutes to 1 hour depending on size of
specimen.
Rejuvenator Solution:
Pyridine 100 ml
Sodium hydrosulphite 100 gm
Distilled water 4 litres
*Formalin decreases the natural colour of the specimen. However, rejuvenator
solution restores the colour.

Preservation of specimen
The recommended solution for this step is Kaiserling III. This is the final solution
in which the specimen will remain for display. It is based on glycerine solution.

Kaiserling III Solution:

Potassium acetate 1416 g.
Glycerine 4 litres
Distilled water Make up to 10 litres
Thymol crystals added to prevent moulds.
*Leave solution to stand for 2 – 3 days before using to ensure proper mixing
of chemicals.
Add 1% pyridine as stabilizer. This solution acts as permanent fixative. This
solution easily turns yellowish and needs to be replaced to restore colour of the
specimen. The specimen will initially float to surface but later sink to bottom.

Presentation of the Specimen

Initially all museum specimens were mounted in cylindrical jars and sealed with
sheep bladder walls. Later they were replaced by rectangular glass jars. They

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 MODULE Museum Techniques

Histology and Cytology were better than cylindrical ones as the flat surfaces afforded a clear view of
specimens without any distortion. They are covered by rectangular glass plates.
These jars can be purchased readymade or assembled in museum itself, as per
need. Nowadays, Perspex jars are also available, which are lighter than glass jars.
However, they cannot be used to store specimens fixed in alcohol or methyl
salicylate as they react with plastics.

Notes Mounting the Specimens

To support the specimen within its jar, it is attached to the specimen plate or
rectangular bent glass rods. It can be done by tying the specimen with nylon
threads. Double knots should be made by threads, on the specimen surface.

Fig. 20.1: Museum specimens of cardiovascular system

TERMINAL QUESTIONS
1. Why do we need a museum?
2. What are the steps involved in mounting a specimen?
3. Describe the fixation of specimen.

130 HISTOLOGY AND CYTOLOGY

Tissue Processing MODULE
Histology and Cytology

7
Notes
TISSUE PROCESSING

7.1 INTRODUCTION
The technique of getting fixed tissues into paraffin is called tissue processing.
This describes the steps required to take animal and human tissues from fixation
to the state where it is completely infiltrated with a suitable wax i.e. paraffin wax
and can be embedded and ready for section cutting on microtome.

OBJECTIVES
After reading this lesson, you will be able to:
z define tissue processing

z describe its aim and method of processing.

Aim: To process the fixed tissue into a form in which it can be made into thin
microscopic sections.
Processing: The steps in this process are dehydration and clearing.
Dehydration: It is the process of removing water from tissues. It is important
because paraffin is not miscible with water. Dehydration is usually complete
when less then 3-4% of water remains in the tissues. Time required for this
depends on:
1. Permeability of tissues
2. Continuous rotation of fluid to prevent stagnation of fluid around tissues
3. Temperature
4. Vacuum applied
Dehydrants: Ethyl alcohol, Methyl alcohol, Butyl alcohol and Isopropyl
alcohol.
The most commonly used dehydrant is ethyl alcohol.

HISTOLOGY AND CYTOLOGY 35

 MODULE Tissue Processing

Histology and Cytology Alcohol Method: The tissues are passed through a series of progressively more
concentrated alcohol baths. Concentration of first alcohol bath depends on the
fixative and size and type of the tissue, e.g. delicate tissue needs lower
concentration of alcohol and smaller interval between two strengths of alcohol.
Usually 70% alcohol is employed as the first solution and100% as the last
solution. After about 40 tissues have passed through the first change of alcohol,
Notes it is discarded and all the other changes are brought one step lower. Absolute
alcohol at the end is always fresh.
Usually tissues are kept in each solution for 40 to 60 minutes.
Use of copper sulphate in final alcohol: A layer of anhydrous CuSO4 is placed
at the bottom of a dehydrating bottle or beaker and is covered with 2-3 filter
paper of approximate size to prevent staining of the tissue. Anhydrous CuSO4
removes water from alcohol as it in turn removes it from tissues.
Anhydrous CuSO4 is white in colour while the hydrated form is blue. Therefore,
it acts as an indicator for the presence of water.
Advantage of CuSO4 -
1. Rapid dehydration
2. Prolongs life of alcohol
3. Blue colouration of CuSO4 indicates that both alcohol and CuSO4 should
be changed.
Acetone - Acetone is clear colourless inflammable fluid which is miscible with
water, ethanol. It is used for complete dehydration. Four changes of acetone of
half an hour or two changes of one hour are given to achieve complete
dehydration of tissues.
Advantages
z Rapid action
z Easily removed by most clearing agents
z Less expensive
Disadvantages
z Highly volatile
z Causes shrinkage and brittleness of tissues
z Dissolves lipid more than ethanol
Clearing – Clearing is a process which leaves the tissues clear and transparent.
This term relates to the appearance of the tissues after the dehydrating agent has
36 HISTOLOGY AND CYTOLOGY
Tissue Processing MODULE
been removed. If the refractive index of the clearing agent is similar to the protein Histology and Cytology
of tissue the tissue becomes transparent. The end point of clearing can be noted
by the transparent appearance of the tissue. Thus clearing serves two purposes
1. Removes alcohol to make paraffin impregnation complete
2. Acts as solvent for the mounting media which renders the tissues transparent
and improves the refractive index, making microscopic examination easier.
Notes
Clearing Agents
z Xylene - It is colourless and most commonly used. Two changes of one hour
each are given to get the end point. Prolonged treatment hardens the tissues.
It is not preferred for brain tissue.

Other Clearing Agents

z Toluene
z Dioxane
z Cedarwood oil
z Cloroform
z Benzene
z Carbol-xylene - clears rapidly, it is kept reserved for material difficult to
clear.

7.2 INFILTRATION AND IMPREGNATION

After clearing, tissues are transferred to molten paraffin wax for filtration and
impregnation. During this process clearing agent diffuses out and molten wax
is infiltrated. The wax which has infiltrated in the tissue gets deposited. This
process is called impregnation. Routinely two changes are given in the wax to
get proper impregnation. The duration and number of changes required for
thorough impregnation of tissue depends on -

1. Size and type of tissues-Longer time is required for thicker tissues. Vacuum
reduces the time required for complete impregnation.
2. Clearing agent employed
3. Use of vacuum imbedding
Tissue processing may be performed manually or with the help of automated
tissue processor. Routinely 12 containers containing different solutions are used
for processing in the following order

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 MODULE Tissue Processing

Histology and Cytology z 10% formalin – container no 1, 2

z 50% alcohol – container no 3
z 90% alcohol – container no 4 & 5
z Absolute Alcohol – container no 6
z Acetone – container no 7 & 8
Notes z Xylene – container no 9 & 10
z Paraffin Wax – container no 11 & 12

INTEXT QUESTIONS 7.1

1. In tissue processing the tissues are impregnated into .....................
2. Steps in tissue processing are ..................... & .....................
3. Process of removing water from tissue is .....................
4. Most commonly used dehydrant in tissue processing is .....................
5. Usually ..................... alcohol is employed as first solution
6. ..................... is used as an indicator for the presence of water
7. Clearing is the process which leaves the tissues ..................... & .....................
8. Clearing serves two purposes namely ..................... & .....................
9. Most commonly used clearing agent is .....................
10. The process by which the infiltrated tissue gets deposited is called
.....................

7.3 TISSUE PROCESSING (PRACTICAL-1)

Tissue processing can be performed either manually or through automated tissue
processor. The device can handle larger number of tissues, process more quickly
and produces better quality outcome.
Two types of devices are available
z Tissue transfer or dip dunk
z Fluid transfer or enclosed
Advantages of automated tissue processor - Saves time, decreases human error,
effective fluid circulation, Temperature can be adjusted and vacuum/pressure
can also be incorporated.

38 HISTOLOGY AND CYTOLOGY

Tissue Processing MODULE
Tissue Transfer Type Histology and Cytology

The machine consist of a time clock, a circular superstructure that contains

basket carrier, a receptacle basket and receptacles (stainless steel or plastic
capsules), and a circular deck which holds the reagent beakers and plastic baths.
Small blocks of tissue are enclosed in the perforated capsules. These capsules
are placed in the basket which in turn is attached to one of the yokes in the
superstructure, while it is in the raised position. When the superstructure
Notes
descends the basket is immersed in the first solution and other reagent beakers
are covered preventing evaporation of reagents. To move the basket from one
reagent to the next the entire superstructure ascends and descends at scheduled
intervals controlled by the time clock. During immersion the basket rotates so
the infiltration of fluid into the tissues is optimum. The entire process takes about
16 hours. The machine is started in the evening so that the process is complete
in the morning,and embedding is done.

Fig. 7.1: Automated Tissue Processor

Enclosed Type
In this type of tissue processor the tissues remain in one container but reagents
get changed at scheduled interval.

Manual
In this process the tissue is changed from one container of reagent to another
by hand.

HISTOLOGY AND CYTOLOGY 39

 MODULE Tissue Processing

Histology and Cytology

Notes

Fig. 7.2: Enclosed Type Tissue Processor

Advantages
z Can be used when the number of tissue blocks is limited
z Non-availability of automated tissue processor

Disadvantages
z Difficult to use when large number of tissue blocks are to be processed
z Proper agitation of reagent not achieved
z More evaporation of reagents
z Process is tedious and requires constant attention

Precautions
1. Labels should be written with graphite pencil, India ink or typed.
2. The fluid used in complete dehydration and clearing tend to become
contaminated with fluid carried over from previous vat by the tissue. Every
alternate day daily the last solution is the series are replaced by fresh
solution of 100% alcohol, acetone and xylene and the previously used once
one moved forward while the first one is discarded. Other reagents are
changed twice a week or earlier with an average work load. It is far better
to change the reagents a day earlier than to have a precious surgical
specimen improperly infiltrated.

WHAT HAVE YOU LEARNT

z The technique of getting tissues fixed into paraffin is called tissue
processing so that thin microscopic sections can be achieved.

40 HISTOLOGY AND CYTOLOGY

Tissue Processing MODULE
z The main steps in processing are dehydration and clearing Histology and Cytology

z Dehydration is the process of removing water from tissues and time required
depends on permeability of tissues, temperature, vacuum applied and
continuous rotation of fluid to prevent stagnation of fluid around tissues.
z Most commonly used dehydrant is ethyl alcohol
z Anhydrous copper sulphate removes water from alcohol as it inturn removes
it from tissues and acts as a indicator for the presence of water Notes
z Acetone is used for complete dehydration
z Clearing is the process which leaves the tissues clear and transparent
z Clearing serves two purpose as it removes alcohol to make paraffin
impregnation complete and acts as a solvent for mounting media
z Xylene is the most commonly used clearing agent
z Impregnation is the process by which the infiltrated wax gets deposited

TERMINAL QUESTIONS
1. Explain dehydration process of tissue processing
2. Explain clearing process of tissue processing
3. List the advantages of copper sulphate

ANSWERS TO INTEXT QUESTIONS

7.1
1. Paraffin wax
2. Dehydration and clearing
3. Dehydration
4. Ethyl alcohol
5. 70%
6. Anhydrous copper sulphate
7. Clear & Transparent
8. Removes alcohol and acts as a solvent
9. Xylene
10. Impregnation

HISTOLOGY AND CYTOLOGY 41

Electron Microscopy MODULE
Histology and Cytology

19
Notes
ELECTRON MICROSCOPY

19.1 INTRODUCTION
Electron Microscopes were developed due to the limitations of Light Microscopes
which are limited by the physics of light to a resolution of about 0.2 micrometers.
In the early 1930’s this theoretical limit had been reached and there was a
scientific desire to see the fine details of the interior structures of organic cells
(nucleus, mitochondria...etc.). This required 10,000x plus magnification which
was just not possible using Light Microscopes. The Transmission Electron
Microscope (TEM) was the first type of Electron Microscope to be developed
and is patterned exactly on the Light Transmission Microscope except that a
focused beam of electrons is used instead of light to “see through” the specimen.
The electron microscope was invented in 1931 by Germans Ernst Ruska and
Max Knoll. Ernst Ruska later received Nobel Prize for his work in 1986.
Conventional transmission electron microscope (TEM) today can achieve a
resolution of 0.05nm.

OBJECTIVES
After reading this lesson, you will be able to:
z explain the principle of electron microscopy
z describe the tissue processing for electron microscopy.

19.2 TRANSMISSION ELECTRON MICROSCOPE

The original form of electron microscope, the transmission electron microscope
(TEM) is the direct counterpart of conventional light microscope. It uses a high
voltage electron beam to create an image. The electron beam is produced by an
electron gun, commonly fitted with a tungsten filament cathode as the electron

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 MODULE Electron Microscopy

Histology and Cytology source. The electron beam is accelerated by an anode typically at +100 keV (40
to 400 keV) with respect to the cathode, focused by electrostatic and
electromagnetic lenses, and transmitted through the specimen that is in part
transparent to electrons and in part scatters them out of the beam. When it
emerges from the specimen, the electron beam carries information about the
structure of the specimen that is magnified by the objective lens system of the
microscope. The spatial variation in this information (the “image”) may be
Notes viewed by projecting the magnified electron image onto a fluorescent viewing
screen coated with a phosphor or scintillator material such as zinc sulfide.
Alternatively, the image can be photographically recorded by exposing a
photographic film or plate directly to the electron beam.

Fig. 19.1: Transmission Electron Microscope

It is the direct counterpart of conventional light microscope. The most obvious
differences between TEM and light microscope are the: the ‘light’ source, the
form of the lenses and the manner in which image is formed.
The Electron beam: This is the source of ‘light’ in an EM, which can be
generated by thermionic emission from a tungsten filament using an electron
gun. Electrons are produced by passing a heating current through the filament.
In some microscopes, the beam can be generated by field emission.
Electromagnetic Lenses: The lenses in EM are electromagnetic coils. To focus
an electronic beam onto a given plane, the current passing through the coil is
changed. Thus the focal length of these so called lenses can be infinitely variable.
Image formation: In a light microscope, image formation occurs due differential
absorption of light rays. In EM, the image is formed partly by differential
absorption and partly by scattering.

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Electron Microscopy MODULE
Scanning Electron Microscope (SEM) Histology and Cytology

The SEM is an instrument that produces a largely magnified image by using

electrons instead of light to form an image. A beam of electrons is produced at
the top of the microscope by an electron gun. The electron beam follows a
vertical path through the microscope, which is held within a vacuum. The beam
travels through electromagnetic fields and lenses, which focus the beam down
toward the sample. Once the beam hits the sample, electrons and X-rays are
ejected from the sample. Detectors collect these X-rays, backscattered electrons, Notes
and secondary electrons and convert them into a signal that is sent to a screen
similar to a television screen. This produces the final image.

Fig. 19.2: Scanning Electron Microscope

Tissue Processing for EM:

To study the specimen with EM, a series of processing steps are required which
are similar but different to light microscopy. The steps involved are fixation,
dehydration, embedding, cutting and positive staining with heavy metals.

Specimen Handling & Fixation:

The specimen must be exposed to fixative as soon as possible after interruption
of blood supply. Slices of tissues about 1-2 mm thick should be cut and
transferred to a container containing fixative. The most popular method of

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 MODULE Electron Microscopy

Histology and Cytology fixation used is double fixation. It involves primary fixation in an aldehyde
followed by secondary (post) fixation in osmium tetroxide. Glutaraldehyde is
the most popular aldehyde for fixation of tissues for electron microscopy as it
reacts rapidly with proteins and stabilises structures by cross-linking before there
is any opportunity for extraction by the buffer . Hence more ground substance
of the cytoplasm (glycogen) and of the extracellular matrices is preserved. But,
glutaraldehyde alone is not an adequate fixative, since certain cell components
Notes especially lipids, are not fixed and may be extracted during dehydration,
therefore secondary fixation is required using osmium tetroxide. Depth of
penetration of glutaraldehyde is 2 - 3 mm / hour and of osmium tetraoxide is
1mm/hour.

Dehydration
The aim of dehydration is to remove all the free water in the fixed tissue and
replace it with a solution miscible with embedding medium. We usually use
organic solvents like methanol, ethanol or acetone. It starts with distilled water
to 40% ethanol and then through a series of increasing concentrations of ethanol
to 100% ethanol.
Protocol for dehydration in ethanol
1. 40% ethanol, 5 min.
2. 70% ethanol, 10 min.
3. 90% ethanol, 10 min
4. 100% ethanol, 3 x 10 min.
5. If ethanol is miscible with the embedding medium then tissue is directly
transferred to it. Otherwise, another transitional fluid may be required.
Epoxypropane is most commonly used transitional fluid.

Embedding Media
The embedding media for EM are resins, polyester resins and methacrylates. For
general electron microscopy epoxy resins have most properties required.

Epoxy resin

Characteristics

(a) Polyaryl ethers of glycerol with terminal epoxy groups.

(b) Transparent yellowish resins which range from viscous liquids to fusible
solids.
(c) Require addition of curing agents to convert them to a tough, extremely
adhesive and highly inert solid. Polymerization accomplished by the

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Electron Microscopy MODULE
addition of various bifunctional setting groups which link with the resin Histology and Cytology
to produce a three-dimensional structure.

Embedding
The embedding is carried out in polythene capsules or flat embedding moulds.
The capsules are filled with warm bubble-free raisin using a plastic pipette. No
air bubbles should be introduced in the medium. Labeling is done at this point.
Notes
It is best to write the identifier on a piece of paper and embed it along with tissue
using marking ink or pencil.

Sectioning
Getting an ultra-thin section is the pre-requisite for EM. It should be approximately
60 nm in thickness. Routine microtomes cannot produce such thin sections, thus
special microtome known as ultramicrotome is used which needs special
training. Glass knives or diamond knives are used to cut ultra-thin sections on
these ultra microtomes.

Applications of Electron Microscopy

1. Kidney biopsy interpretation
2. Skin biopsy interpretation
3. Viral and other infections
4. Inborn errors of metabolism
5. Tumor diagnosis

INTEXT QUESTIONS 19.1

1. Source of light in electron microscopy is ..................
2. The lenses in electron microscopy are ..................
3. In electron microscopy the image is formed by .................. & ..................
4. Surface topography of solid, unsectioned specimens is studied by ..................
5. Most popular method of fixation in electron microscopy is ..................
6. .................. is used for fixation in electron microscopy
7. .................. is the commonly used transitional fluid during dehydration
8. The thickness of section in electron microscopy should be approximately
..................

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 MODULE Electron Microscopy

Histology and Cytology

WHAT HAVE YOU LEARNT

z Transmission electron microscope is the direct counter part of conventional
light microscope
z Electron microscope involves the passing of high velocity, homogenous
electron beam through a thin enough specimen
Notes
z In electron microscopy the source of light is electron beam, lens are electron
magnetic coils & image formation occurs due to absorption & scattering
z Scanning electron microscope is used to study the surface topography of
solid, unsectioned specimens
z A series of steps namely fixation, dehydration, embedding, cutting &
positive staining with heavy metals are used for studying the specimen

TERMINAL QUESTIONS
1. What is the principle of EM?
2. What are the types of electron microscope?
3. What is the procedure for processing tissue for EM?
4. What are the applications of EM?

ANSWERS TO INTEXT QUESTIONS

19.1
1. Electron beam
2. Electromagnetic coils
3. Absorption & Scattering
4. Scanning electron microscopy
5. Double fixation
6. Gluteraldehyde
7. Epoxypropane
8. 60nm

126 HISTOLOGY AND CYTOLOGY

 MODULE Procedures for DNA, RNA and Mitochondria Demonstration

Histology and Cytology

16
Notes
PROCEDURES FOR DNA, RNA
AND MITOCHONDRIA
DEMONSTRATION

16.1 INTRODUCTION
Nucleoproteins are combinations of basic proteins and nucleic acids. The two
nucleic acids are deoxyribonucleic acid (DNA), which is mainly found in
nucleus and ribonucleic acid (RNA) which is located in the cytoplasm of cells,
mainly in the ribosomes. Both DNA and RNA molecules consist of alternate
sugar and phosphate groups with a nitrogenous base being attached to each sugar
group. The sugar in DNA is deoxyribose and in RNA it is ribose. The
demonstration of nucleic acid depends upon either the reaction of dyes with the
phosphate groups or the production of aldehydes from the sugars.

OBJECTIVES
After reading this lesson, you will be able to:
z explain the methods used in demonstrating nucleic acids
z describe the techniques and principles of the methods used.

16.2 DNA
The demonstration of DNA is either by Feulgen technique (which demonstrates
the sugar deoxyribose) or the methyl green-pyronin technique (where the
phosphates combine with basic dye methyl green at acidic pH). It can also be
demonstrated by fluorescent methods using acridine orange, but is considered

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Procedures for DNA, RNA and Mitochondria Demonstration MODULE
less reliable than the above mentioned methods. The definitive and most Histology and Cytology
sensitive technique is in situ hybridization.

16.3 FEULGEN TECHNIQUE

This technique involves mild acid hydrolysis with 1M hydrochloric acid at
60°C to break the purine-deoxyribose bond, the resulting exposed aldehydes are
then reacted with Schiff’s reagent to stain the DNA red-purple in color. Notes

Feulgen nuclear reaction for DNA

Fixation: Not critical but do not use Bouin’s fixative

Solutions
(a) 1 M hydrochloric acid
Hydrochloric acid (conc.) 8.5 ml
Distilled water 91.5 ml
(b) Schiff reagent
(c) Bisulfite solution
10% potassium metabisulfite 5 ml
1M hydrochloric acid 5 ml
Distilled water 90 ml
1. Bring all sections to water.
2. Rinse sections in 1M HCl at room temperature.
3. Place sections in 1M HCl at 60°C
4. Rinse in 1M HCl at room temperature, 1 minute.
5. Transfer sections to Schiff’s reagent, 45 minutes.
6. Rinse sections in bisulfate solution, 2 minutes, repeating twice again.
7. Rinse well in distilled water.
8. Counterstain if required in 1% light green, 2 minutes.
9. Wash in water.
10. Dehydrate through alcohols to xylene and mount.

Results
DNA red-purple
Cytoplasm green

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 MODULE Procedures for DNA, RNA and Mitochondria Demonstration

Histology and Cytology

Notes

Fig. 16.1: Mouse small intestine stained with Feulgen’s reaction and fast green
counterstain. DNA is stained a magenta color; the cytoplasm is stained a uniform green .

16.4 RNA
The method of choice for demonstrating RNA is the methyl green-pyronin
technique.

Methyl green-pyronin
Methyl green is an impure dye containing methyl violet. When methyl violet has
been removed by washing with chloroform, the pure methyl green appears and
is specific for DNA. Both dyes are cationinc, when used in combination methyl
green binds preferentially and specifically to DNA, and pyronin binds RNA.
Methyl green-pyroninmethod for RNA
Fixation: Carnoy preferred, but formalin acceptable.
Staining Solution: Methyl green pyronin Y
2% methyl green (chloroform washed) 9ml
2% pyronin Y 4 ml
Acetate buffer pH 4.8 23 ml
Glycerol 14 ml
Mix well before use.

Method
1. Take sections down to water.
2. Rinse in acetate buffer pH 4.8.
3. Place in methyl green-pyronin Y solution for 25 min.
4. Rinse in buffer.

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Procedures for DNA, RNA and Mitochondria Demonstration MODULE
5. Blot dry. Histology and Cytology

6. Rinse in 93% ethanol, then in absolute ethanol.

7. Rinse in xylene and mount.

Results
DNA green-blue
Notes
RNA red

Fig. 16.2: R.N.A. – (notably in plasma cell cytoplasm) – magenta. D.N.A. – green or
purplish green.

16.5 MITOCHONDRIA
Mitochondria are the cytoplasmic organelle found in variable numbers in all
animal cells. Large number of mitochondria in the cells can change the
appearance of cells. Mitochondria are considered the ‘power houses’ of the cell
as many of the energy producing biochemical reactions like oxidative
phosphorylation and Krebs cycle activity takes place in mitochondria.
Mitochondria can be demonstrated by electron microscopy, enzyme histochemistry
and histological methods however electron microscopy is the most satisfactory
method. Histopathological methods such as Altman’s technique for mitochondria
is simple and useful for demonstration of mitochondria.

Altman’s technique for mitochondria

Fixation
Champy’s fluid is usually recommended, Helly’s fluid works equally as well
Aniline-acid fuchsin – saturated solution of acid fuchsin in 5% aniline in
distilled water.

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 MODULE Procedures for DNA, RNA and Mitochondria Demonstration

Histology and Cytology Differentiator 1

Saturated alcohalic picric acid 10 ml
30% alcohol 40 ml

Differentiator 2
Saturated alcohalic picric acid 5 ml
Notes 30% alcohol 40 ml

Method
1. Take sections down to water.
2. Flood sections with aniline-acid fuchsin solution.
3. Gently heat the slide until steam rises and leave for 5 min.
4. Rinse in tap water.
5. Differentiate in solution 1 until the excess red stain is removed.
6. Completely differentiate in solution 2, controlling microscopically.
7. Dehydrate rapidly in two changes of absolute alcohal.
8. Clear in xylene and mount in DPX.

Results
Mitochondria red
RBC and nuclei red
Background tissue yellow

INTEXT QUESTIONS 16.1

1. Deoxyribonucleic acid is found in ....................
2. Ribonucleic acid is located in .................... of cells
3. Definite and most sensitive technique is ....................
4. .................... should not be used as fixation for DNA
5. .................... technique is the method of choice for demonstrating RNA
6. .................... is the preferred fixation for RNA demonstration
7. .................... is used for demonstration of mitochondria
8. In Methyl green pyronin technique the DNA appears .................... and RNA
appears ....................

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Procedures for DNA, RNA and Mitochondria Demonstration MODULE
Histology and Cytology

WHAT HAVE YOU LEARNT

z Nucleoproteins are combination of basic proteins and nucleic acids
z Two nucleic acids are deoxyribonucleic acid found in nucleus and ribonucleic
acid found in cytoplasm of cells
z Demonstration of nucleic acid depends upon either the reaction of dyes with Notes
phosphate groups or production of aldehydes from the sugars
z DNA is demonstrated by Feulgen technique and RNA by Methyl green
pyronin technique the most definite and sensitive technique is in-situ
hybridization
z Carnoy is preferred as fixative in methyl green pyronin technique for RNA
demonstration
z Mitochondria is demonstrated by Altman’s techniques and is best visualized
by electron microscopy

TERMINAL QUESTIONS
1. What are the components of nucleic acids?
2. What are the procedures used to detect DNA and RNA?
3. Describe the method used to detect mitochondria.

ANSWERS TO INTEXT QUESTIONS

16.1
1. Nucleus
2. Cytoplasm
3. In-situ hybridization
4. Bouin’s fixation
5. Methyl green pyronin
6. Carnoy
7. Altman’s technique
8. Green-blue & Red

HISTOLOGY AND CYTOLOGY 107

 MODULE Microtome

Histology and Cytology

9
Notes
MICROTOME

9.1 INTRODUCTION
A microtome (from the Greek mikros, meaning “small”, and temnein, meaning
“to cut”) is a tool used to cut extremely thin slices of material, known as sections.

OBJECTIVES
After reading this lesson, you will be able to:
z define Microtome
z describe the application of microtomes
z explain various microtomes
z describe microtome knife and its types.

9.2 MICROTOME
Various types of microtomes are available. Most commonly used microtome for
routine histopathology is rotary microtome.
The most common applications of microtomes are:
z Traditional Histology Technique: Tissues are hardened by replacing water
with paraffin. The tissue is then cut in the microtome at thicknesses varying
from 2 to 50 µm. From there the tissue can be mounted on a microscope
slide, stained with appropriate aqueous dye(s) after prior removal of the
paraffin, and examined using a light microscope.
z Cryosectioning Technique: Water-rich tissues are hardened by freezing
and cut in the frozen state with a freezing microtome or microtome-cryostat;
sections are stained and examined with a light microscope. This technique
is much faster than traditional histology (15 minutes vs 16 hours) and is

50 HISTOLOGY AND CYTOLOGY

Microtome MODULE
used in conjunction with medical procedures to achieve a quick diagnosis. Histology and Cytology
Cryosections can also be used in immuno histochemistry as freezing tissue
stops degradation of tissue faster than using a fixative and does not alter
or mask its chemical composition as much.
z Electron Microscopy Technique: After embedding tissues in epoxy resin,
a microtome equipped with a glass or gem grade diamond knife is used to
cut very thin sections (typically 60 to 100 nanometer). Sections are stained
Notes
with an aqueous solution of an appropriate heavy metal salt and examined
with a transmission electron microscope (TEM). This instrument is often
called an ultramicrotome. The ultramicrotome is also used with its glass
knife or an industrial grade diamond knife to cut survey sections prior to
thin sectioning. These sections are of 0.5 to 1 µm thickness and are mounted
on a glass slide and stained to locate areas of interest under a light
microscope prior to thin sectioning for the TEM. Thin sectioning for the
TEM is often done with a gem quality diamond knife.
z Botanical Microtomy Technique: Hard materials like wood, bone and
leather require a sledge microtome. These microtomes have heavier blades
and cannot cut as thin as a regular microtome.
Rotary Mictrotome - It is most commonly used microtome. This device
operates with a staged rotary action such that the actual cutting is part of the
rotary motion. In a rotary microtome, the knife is typically fixed in a horizontal
position.
A rotary action of the hand wheel actuate the cutting movement. Here the
advantage over the rocking type is that it is heavier and there by more stable.
Hard tissues can be cut without vibration. Serial sections or ribbons of sections
can easily be obtained. The block holder or block (depends upon the type of
cassette) is mounted on the steel carriage that moves up and down and is
advanced by a micrometer screw.
Auto-cut microtome has built in motor drive with foot and hand control. With
suitable accessories the machine can cut thin sections of paraffin wax blocks and
0.5 to 2.0 micrometer thin resin sections.

Advantages
1. The machine is heavy, so it is stable and does not vibrate during cutting.
2. Serial sections can be obtained.
3. Cutting angle and knife angle can be adjusted.
4. It may also be used for cutting celloidin embedded sections with the help
of special holder to set the knife.

HISTOLOGY AND CYTOLOGY 51

 MODULE Microtome

Histology and Cytology

Notes

Fig. 9.1: Rotary Microtome Fig. 9.2: Principle of sample movement for making
a cut on a rotary microtome

In the figure to the left, the principle of the cut is explained. Through the motion
of the sample holder, the sample is cut by the knife position 1 to position 2),
at which point the fresh section remains on the knife. At the highest point of the
rotary motion, the sample holder is advanced by the same thickness as the section
that is to be made, allowing for the next section to be made.
The flywheel in microtomes can be operated by hand. This has the advantage
that a clean cut can be made, as the relatively large mass of the flywheel prevents
the sample from being stopped during the sample cut. The flywheel in newer
models is often integrated inside the microtome casing. The typical cut thickness
for a rotary microtome is between 1 and 60 µm. For hard materials, such as a
sample embedded in a synthetic resin, this design of microtome can allow for
good “Semi-thin” sections with a thickness of as low as 0.5 µm.
Sledge Microtome is a device where the sample is placed into a fixed holder
(shuttle), the sledge placed upon a linear bearing, a design that allows for the
microtome to readily cut many coarse sections. Applications for this design of
microtome are of the preparation of large samples, such as those embedded in
paraffin for biological preparations. Typical cut thickness achievable on a sledge
microtome is between is 10 and 60 micron.

Fig. 9.3: Microtome Fig. 9.4: A cryomicrotome

52 HISTOLOGY AND CYTOLOGY

Microtome MODULE
Cryomicrotome Histology and Cytology

For the cutting of frozen samples, many rotary microtomes can be adapted to
cut in a liquid nitrogen chamber, in a so-called cryomicrotome setup. The
reduced temperature allows for the hardness of the sample to be increased, such
as by undergoing a glass transition, which allows for the preparation of semi-
thin samples. However the sample temperature and the knife temperature must
be controlled in order to optimise the resultant sample thickness
Notes
Ultramicrotome
A ribbon of ultrathin sections prepared by room temperature ultramicrotomy,
floating on water in the boat of a diamond knife used to cut the sections. The
knife blade is the edge at the upper end of the trough of water.

Fig. 9.5: Ultramicrotome

An ultramicrotome is a main tool of ultramicrotomy. It can allow for the

preparation of extremely thin sections, with the device functioning in the same
manner as a rotational microtome, but with very tight tolerances on the
mechanical construction. As a result of the careful mechanical construction, the
linear thermal expansion of the mounting is used to provide very fine control
of the thickness.
These extremely thin cuts are important for use with transmission electron
microscope (TEM) and Serial Block-Face Scanning Electron Microscopy
(SBFSEM), and are sometimes also important for light-optical microscopy. The
typical thickness of these cuts is between 40 and 100 nm for transmission
electron microscopy and often between 30 and 50 nm for SBFSEM. Thicker
sections up to 500 nm thick are also taken for specialized TEM applications or
for light microscopy survey sections to select an area for the final thin sections.
Diamond knives (preferably) and glass knives are used with ultramicrotomes.
To collect the sections they are floated on top of a liquid as they are cut and are
carefully picked up onto grids suitable for TEM specimen viewing. The
thickness of the section can be estimated by the thin-film interference colors of
reflected light that are seen as a result of the extremely low sample thickness.

HISTOLOGY AND CYTOLOGY 53

 MODULE Microtome

Histology and Cytology Vibrating microtome

The vibrating microtome operates by cutting using a vibrating blade, allowing
the resultant cut to be made with less pressure than would be required for a
stationary blade. The vibrating microtome is usually used for difficult biological
samples. The cut thickness is usually around 30-500 µm for live tissue and 10-
500 µm for fixed tissue.
Notes
Saw microtome
The saw microtome is especially for hard materials such as teeth or bones. The
microtome of this type has a recessed rotating saw, which slices through the
sample. The minimal cut thickness is approximately 30 µm, and can be made
for comparatively large samples.

Laser microtome
A conceptual diagram of laser microtome operation

Fig. 9.6: Laser microtome

The laser microtome is an instrument for contact free slicing. Prior preparation
of the sample through embedding, freezing or chemical fixation is not required,
thereby minimizing the artifacts from preparation methods. Alternately this
design of microtome can also be used for very hard materials, such as bones or
teeth as well as some ceramics. Dependent upon the properties of the sample
material, the thickness achievable is between 10 and 100 µm.
The device operates using a cutting action of an infra-red laser. As the laser emits
a radiation in the near infra-red, in this wavelength regime the laser can interact
with biological materials. Through sharp focusing of the probe within the
sample, a focal point of very high intensity, up to TW/cm2, can be achieved.
Through the non-linear interaction of the optical penetration in the focal region
a material separation in a process known as photo-disruption is introduced. By
limiting the laser pulse durations to the femtoseconds range, the energy

54 HISTOLOGY AND CYTOLOGY

Microtome MODULE
expended at the target region is precisely controlled, thereby limiting the Histology and Cytology
interaction zone of the cut to under a micrometre. External to this zone the ultra-
short beam application time introduces minimal to no thermal damage to the
remainder of the sample.

The laser radiation is directed onto a fast scanning mirror based optical system
which allows for three dimensional positioning of the beam crossover, whilst
allowing for beam traversal to the desired region of interest. The combination Notes
of high power with a high raster rate allows the scanner to cut large areas of
sample in a short time. In the laser microtome the laser-microdissection of
internal areas in tissues, cellular structures, and other types of small features is
also possible.

9.3 MICROTOME KNIFE

It is the important instrument used to cut uniform thin serial sections of the tissue.
Various types of knives are used with different microtomes. For routine purpose
wedge (C type) knife is used. It is plain on both sides. The size varies from 100
mm to 350 mm in length.

Microtome knives are made of good quality of high carbon or steel which is
tempered at the tip. Hardness of knife is essential to obtain good tissue sections.

Sharpening of microtome knife - To achieve good sections knife should be

very sharp. The knife is put in the knife back to sharpen. Knife can be sharpened
manually or by the use of automatic machine.

Honing - This is done to remove nicks and irregularity from the knife edge.
Coarse and fine honing is done using different abrasives.

Stropping - The purpose of stropping is to remove the “burr” formed during

honing and to polish cutting edge.

Other types of knives are diamond and glass knives. These knives are very
expensive and used for ultramicrotomy.

Disposable knife – Nowadays these microtome blades are used. Two types of
disposable blades are available.

1. Low profile blade - Usually used for cutting small and soft biopsies like
kidney and liver biopsies.

2. High profile blade-Used for any tissue like myometrium, breast tumor or
skin.

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 MODULE Microtome

Histology and Cytology Advantages

1. Time is not spent in sharpening, honing or stropping the knife.
2. Resistant to both corrosion and heat.
3. Hardness of blade can be compared with the steel knife.

Disadvantages
Notes
1. Relatively expensive
2. Disposable blades are not as rigid as steel knife:
Care of the Microtome Knife
z Store the knife in its box, when not in use.
z The knife should be cleaned with xylene before and after use.
z When knife is being stored for a long time, it should be smeared with grease
or good grade of light oil.
z Knife edge should not be touched.
z Knife edge should never be come badly nicked. It is advisable to use
separate knife for cutting hard issue like bone.
z The above points are important if re usable knife is being used.

Points to remember
1 For routine histopathology rotary microtome is used.
2 Ultramicrotome is used to cut semi-thin sections or ultrathin sections.
3 Traditional type of knife requires honing and stropping to smoothen the
cutting edge.
4 Disposable knives are expensive but do not need honing or stropping.
5 Knife edge is spoiled if properly decalcified tissue is not used.

INTEXT QUESTIONS 9.1

1. ...................... is used for cutting extremely thin slices
2. Most commonly used microtome is ......................
3. ...................... is an instrument for contact free slicing
4. ...................... knife is used in routine microtome
5. Nicks and irregularity from the knife edge is removed by ......................
technique
56 HISTOLOGY AND CYTOLOGY
Microtome MODULE
6. For polishing the cutting edge ...................... is used Histology and Cytology

7. ...................... disposable blade is used for cutting small and soft biopsies
8. ...................... disposable blade is used for tissues like myometrium
9. Microtome should be cleaned with ......................
10. Knife when stored for long time, should be smeared with ...................... or
...................... Notes

WHAT HAVE YOU LEARNT

z Microtome is a tool used to cut extremely thin slices of material
z Various types of microtome are available most commonly used microtome
for routine histopathology is rotary microtome
z Microtome are used in traditional histology, cryosectioning, electron
microscopy and botanical microtomy
z Rotary, Sledge, ultra, vibrating, saw, laser microtome are the different types
of microtome used
z Microtome knife is the important instrument to cut uniform thin serial
sections of the tissue.
z Microtome knife requires Honing and stropping for sharpening the edges
z Currently disposable knifes are commonly used. Low profile blade used for
cutting small & soft biopsies & high profile blade is used for any tissue
like myometrium
z Knife should be stored in its box and to be cleaned with xylene
z When knife is stored for a long time, it should be smeared with grease or
good grade of light oil.

TERMINAL QUESTIONS
1. What is a microtome? Write four types of microtomes and their uses.
2. What are the steps to sharpen the knife?
3. What are the applications of microtome?
4. Name two types of disposable microtome blades and their use.
5. What is the principle of rotary microtome?

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Histology and Cytology

ANSWERS TO INTEXT QUESTIONS

9.1
1. Microtome
2. Rotary microtome
Notes
3. Laser microtome
4. Wedge c type
5. Honing technique
6. Stropping
7. Low profile
8. High profile
9. Xylene
10. Grease or light oil

58 HISTOLOGY AND CYTOLOGY

 MODULE Embedding

Histology and Cytology

8
Notes
EMBEDDING

8.1 INTRODUCTION
Embedding is the process in which the tissues or the specimens are enclosed in
a mass of the embedding medium using a mould. Since the tissue blocks are very
thin in thickness they need a supporting medium in which the tissue blocks are
embedded. This supporting medium is called embedding medium. Various
embedding substances are paraffin wax, celloidin, synthetic resins, gelatine, etc.

OBJECTIVES
After reading this lesson, you will be able to:
z describe embedding
z explain embedding media
z describe types of moulds
z explain various devices for tissue embedding.

8.2 EMBEDDING
The choice of embedding media depends upon

z Type of microscope
z Type of microtome
z Type of tissue eg. hard tissue like bone or soft tissue like liver biopsy

Paraffin wax with a higher melting point (56 to 62oC) is used for embedding.
The molten wax is filtered inside the oven through a course filter paper into
another container. This will protect the knife edge.

42 HISTOLOGY AND CYTOLOGY

Embedding MODULE
Histology and Cytology
8.3 OTHER TYPES OF EMBEDDING MEDIA
z Carbowax: It is a water soluble wax. Therefore tissues are directly
transferred to water soluble wax after fixation and washing.
z Methacrylate: It is easily miscible with alcohol and gives a clear and hard
block when polymerised Polymerization takes place in the presence of a
catalyst. Any trace of water causes uneven polymerization and formation
of bubbles in the block around the tissue. Notes
z Epoxy Resin (Araldite): Epoxy polymers of araldite is used in higher
resolution work and to see greater details. Epoxy resins are used for electron
microscopy. Epoxy polymers of araldite differ from methcrylate in that they
are crosslinked causing the cured solid block of araldite to be insoluble in
any solvent. Longer filtration is required because the viscosity of resin is
greater than methacrylate.
For electron microscopy araldite is obtained as casting resinCY212,
ahardner DDSA and an amine accelerator, DMP (ditrimethylamino methyl
phenol) Blocks are suitably cured before sectioning for 48 to 60 hours at
60oC.
z Agar embedding: It is mainly used in double embedding. Multiple
fragments and friable tissue may be impregnated in one block when
sectioning on the cryostat. Another use of agar embedding is for FNAC
specimens.
z Celloidin media: Celloidin is a purified form of nitrocellulose. It is used
for cutting hard tissues.
z Gelatin: Its melting point is less than the melting point of agar. Gelatin may
be used when frozen sections are required on friable and necrotic tissues.

8.4 TYPES OF MOULDS

A variety of moulds are used for embedding. These may be LEUCKHARD
embedding moulds (L mould) paper blocks, plastic moulds. Most of the
laboratories use L moulds. L moulds are made up of metal, easy to procure,
reusable and may be adjusted to make different size of blocks. One limb of
the”L” is longer than the other. The two “Ls” are jointed to form a sides of the
rectangular box that act as a cast to make the mould.

Fig. 8.1: L moulds

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 MODULE Embedding

Histology and Cytology Plastic moulds: Most of the laboratories use plastic embedding rings now.
These are relatively inexpensive, convenient and support the block during
sectioning and are designed to fit it on the microtome. This eliminates the step
of mounting or attaching the block on a holder (metal or wooden holder).
1. Tissue-Tek System1 or Mark1 system: In this system plastic embedding
rings with stainless steel moulds allow rapid embedding and cutting of
tissues. In this system the blocks are stored with the plastic rings; the angle
Notes
does not change for further requirement of sections.
The disadvantage of this method is that the space required for storing is
more.

Fig. 8.2: Plastic Embedding Rings Fig. 8.3: Stainless Steel Moulds

2. Tissue-Tek system 2or Mark 2 system: The Mark 2 system has provided
a cassette to hold tissue during processing and has a stainless steel lid on
the plastic cassette. The cassette has a rough surface on one side of it with
a slope where the accession number or the marking is done using a
permanent marker.

Fig. 8.4: Plastic Embedding Cassettes

Advantages
z Since the cassette is processed with the tissues and afterwards used for
embedding, the writing has to be done once.

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Embedding MODULE
z Cassettes are thin so less wax is required. Histology and Cytology

z The space required for filing the blocks is less.

Disadvantages
z A special clamp has to be used in the microtome for this technique.
z The cassettes are shallow hence thin sections should be taken for processing.
Notes
8.5 PARAFFIN WAX ADDITIVES
Various substances can be added to paraffin wax in order to modify its
consistency and melting point to improve the efficiency during microscopy.
Additives increase the hardness of blocks. This helps in cutting thinner sections
at higher temperature. Stickiness of the medium is increased so better ribbons
can be obtained. However if larger quantities of additives are added, undesirable
side effects may be seen.

Commonly used additives

z Ceresin – It is hard white substance derived from mineral ozokerite. Its
melting point is between 61 to70o C. The addition of 0.3-0.5% is sufficient
to reduce the crystalline structure of paraffin wax.
z Bees’ wax - It is yellow substance with melting point of 64o C. This also
reduces the crystalline structure of the paraffin wax and improves the ribbon
quality.
z Bayberry wax - It is a vegetable wax and present in the peal of bayberry.
It is extracted from the peal of the fruit. Its melting point is 45° C.

Devices for tissue embedding

Devices designed specifically for tissue embedding are available for laboratories
in need of such equipment. These machines vary in size and design depending
on the number of samples they are designed to process. Some are designed for
specific embedding media, including proprietary compounds intended for
specific kinds of histopathology applications. Tissue embedding equipment
tends to be expensive. Manufacturers have sales representatives who can
provide information and advice when a lab is selecting new or replacement
equipment.

Tissue embedding machine

All the blocking steps can be performed with the help of tissue embedding
machine. The embedding machine contains the following parts -

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 MODULE Embedding

Histology and Cytology z Mould warmer, cassette bath, working surface warmer with a nozzle for
pouring the wax, forceps well and cold plate.
z The cold plate is of high efficiency refrigeration system having temperature
control ranging from different freezing points to 4 or 5 degree C. It can
occupy about 50-60 blocks.
z Large 3-5 litre capacity paraffin reservoir with adjustable temperature of 45-
Notes 75 degree C.
z Optional vacuum lids, which allows for vacuum infiltration of tissues.
z It has a forceps warmer convenient drain for excess wax.
z The embedding machines are available with many other features.

Fig. 8.5

Method of Embedding
1. Open the tissue cassette, check requisition form entry to ensure the correct
number of tissue pieces is present.
2. Select the mould; there should be sufficient room for the tissue with
allowance for at least a 2 mm surrounding margin of wax.
Leuckhart mould method-This is the traditional embedding method. The
“L moulds are adjusted according to the shape and size of the tissue.
Glycerine may be applied to the L pieces and also to the metal or glass
plate on which the moulds are placed for embedding. Simple glossed wall
or floor tiles may also be used in place of glass plate.
3. Fill the mould with paraffin wax.

46 HISTOLOGY AND CYTOLOGY

Embedding MODULE
4. Using warm forceps select the tissue, taking care that it does not cool in Histology and Cytology
the air; at the same time.
5. Place the tissue in the mould according to the side to be sectioned. This
side should be facing down against the mould. A small amount of pressure
may be used in order to have more even embedding.
6. Chill the mould on the cold plate, orienting the tissue and firming it into
the wax with warmed forceps. This ensures that the correct orientation is Notes
maintained and the tissue surface to be sectioned is kept flat.
7. Insert the identifying label or place the labelled embedding ring or cassette
base onto the mould
8. Add more paraffin into the mould to fill the cassette and mould.
9. Cool the block on the cold plate.
10. Remove the block from the mould.
11. Cross check block, label and requisition form.
Orientation of different tissue - During embedding the orientation of tissue is
important. Correct orientation of tissue in a mould is the most important step
in embedding. Incorrect placement of tissues may result in diagnostically
important tissue elements being missed or damaged during microtomy.
During embedding it is important to orient the tissue in a way that will provide
the best information to the pathologist. At the time of grossing, mark with India
ink may be put on the side of the tissue opposite that to be cut. The embedding
should be done according to the type of tissue. The requisition form should
always be read during embedding for proper orientation.

INTEXT QUESTIONS 8.1

1. ........................ is the process by which tissues or specimens are enclosed
in a mass of embedding medium
2. The supporting medium is called ........................ medium
3. ........................ is used for embedding
4. ........................ is used for electro microscopy
5. Agar embedding is used for ........................ & for ........................
6. ........................ is used for clotting hard tissues
7. ........................ increase the hardness of blocks
8. ........................ in a mould is most important step in embedding

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 MODULE Embedding

Histology and Cytology Some general considerations are as follows:

z Elongate tissues are placed diagonally across the block.
z Tubular and walled specimens such as vas deferens, cysts and gastrointestinal
tissues are embedded so as to provide transverse sections showing all tissue
layers.
z Tissues with an epithelial surface such as skin, are embedded to provide
Notes
sections in a plane at right angles to the surface (hairy or keratinized
epithelia are oriented to face the knife diagonally).
z Multiple tissue pieces are aligned across the long axis of the mould, and
not placed at random.
Incorrect placement of tissues may result in diagnostically important tissue
elements being missed or damaged during microtomy. In circumstances where
precise orientation is essential, tissue should be marked or agar double
embedded. Usually tissues are embedded with the surface to be cut facing down
in the mould.

Elongate Tissue Skin Tissue

Multiple Tubular or Cystic

Fig. 8.6

WHAT HAVE YOU LEARNT

z Embedding is the process in which tissues or specimens are enclosed in a
mass of the embedding medium using a mould
z Embedding medium are supporting medium into which the tissue block are
embedded

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Embedding MODULE
z Various embedding substances such as paraffin wax, celloidin, synthetic Histology and Cytology
resins, gelatine are used depending the type of microscope, type of
microtome, type of tissue.
z Epoxy resin is used for electron microscopy
z Agar embedding is used in double embedding and FNAC specimens
z Celloidin media is used for cutting hard tissues
Notes
z Gelatin is used when frozen sections are required on friable tissues
z A variety of moulds are used for embedding. There may be L moulds or
plastic moulds
z Various substances can be added to paraffin wax in order to modify its
consistency and melting point to improve efficiency during microtomy
z Additives increase the hardness of block
z Correct orientation of tissue in a mould is the most important steps in
embedding

TERMINAL QUESTIONS
1. Define embedding
2. Explain the types of embedding media
3. Explain the types of moulds

ANSWERS TO INTEXT QUESTIONS

8.1
1. Embedding
2. Embedding
3. Paraffin wax
4. Epoxy resins
5. Double embedding & FNAC
6. Celloidin media
7. Additives
8. Correct orientation of tissue

HISTOLOGY AND CYTOLOGY 49

 MODULE Morphology of Organs

Histology and Cytology

31
Notes
MORPHOLOGY OF ORGANS

31.1 INTRODUCTION
Tissue is a cellular organizational level intermediate between cells and a
complete organism. A tissue is an ensemble of similar cells from the
same origin that together carry out a specific function. Organs are then formed
by the functional grouping together of multiple tissues

OBJECTIVES
After reading this lesson, you will be able to:
z Enumerate various types of tissues of the human body
z Describe structure of various tissues of the human body

31.2 TYPES OF TISSUES

Following types of tissues make up all organs of the body:
A. Epithelium
B. Connective tissue-supporting tissue
C. Muscle-striated, smooth and cardiac
D. Nervous tissue
E. Blood-It is found in blood vessles, which are part of connective tissue.

A. Epithelium
Epithelial tissue covers the whole surface of the body. It is made up of cells
closely packed and ranged in one or more layers. This tissue is specialized to
form the covering or lining of all internal and external body surfaces. Epithelial

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Morphology of Organs MODULE
tissue that occurs on surfaces on the interior of the body is known as Histology and Cytology
endothelium. Epithelial tissue, is usually separated from the underlying tissue
by a thin sheet of connective tissue called as basement membrane. The basement
membrane provides structural support for the epithelium and also binds it to
neighboring structures.
Types of Epithelial Tissues. It can be divided into two types according to
location. Notes
1. Covers the external surface and line all the body cavities and tubes.
2. Secretory; found in glands.
Epithelial tissue can be divided into two groups depending on the number of
layers of which it is composes. Epithelial tissue which is only one cell thick is
known as simple epithelium. If it is two or more cells thick such as the skin,
it is known as stratified epithelium.

Simple epithelium
Simple epithelium can be subdivided according to the shape and function of its
cells.
z Squamous (pavement) epithelium
Squamous cells have the appearance of thin, flat plates. The shape of the
nucleus usually corresponds to the cell form. Squamous cells, for example,
tend to have horizontal flattened, elliptical nuclei because of the thin
flattened form of the cell. They form the lining of cavities such as the
mouth, esophagous, anus, uterine cervix and make up the outer layers
of the skin.

Nucleus
Cytoplasm

Cell membrane
Flat cell
Basal lamina

Fig. 31.1: Simple squamous epithelium

z Simple Cuboidal Epithelium

Cuboidal cells are roughly square or cuboidal in shape. Each cell has a
spherical nucleus in the centre. Cuboidal epithelium is found in glands and
in the lining of the kidney tubules as well as in the ducts of the glands.

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Histology and Cytology

Columnar cells
Cuboidal cell
Nucleus
Basal lamina
Fig. 31.2: Simple cuboidal epithelium
Notes
z Simple Columnar Epithelium
Columnar epithelial cells occur in one or more layers. The cells are
elongated and column-shaped. The nuclei are elongated and are usually
located near the base of the cells. Columnar epithelium forms the lining
of the stomach and intestines. Goblet cells (unicellular glands) are found
between the columnar epithelial cells of the colon. They secrete mucus, a
lubricating substance which keeps the surface smooth.

Columnar cells
Cytoplasm
Nucleus
Basal layer
Connective tissue

Fig. 31.3: Simple columnar epithelium

z Ciliated Columnar Epithelium

These are simple columnar epithelial cells, but in addition, they posses fine
hair-like outgrowths, cilia on their free surfaces. These cilia are capable of
rapid, rhythmic, wavelike beatings in a certain direction. Ciliated epithelium
is usually found in the air passages like the nose. It is also found in the
uterus and Fallopian tubes of females. The movement of the cilia propel
the ovum to the uterus.

Cilia
Columnar cells
Cytoplasm
Nucleus
Basal layer
Connective tissue

Fig. 31.4: Ciliated columnar epithelium

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z Glandular Epithelium Histology and Cytology

Columnar epithelium with goblet cells is called glandular epithelium.

Columnar and cuboidal epithelial cells often become specialized as gland
cells which are capable of synthesizing and secreting certain substances
such as enzymes, hormones, milk, mucus, sweat and saliva.

Columnar epithelium cells Notes

Globet cells which secrete mucus

Basal lamina

Connective tissue

Fig. 31.5: Glandular epithelium

z Stratified Epithelium.
Where body linings have to withstand wear and tear, the epithelia are
composed of several layers of cells and are then called compound or
stratified epithelium. The top cells are flat and scaly and it may or may not
be keratinised (i.e. containing a tough, resistant protein called keratin).
Human skin is an example of, keratinised, stratified epithelium. The lining
of the mouth cavity is nonkeratinising, stratified epithelium.

Horny epithelium cells

Cuboidal cells

Basal lamina

Connective tissue

Fig. 31.6: Stratified Epithelium

B. Connective Tissue
This is the most widespread tissue in the human body. Its function is primarily
to support, anchor and connect various parts of the body. Although connective
tissue exists in a number of forms, all types have three basic structural elements
cells, fibres and intercellular substance (ground substance).

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Histology and Cytology The most common cell type is fibroblast, which produces fibres and other
intercellular materials. The two most common types of fibres are: collagen
(collagenous) and elastic. Collagen fibres are for strength while elastic fibres
provide elasticity to the tissue. Both the cells and the fibres are embedded in the
intercellular substance. The consistency of this substance is highly variable
from gelatin-like to a much more rigid material.

Notes The proportions of the cells, fibres, and intercellular substance vary, depending
on a particular nature and function of the connective tissue. For example, a
strong connective tissue needs a greater proportion of the collagen fibres and
fewer cells eg. tendons and ligaments.Co nnective tissue composed of mostly
cells is loose and soft in consistency like adipose (fat).

Classification of Connective Tissue

I. Connective Tissue Proper – encompasses all organs and body cavities,
connecting one part with another and, equally important, separating one
group of cells from another.This includes adipose tissue (fat), areolar (loose)
tissue, and dense regular tissue.
II. Specialized Connective Tissues — this group includes cartilage, bone, and
blood. Cartilage and bone form the skeletal framework of the body.Blood
is circulated in the the vessles,made of connective tissues.
Muscles: There are three types of muscles in the body.
Smooth muscle: Muscle tissue that contracts without conscious control, having
the form of thin layers or sheets made up of spindle-shaped, unstriated cells with
single nuclei.It is present in the walls of the internal organs, such as the stomach,
intestine, bladder, and blood vessels.
Cardiac muscle: This type of muscle occurs only in heart. Its cells are joined
end to end. The resulting fibers are branched and interconnected in complex
networks. Each cell has a single nucleus. At its end, where it touches another
cell, there is a specialized intercellular junction called an intercalated disc, which
occurs only in cardiac tissue. Cardiac muscles work involuntarily and can
continue to function without being stimulated by nerve impulses.
Striated muscle: It is also called voluntary muscle, striped muscle, or skeletal
muscle.It is the most common of the three types of muscle in the body. Striated
muscles are attached to bones and produce all the movements of body parts in
relation to each other. Striated muscle is under voluntary control. Its multinucleated
fibers are long and thin and are crossed with a regular pattern of fine red and
white lines, giving the muscle its distinctive appearance and its name. These
cross striations are better seen with phosphotungstic acid hematoxylin stain.

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Histology and Cytology
Nucleus
Muscle fiber cell
Striations

Cardiac muscle cell Striations

Muscle fiber
Intercalated disk
Notes
Skeletal muscle
Nucleus

Smooth muscle cell Muscle fiber

Nucleus

Fig. 31.7: Types of muscle fibre

31.3 BONE
Bone is the basic unit of the human skeletal system and provides the framework
for and bears the weight of the body, protects the vital organs, supports
mechanical movement, hosts hematopoietic cells.
Cartilage and bone are specialized connective tissues and consist of cells and
extracellular matrix. The matrix of all connective tissues consists of fibres
(collagen, reticular, and elastic) and amorphous ground substance, which
contains proteoglycans and hyaluronic acid. The matrix is secreted by some of
the cells in connective tissues. In cartilage, it is chondroblasts and chondrocytes
that produce the matrix, while in bone, it is osteoblasts and osteocytes.
z Osteoprogenitor cells
They are pluripotent mesenchymal stem cells present in the vicinity of all
bony surfaces. On stimulation by growth factor they produce offspring that
differentiate into osteoblasts.
z Osteoblasts
They are located on the surface of bones. The cells synthesize, transport
and arrange protein of matrix. If osteoblasts become surrounded by newly
deposited organic matrix, they transform into osteocytes.
z Osteocytes
Osteocytes communicate with each other and with other cells on the bone
surface via an intricate network of cytoplasmic processes that traverse
tunnels in the matrix known as canaliculi.

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Histology and Cytology z Osteoclasts

These cells are responsible for bone resorption. They are derived from
hemopoetic progenitor cells. Mature osteoclasts are multinucleated.

Notes

Fig. 31.8: Histology of Bone

31.4 LIVER
The liver parenchyma is divided into thousands of small units called lobules.
A lobule is roughly hexagonal in shape, with portal triads at the vertices and a
central vein in the centre. In contrast, the hepatic acinus represents a unit that
is of more relevance to hepatic function because it is oriented around the afferent
vascular system.
The parenchymal cells of the liver are hepatocytes. These polygonal cells are
joined to one another in anastomosing plates, with borders that face either the
sinusoids or adjacent hepatocytes. Hepatocytes are in contact with blood in
sinusoids, which are distensible vascular channels lined with highly fenestrated
endothelial cells and populated with phagocytic Kupffer cells. The space
between endothelium and hepatocytes is called the Space of Disse which collects
lymph for delivery to lymphatic.

Fig. 31.9

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Morphology of Organs MODULE
Bile is secreted from the basal surface of hepatocytes, gets collect in channels Histology and Cytology
called canaliculi. These secretions flow toward the periphery of lobules and into
bile ductules and interlobular bile ducts, ultimately collecting in the hepatic duct
outside the liver. The hepatic duct is continuous with the common bile duct,
which delivers bile into the duodenum.

31.5 KIDNEY
Notes
Cut surface of kidney shows two parts ;the outer is cortex and inner part is
medulla.The two components of renal parenchyma are renal corpuscle and Loop
of Henle.

A. Renal Corpuscle
The renal corpuscle is the part of the kidney nephron in which blood plasma
is filtered. The renal corpuscle of each kidney nephron has two parts - they are
the Glomerulus, which is a network of small blood vessels called capillaries,
and the Bowman’s Capsule, which is the double-walled epithelial cup within
which the glomerulus is contained.
Within the glomerulus are glomerular capillaries.The afferent arterioles
bring blood into the glomerulus and the efferent arteriole drain blood out from
the glomerulus.
Capsular space is the area between the double-walls of the Bowman’s Capsule.
The cells that form the outer edges of the glomerulus form close attachments
to the cells of the inner surface of the Bowman’s Capsule.

B. Renal Tubule
The renal tubule is the part of the kidney nephron into which the glomerular
filtrate passes after it has reached the Bowman’s capsule. The first part of the
renal tubule is called the proximal convoluted tubule.
The water and solutes that have passed through the proximal convoluted tubule
(PCT) enter the Loop of Henle, which consists of two portions - first the
descending limb of Henle, then the ascending limb of Henle. The water (and
substances dissolved in it) pass from the renal cortex into the renal medulla, then
back to the renal cortex through Loop of Henle. When this fluid returns to the
renal cortex via the ascending limb of Henle, it passes into the distal convoluted
tubule (DCT).

The distal convoluted tubules of many individual kidney nephrons converge

onto a single collecting duct. Many collecting ducts join together to form

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Histology and Cytology several hundred papillary ducts. The contents of the papillary ducts drain into
the minor calces - the channels through which the fluid passes, via the major
calyx, into the centre of the kidney - called the renal pelvis.

Notes

Fig. 31.10

Gastrointestinal tract: It can be divided as

Upper and Lower human gastrointestinal tract
The upper gastrointestinal tract consists of the esophagus, stomach, and
duodenum

Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the small intestine,whole large
intestine and anus.
z Small Intestine - has three parts:
Doudenum
Jejunum
Ileum.
z Large Intestine: has three parts:
„ Caecum: The Vermiform appendix is attached to the caecum.
„ Colon: Includes the ascending colon, transverse colon, descending
colon and sigmoid colon.
„ Rectum and anal canal.

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Morphology of Organs MODULE
Histology and Cytology
Gland (e.g. salivary, liver) Mesentery

Brunner's glands
Muscularis mucosa Crypt of Lieberkuhn gland

Submucosa Tubular gland

Circular muscle Villi

Notes
Longitudinal muscle
Mucosa
Serosa
Peritoneum

Fig. 31.11: Histology

General structure of the gut wall

The gastrointestinal tract shows four layers on histology with some differences
that reflect the specialization in functional anatomy. These layers are in the
following order:

z Mucosa
z Submucosa
z Muscular layer)
z Adventitia or serosa

Mucosa
The mucosa is the innermost layer of the gastrointestinal tract.
The mucosa is made up of three layers:
z Epithelium - innermost layer.
z Lamina propria - a layer of connective tissue. Unusually cellular compared
to most connective tissue
z Muscularis mucosae - a thin layer of smooth muscle.
In the esophagus, the epithelium is stratified, squamous and non-keratinising,
for protective purposes.
In the stomach it is simple columnar, and is organised into gastric pits and glands
to deal with secretion.The small intestine epithelium the is organised into plicae
circulares and villi, and the enterocytes have microvilli. . In the ileum there are
occasionally Peyer’s patches in lamina propria.

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Histology and Cytology The colon has simple columnar epithelium with no villi. There are goblet cells.
The appendix has a mucosa resembling the colon but is heavily infiltrated with
lymphocytes.

The ano-rectal junction shows a transition from simple columnar to stratified

squamous non-keratinising epithelium for protective purposes.

Notes
Submucosa
The submucosa consists of a dense irregular layer of connective tissue with large
blood vessels, lymphatics, and nerves branching into the mucosa and muscularis
propia. It contains Meissner’s plexus, an enteric nervous plexus, situated on the
inner surface of the muscularis .

Muscularis propia
The muscularis externa consists of an inner circular layer and a longitudinal
outer muscular layer.. The layers are not truly longitudinal or circular, rather the
layers of muscle are helical with different pitches. The inner circular is helical
with a steep pitch and the outer longitudinal is helical with a much shallower
pitch.

Between the two muscle layers are the myenteric or Auerbach’s plexus. This
controls peristalsis. Activity is initiated by the pacemaker cells (interstitial cells
of Cajal).

The thickness of muscularis propia varies in each part of the tract. In the colon,
for example, the muscularis externa is much thicker because the faeces are large
and heavy, and require more force to push along. The outer longitudinal layer
of the colon thins out into 3 discontinuous longitudinal bands, known as taeniae
coli (bands of the colon). This is one of the 3 features helping to distinguish
between the large and small intestine.

The pylorus of the stomach has a thickened portion of the inner circular layer:
the pyloric sphincter.

Adventitia/serosa
The outermost layer of the GI tract consists of several layers of connective tissue.

Intraperitoneal parts of the GI tract are covered with serosa. These include most
of the stomach, first part of the duodenum, all of the small intestine, caecum and
appendix, transverse colon, sigmoid colon and rectum. In these sections of the

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Morphology of Organs MODULE
gut there is clear boundary between the gut and the surrounding tissue. These Histology and Cytology
parts of the tract have a mesentery.

Notes

Fig. 31.12: Longitudinal (outside) and circular (inside) layers of smooth muscle

Stomach Small
Esophagus Large Intestine
Intestine

Fig. 31.13

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