Introduction

Presented
By

D. Hallouma Amorha
Lecture(1) :‫اعداد‬
‫حلومة عمورة‬.‫د‬

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Histology:
study of the microscopic structure of biological
material and the ways in which components
are structurally and functionally related. It
Bridge between biochemistry, molecular
biology, physiology, disease processes and the
effects of diseases.

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1. What does histology primarily study?
• A. The molecular structure of DNA
• B. Microscopic structure of biological material
• C. Functions of organs in the body
• D. Treatment methods for diseases
Answer: B. Microscopic structure of biological material

2. Histology acts as a bridge between which fields?

• A. Biochemistry, molecular biology, and genetics
• B. Biochemistry, molecular biology, physiology, and disease
processes
• C. Anatomy, genetics, and pharmacology
• D. Pathology, anatomy, and epidemiology
Answer: B. Biochemistry, molecular biology, physiology, and disease
processes

3. Fill in the blank:

Histology links __________, molecular biology, physiology, and disease
processes.
**Histopathology:
Histopathology involves the clinical application
of histological methods to examine diseased
cells and tissues for diagnostic or prognostic
analysis of various medical conditions like
cancer and multi-organ diseases.

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1. What does histopathology focus on?
• A. Examining normal tissues
• B. Analyzing diseased cells and tissues
• C. Studying genetics of diseases
• D. Exploring biochemical pathways
Answer: B. Analyzing diseased cells and tissues

2. Which of the following is an application of histopathology?

• A. Treatment of diseases
• B. Prognostic analysis of conditions
• C. Physical therapy
• D. Development of vaccines
Answer: B. Prognostic analysis of conditions

3. Histopathology is useful for diagnosing which conditions?

• A. Allergies
• B. Cancer and multi-organ diseases
• C. Viral infections only
• D. Nutritional deficiencies
It is also used to identify pathogens like
bacteria, fungi, and parasites indicates the
presence of some heavy metals and other
toxins.

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**Histology:
is a field of biology and medicine dedicated to elucidating
tissue structure, function, and disease states.

The principle techniques of histology involve the use of various

chemical stains to interrogate tissue samples ranging from
single-celled organisms, plants, fungi, and animals, which are
optimized for unique targets.

**Pathology:
Study of disease, It focuses on the structural and functional
consequences of injurious stimuli on cells, tissues and organs

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Histochemistry:
means study of chemical nature of the tissue
components by histological methods. The cell
is the single structural unit of all tissues.
cytology :
The study of cell is called cytology.

A tissue is a group of cells specialized and

differentiated to perform a specialized
function.

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1. What does histochemistry study?
• A. Physical structure of tissues
• B. Chemical nature of tissue components
• C. Functional analysis of organs
• D. Genetic composition of cells
Answer: B. Chemical nature of tissue components

2. What is the basic structural unit of all tissues?

• A. Atom
• B. Cell
• C. Organ
• D. Protein
Answer: B. Cell

3. A tissue is defined as:

• A. A group of cells performing random tasks
• B. A group of cells specialized and differentiated for specific
functions
• C. A cluster of proteins forming structures
• D. A single cell performing all functions
Answer: B. A group of cells specialized and differentiated for specific
functions
 History
 1n 17th century ,Italian Marcello
Malpighi used microscopes to study
tiny biological entities; some regard
him as the founder of the fields of
histology and microscopic pathology.

 Malpighi analyzed several parts of

the organs of bats, frogs and other
animals under the microscope. While
studying the structure of the lung,
Malpighi noticed its membranous
alveoli and the hair-like connections
between veins and arteries, which he
named capillaries. His discovery
established how the oxygen breathed
in enters the blood stream and serves
the body.[
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1. Who is considered the founder of histology and microscopic pathology?
• A. Robert Hooke
• B. Anton van Leeuwenhoek
• C. Marcello Malpighi
• D. Galileo Galilei
Answer: C. Marcello Malpighi

2. What tool did Malpighi use to study tiny biological entities?

• A. Telescopes
• B. Microscopes
• C. Stethoscopes
• D. Thermometers
Answer: B. Microscopes

3. What structure in the lung did Malpighi observe?

• A. Bronchioles only
• B. Membranous alveoli
• C. Lymph nodes
• D. Trachea
Answer: B. Membranous alveoli

4. What term did Malpighi coin for the connections between veins and arteries?
• A. Capillaries
• B. Bronchi
• C. Valves
• D. Nerves
 In 19th century histology was an
academic discipline in its own right.
French anatomist Xavier
Bichat introduced concept
of tissue in anatomy

 in 1801 Meyer , 1819 Bichat

described twenty-one human
tissues, which can be subsumed
under the four categories currently
accepted by histologists. The

 1906 Nobel Prize in Physiology or

Medicine was awarded to
histologists Camillo
Golgi and Santiago Ramon y Cajal.
They had conflicting interpretations
of the neural structure of the brain
based on differing interpretations of
the same images.

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The histological specimen can be prepared as:
1. Whole mount
2. Sections
3. Smears.

1. Whole mounts
These are preparation entire animal eg.
fungus, parasite. These preparations should
be no more than 0.2-0.5 mm in thickness.

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2. Sections
The majority of the preparations in histology
are sections. The tissue is cut in about 3-5
mm thick pieces processed and 5 microns
thick sections are cut on a microtome.

Microtomes:
are special instruments which have automatic
mechanism for cutting very thin sections.

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3. Smears-
Smears are made from blood, bone marrow or
any fluid such as pleural or ascitic fluid.
These are immediately fixed in alcohol to
presence the cellular structures are then
stained.
Smears are also made by crushing soft tissue
between two slides or an impression smear in
made by pressing a clean slide in contact
with the moist surface of a tissue ,may be
stained for cytological examination

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The technician is responsible for

1. Specimen preservation.
2. Specimen labeling, logging & identification.
3. Preparation of the specimen to facilitate
their gross and microscopy.
4. Record keeping.

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describes the steps required to take an animal
or human tissue from fixation to the state
where it is completely infiltrated with a
suitable histological can be embedded ready
for section cutting on the microtome

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steps in tissue processing for paraffin
sections:
1.Obtaining a fresh specimen
2. Fixation
3. Dehydration
4. Clearing
5. Sectioning
6.Embedding
7.Staining
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Fresh tissue specimens will come from various
sources. It should be noted that they can
very easily be damaged during removal from
the patient or experimental animal.

It is important that they are handled carefully

and appropriately fixed as soon as possible
after dissection.

Ideally, fixation should take place at the site

of removal, perhaps in the operating theatre,
or, if this is not possible, immediately
following transport to the laboratory.
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Definition It is a complex series of chemical
events which brings about changes in the
various chemical constituents of cell like
hardening, however the cell morphology and
structural detail is preserved.

The specimen is placed in a liquid fixing agent

(fixative) such as processing formaldehyde
solution (formalin). This will slowly penetrate
the tissue causing chemical and physical
changes that will harden and preserve the
tissue and protect it against subsequent

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Unless a tissue is fixed soon after the removal
from the body it will undergo degenerative
changes due to autolysis and putrefaction

Principle of fixation- which produces

denaturation or coagulation of proteins so
that the semifluid state is converted into
semisolid state;

so that it maintains everything in vivo in

relation to each other. Thus semisolid state
facilitate easy manipulation of tissue

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If a fresh tissue in kept as such at room,
temperature it will become liquefied with a foul
odour mainly due to action of bacteria i.e.
putrefaction and autolysis so most aim of
fixation is:
1. To preserve the tissue in as lf like manner as
possible
2. To prevent postmortem changes like autolysis
and putrefaction. Autolysis is the lysis or
dissolution of cells by enzymatic action
probably as a result of rupture of lysosomes.
Putrefaction The breakdown of tissue by
bacterial action often with gas.

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 3. Preservation of chemical compounds and
microanatomic constituents so that further
histochemistry is possible.
4. Hardening : the hardening effect of fixatives
allows easy manipulation of soft tissue like
brain, intestines etc.
5. Solidification: Converts the normal semi
fluid consistency of cells (gel) to an
irreversible semisolid consistency (solid).
6. Optical differentiation - it alters to varying
degrees the refractive indices of the various
components of cells and tissues so that
unstained components
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7. Effects of staining - certain fixatives like
formaldehyde intensifies the staining
character of tissue especially with
haematoxylin

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1.Coagulation and precipitation

2. Penetration Fixation is done by immersing

the tissue in fluid containing the fixative.

Faster a fixative can penetrate the tissue

better it is penetration power depends
upon the molecular weight e.g. formalin
fixes faster than osimic acid.

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3. Solubility of fixatives - All fixatives should
be soluble in a suitable solvent, preferably in
water so that adequate concentrations can
be prepared

4. Concentration - It is important that the

concentration of fixative is isotonic or
hypotonic

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5. Reaction - Most fixatives are acidic. It may
help in fixation but can affect staining so has
to be neutralized

e.g.
formalin is neutralized by adding of calcium
carbonate. Amount of fixative The fixative
should be atleast 15-20 times the bulk of
tissue. For museum specimens the volume of
fixative is > 50 times.

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Note :
If the specimen is large then see that the
sections are made to make slices which have
a thickness of 1.5 cm so that fixative can
penetrate the tissue easily Reagents
employed as fixatives (simple fixatives)

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This lymph node was damaged by over-heating of the embedding center hot
plate.

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Thank you

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