INTRODUCTION TO PATHOLOGY

PATHOLOGY

• Pathology literally translates to the study of suffering (Greek pathos =

suffering, logos = study);
• As applied to modern medicine, pathology is the study of disease.
• Disease is the “state in which an individual exhibits an anatomical,
physiological, or biochemical deviation from the normal”. It may be
defined as an abnormal alteration of structure or function in any part of the
body.
FATHER OF MODERN PATHOLOGY:
RUDOLF VIRCHOW

• The founder of the field of cellular pathology.

• He stressed that most of the diseases of mankind
could be understood in terms of the dysfunction of
cells.
• In 1855, he proposed the axiom 'Omnis cellula e
cellula'—every cell arises from another cell.
 BRANCHES OF PATHOLOGY

• Pathology may be divided into following branches:

1. General Pathology
2. Systemic Pathology
3. Gross Pathology
4. Cellular Pathology
5. Surgical Pathology
6. Clinical Pathology
7. Immunopathology
 SUBDIVISIONS OF CLINICAL
PATHOLOGY

• Histopathology
• Cytopathology
• Haematology
• Microbiology
• Immunology
• Chemical Pathology
• Genetics
• Toxicology
• Forensic Pathology
 CLASSIFICATIONS OF THE DISEASE

• 1. Developmental – genetic, congenital.

• 2. Inflammatory – Trauma, infections, immune, etc.
• 3. Neoplastic – tumors or cancers
• 4. Degenerative – aging.
• 5. Metabolic.
• 6. Iatrogenic- Drug induced.
 4 ASPECTS OF DISEASE

• Pathology focuses on 4 aspects of disease:

• 1. Etiology: Cause of disease.
2. Pathogenesis: Mechanisms of development of disease.
3. Morphologic Changes: The structural alterations induced in cell and
tissues.
4. Clinical Manifestation: Functional results of the morphologic
changes, as observed clinically.
 ETIOLOGY

• Etiology refers to the underlying causes and modifying factors that are
responsible for the initiation and progression of disease.
• a. An etiologic agent is the factor (bacterium, virus, etc.) responsible for
lesions or a disease state.
b. Predisposing Causes of Disease: Factors which make an individual
more susceptible to a disease (damp weather, poor ventilation, etc.)
c. Exciting Causes of Disease: Factors which are directly responsible for a
disease (hypoxia, chemical agents…. etc.).
 PATHOGENESIS

• Pathogenesis refers to the mechanisms of development and progression of

disease, which account for the cellular and molecular changes that give rise to
the specific functional and structural abnormalities that characterize any
particular disease.
• Thus, etiology refers to why a disease arises and pathogenesis describes how a
disease develops
• Signs – Objective evidence of
the disease (e.g. Temperature,
blood pressure)
• Symptoms- Subjective evidence
of the disease that is
experienced or perceived by the
patient (e.g. Headache)
 CELLULAR RESPONSE TO STRESS AND
TOXIC INSULT

NORMAL CELL
• 1. Cellular adaptation (HOMEOSTASIS)
Physiologic ,Pathologic stress

• 2. Cell Injury CELLULAR

ADAPTATION
• 3. Cell death Injurious stimulus

Reversible Injury

Severe, progressive

Irreversible Injury

CELL
Necrosis Apoptosis
DEATH
 CELLULAR ADAPTATIONS TO STRESS

• Adaptations are reversible changes in the number, size,

phenotype, metabolic activity, or functions of cells in response
to changes in their environment.
• Physiologic adaptations usually represent responses of
cells to normal stimulation by hormones or endogenous
chemical mediators, or to the demands of mechanical stress
(in the case of bones and muscles).
• Pathologic adaptations are responses to stress that allow
cells to modulate their structure and function and thus
escape injury, but at the expense of normal function, such
as squamous metaplasia of bronchial epithelium in smokers
 CELLULAR ADAPTATIONS TO STRESS

• 1. HYPERTROPHY
- Hypertrophy is an increase in the size of cells resulting in an
increase in the size of the organ
- There are no new cells, just bigger cells containing increased
amounts of structural proteins and organelles.
- Hypertrophy can be physiologic or pathologic and is caused
either by increased functional demand or by growth factor or
hormonal stimulation
 CELLULAR ADAPTATIONS TO STRESS

• 1. HYPERTROPHY
• Example: Physiologic : Enlargement of the uterus during
pregnancy occurs as a consequence of estrogen stimulated
smooth muscle hypertrophy and smooth muscle
hyperplasia.
• Pathologic: The cardiac enlargement that occurs with Normal Cell
hypertension or aortic valve disease Hypertrophic
Cell
 CELLULAR ADAPTATIONS TO STRESS

• 2. HYPERPLASIA
-Hyperplasia is an increase in the number of cells in an organ that stems from
increased proliferation, either of differentiated cells or, in some instances, less
differentiated progenitor cells.
Hyperplasia can be physiologic or pathologic; in both situations, cellular
proliferation is stimulated by growth factors that are produced by a variety of cell
types
 CELLULAR ADAPTATIONS TO STRESS

• 2. HYPERPLASIA
-Examples :
Physiologic : The proliferation of the glandular epithelium of
the female breast at puberty and during pregnancy
Pathologic : Increased estrogenic stimulation causes
endometrial hyperplasia
NORMAL CELL

HYPERPLASIA
 CELLULAR ADAPTATIONS TO STRESS

• 3. ATROPHY
- Atrophy is shrinkage in the size of cells by the loss of cell
substance.
- Causes of atrophy include a decreased workload (e.g.,
immobilization of a limb to permit healing of a fracture),
loss of innervation, diminished blood supply, inadequate ATROPHIC CELL
nutrition, loss of endocrine stimulation, and aging (senile NORMAL CELL
atrophy).
- Cellular atrophy results from a combination of decreased
protein synthesis and increased protein degradation
 CELLULAR ADAPTATIONS TO STRESS

• 4. METAPLASIA
- Metaplasia is a change in which one adult cell type
(epithelial or mesenchymal) is replaced by another adult
cell type.
- Epithelial metaplasia is exemplified by the change that
occurs in the respiratory epithelium of habitual cigarette
smokers, in whom the normal ciliated columnar epithelial
NORMAL CELL
cells of the trachea and bronchi often are replaced by
stratified squamous epithelial cells METAPLASTIC
- The influences that induce metaplastic change in an CELL
epithelium, if persistent, may predispose to malignant
transformation.
 CELL INJURY

• Causes of cell injury:

1. Hypoxia and Ischemia - Hypoxia, which refers to oxygen

deficiency, and ischemia, which means reduced blood supply, are
among the most common causes of cell injury
2. Toxins -Potentially toxic agents are encountered daily in the
environment; these include air pollutants, insecticides, CO, asbestos,
cigarette smoke, ethanol, and drugs.
3. Infectious agents- All types of disease-causing pathogens,
including viruses, bacteria, fungi, and protozoans, injure cells.
 CELL INJURY

• Causes of cell injury:

4. Immunologic reactions- Examples are autoimmune

reactions against one’s own tissues, allergic reactions against
environmental substances, and excessive or chronic immune
responses to microbes
5. Genetic abnormalities- Genetic defects may cause cell
injury as a consequence of deficiency of functional proteins,
such as enzymes in inborn errors of metabolism, or
accumulation of damaged DNA or misfolded proteins, both of
which trigger cell death when they are beyond repair.
 CELL INJURY

• Causes of cell injury:

6. Nutritional imbalances- Protein–calorie insufficiency

among impoverished populations remains a major cause of
cell injury, and specific vitamin deficiencies
7. Physical agents –Trauma, extremes of temperature, radiation,
electric shock, and sudden changes in atmospheric pressure all
have wide-ranging effects on cells
8. Aging - Cellular senescence results in a diminished ability of
cells to respond to stress and, eventually, the death of cells and
of the organism
 CELL INJURY

• Reversible injury is the stage of cell injury at which the

deranged function and morphology of the injured cells can
return to normal if the damaging stimulus is removed
• The two main morphologic correlates of reversible cell
injury are cellular swelling and fatty change.
• Cellular swelling is commonly seen in cell injury
associated with increased permeability of the plasma
membrane.
• Fatty change is manifested by the appearance of
triglyceride containing lipid vacuoles in the cytoplasm. It is
principally encountered in organs that are involved in lipid
metabolism, such as the liver
 CELL DEATH

• When cells are injured they die by different mechanisms, depending on the
nature and severity of the insult:
1. Necrosis is a form of cell death in which cellular membranes fall apart, and
cellular enzymes leak out and ultimately digest the cell.
2. Apoptosis is regulated mechanism of cell death that serves to eliminate
unwanted and irreparably damaged cells, with the least possible host reaction,
characterized by enzymatic degradation of proteins and DNA, initiated by
caspases; and by rapid recognition and removal of dead cells by phagocytes
3. Necroptosis. This form of cell death is initiated by engagement of TNF
receptors as well as other, poorly defined triggers
4. Pyroptosis. This form of cell death is associated with activation of a cytosolic
danger-sensing protein complex called the inflammasome
 CELL DEATH

• Autophagy is an adaptation to nutrient deprivation in which cells digest their

own organelles and recycle them to provide energy and substrates. If the
stress is too severe for the process to cope with it, it results in cell death by
apoptosis
 CELL DEATH

• Cytoplasmic changes - Necrotic cells show increased

eosinophilia partly to increased binding of eosin to denatured
cytoplasmic proteins and partly to loss of basophilic
ribonucleic acid (RNA) in the cytoplasm
• Nuclear changes- Nuclear changes assume one of three
patterns, all resulting from a breakdown of DNA and
chromatin. Pyknosis is characterized by nuclear
shrinkage and increased basophilia; the DNA condenses
into a dark shrunken mass.
• The pyknotic nucleus can undergo fragmentation; this change
is called karyorrhexis.
• Ultimately, the nucleus may undergo karyolysis, in which the
basophilia fades because of digestion of DNA by
deoxyribonuclease (DNase) activity. In 1 to 2 days, the
nucleus in a dead cell may completely disappear.
 CAUSES OF NECROSIS

• 1. Ischemia or Anoxia

– loss of blood supply to an area leads to cell death due to

deprivation of their oxygen and nutrients, unless immediate
collateral circulation is brought from adjacent areas to satisfy their
metabolic needs.

- Cell death due to ischemia is known as Infarction, and is

manifested by a characteristic histologic appearance which is called
“Coagulation Necrosis”
 CAUSES OF NECROSIS

2. Physical Agents
– may act directly upon the cells or they may produce their effect
indirectly by rendering the blood supply inadequate, either by damage to
the blood vessels or increase in cellular metabolism such that blood supply
ultimately becomes inadequate.
• Trauma
• Extreme heat and cold
• Radiant energy
• Electrical energy
 CAUSES OF NECROSIS

3. Chemical Agents
– are most commonly exemplified by poisons, such as strong
acids and alkalies, also by bacterial toxins, parasitic poisons and plant
poisons.

4. Biologic Products
– bacteria may cause death of the cells by elaboration of toxic
products which may remain within the bacterial cell and are, known as
endotoxins.
 PATTERN OF TISSUE NECROSIS

A. According to Location/ Extent:

1. FOCAL NECROSIS- usually found as minute,
circumscribed lesions , confined to specific organ or
particular structure

2. MASSIVE NECROSIS - exemplified by gangrene, involves

whole or greater part of the organ.
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

1. Coagulative necrosis
- is a form of necrosis in which the underlying tissue
architecture is preserved for at least several days after death of cells in
the tissue
- Take on a firm texture
-Coagulative necrosis is characteristic of infarcts (areas of
necrosis caused by ischemia) in all solid organs except the brain.
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

2. Liquefactive Necrosis
– Characterized by digestion of dead cells, resulting in
transformation of the tissue into a liquid viscous mass by enzymes and
leukocytes.
- The necrotic material is frequently creamy yellow because of
the presence of dead leukocytes
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

3. Gangrenous Necrosis
- It usually refers to the condition of a limb (generally the lower
leg) that has lost its blood supply and has undergone coagulative necrosis
involving multiple tissue layers
- massive death of necrosis of tissue caused by combination of
ischemia and superimposed bacterial infection
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

4. Caseous Necrosis
- most often encountered in foci of tuberculous infection.
-Caseous means “cheeselike,” referring to the friable
yellow-white appearance of the area of necrosis
- Caseous necrosis is often surrounded by a collection of
macrophages and other inflammatory cells; this appearance is
characteristic of a nodular inflammatory lesion called a granuloma
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

5. Fat necrosis
- refers to focal areas of fat destruction, typically resulting from
the release of activated pancreatic lipases into the substance of the
pancreas and the peritoneal cavity.
- The released fatty acids combine with calcium to produce
grossly visible chalky white areas (fat saponification)
- On histologic examination, the foci of necrosis contain
shadowy outlines of necrotic fat cells surrounded by basophilic calcium
deposits and an inflammatory reaction.
 PATTERN OF TISSUE NECROSIS

B. According to Morphologic changes:

6. Fibrinoid Necrosis
- a special form of necrosis. Usually occurs in immune
reactions in which complexes of antigens and antibodies are
deposited in the walls of blood vessels
 INFLAMMATION

- Inflammation is a response of vascularized tissues to infections

and tissue damage that brings cells and molecules of host defense
from the circulation to the sites where they are needed, to eliminate
the offending agents
- From the Latin word “inflammare” – to set fire
-Protective response of the tissues of the body to irritation or injury
 FIVE CARDINAL SIGNS OF
INFLAMMATION:

• 1. Rubor( Redness) – due to arteriolar and capillary dilatation with

increased rate of blood flow towards the site of injury

• 2.Tumor (Swelling) – due to increased capillary permeability,

allowing the extravasation of blood fluid

• 3.Calor (Heat) – due to transfer of internal heat to the surface or site

of injury, brought about by increased blood content

• 4.Dolor (Pain) – due to pressure upon the sensory nerve by the

exudate or tumor

• 5.FunctioLaesa (Diminished function) – destruction of the

functioning units of the tissue
TRANSUDATE VS EXUDATE
 2 TYPES OF INFLAMMATION

• ACUTE INFLAMMATION
- It typically develops within minutes or hours and is of short
duration, lasting for several hours or a few days.
- Its main characteristics are the exudation of fluid and plasma proteins
(edema) and the emigration of leukocytes, predominantly neutrophils
(also called polymorphonuclear leukocytes).
- When acute inflammation achieves its desired goal of eliminating the
offenders, the reaction subsides and residual injury is repaired
 2 TYPES OF INFLAMMATION

• CHRONIC INFLAMMATION
- may follow acute inflammation or arise de novo.
- It is of longer duration and is associated with more tissue
destruction, the presence of lymphocytes and macrophages, the
proliferation of blood vessels, and fibrosis
 MORPHOLOGIC PATTERNS OF ACUTE
INFLAMMATION

• 1. Serous inflammation
- characterized by extensive outpouring of watery, low protein
fluid from either the blood serum or secretions of serosal mesothelial
cells
- fluid in serous inflammation is not infected by destructive
organisms and does not contain large numbers of leukocytes (which tend
to produce purulent inflammation, described later)
 MORPHOLOGIC PATTERNS OF ACUTE
INFLAMMATION

2. Fibrinous inflammation

- characterized by exudation of large amounts of fibrinogen and

precipitation of masses of fibrin, occurring in more severe acute
inflammation associated with marked endothelial damage

- A fibrinous exudate is characteristic of inflammation in the lining of

body cavities, such as the meninges, pericardium, and pleura.
 MORPHOLOGIC PATTERNS OF ACUTE
INFLAMMATION

3. Catarrhal inflammation

- affects mucous surfaces and characterized by hypersecretion of

mucosa with degenerative changes in the epithelium

4. Hemorrhagic inflammation

- characterized by admixture of blood and elements of exudates

 MORPHOLOGIC PATTERNS OF ACUTE
INFLAMMATION

5. Suppurative/ Purulent inflammation

- characterized by the production of pus, an exudate consisting of
neutrophils, the liquefied debris of necrotic cells, and edema fluid.
- The most frequent cause of purulent (also called suppurative)
inflammation is infection with bacteria that cause liquefactive tissue necrosis,
such as staphylococci; these pathogens are referred to as pyogenic (pus-
producing) bacteria.
- Pus, may be defined as a thick, creamy fluid composed of large
numbers of viable and necrotic polymorphonuclear leukocytes and necrotic
tissue debris that is partially liquefied by proteolytic digestion.
Abscesses are localized collections of pus caused by suppuration buried in a
tissue, an organ, or a confined space
FRESH TISSUE EXAMINATION

HISTOPATH LABORATORY
 METHODS OF FRESH TISSUE
EXAMINATION

• 1. Teasing or dissociation - is a
process whereby a selected tissue
specimen is immersed in a watch glass
containing isotonic salt solution, carefully
dissected or separated and examined
under the microscope, either unstained,
by Phase Contrast or Bright Field
Microscopy, or stained with differential
dye
 METHODS OF FRESH TISSUE
EXAMINATION

2. Squash preparation (Crushing) – is a

process whereby small pieces of tissues, not more
than 1 mm in diameter, are placed in a microscopic
slide and forcibly compressed with another slide or
with a coverglass.

• If necessary, a vital stain may be placed at the

junction of the slide and the coverglass and
allowed to be absorbed by the tissue through
capillary attraction.
 METHODS OF FRESH TISSUE
EXAMINATION

3. Smear preparation – is the process of examining

sections or sediments, whereby cellular materials are spread
lightly over a slide by means of a wire loop or applicator or
by making an opposition smear with another slide. This
technique is especially useful in cytological examination,
particularly for cancer diagnosis.
 METHODS OF FRESH TISSUE
EXAMINATION
3. Smear preparation
a. Streaking – with an applicator stick or platinum loop, the material is rapidly and
gently applied in a direct or zigzag line throughout the slide, attempting to obtain a
relatively uniform distribution of secretion. Too thin or thick smear have to be
avoided since they make the tissues unsuitable for examination.
 METHODS OF FRESH
TISSUE EXAMINATION

3. Smear preparation
b. Spreading – a selected portion of the material is
transferred to a clean slide and gently spread
moderately thick film by teasing the mucous strands
apart with applicator stick.

This method is a little more tedious than streaking, but

has the advantage of maintaining cellular
interrelationships of the material to be examined. It is
especially recommended for smear preparations of
fresh sputum and bronchial aspirates and also for thick,
mucoid secretions
 METHODS OF FRESH TISSUE
EXAMINATION

3. Smear preparation
c. Pull–apart – this is done by placing a drop of secretion or sediment upon one side and facing
it to another clean slide. The material disperses evenly over the surface of the two slides in the
opposite directions may be necessary to initiate the flow of materials. The two slides are then
pulled apart with a single uninterrupted motion, and the specimen placed under the microscope
for immediate examination, or applied with vital stain.
This is useful for preparing smears of thick secretions such as serous fluids, concentrated sputum,
enzymatic lavage samples from the gastro–intestinal tract and blood smears.
 METHODS OF FRESH TISSUE
EXAMINATION

3. Smear preparation
d.Touch preparation (impression smears) – is a
special method of smear preparation whereby the surface
of a freshly cut piece of tissue is brought into contact and
pressed on the surface of a clean glass slide allowing the
cells to be transferred directly to the slide for examination
by Phase Contrast Microscopy or after vital staining.
It has an added advantage in that the cells may be examined
without destroying their actual intercellular relationship,
and without separating them from their normal
surrounding.
 METHODS OF FRESH TISSUE
EXAMINATION

4. Frozen section – this method is normally

utilized when a rapid diagnosis of the tissue in
question is required and especially recommended
when lipids and nervous tissue elements are to be
demonstrated.
Very thin slices around 10 – 15u in thickness are
cut from a fresh tissue frozen on a microtome
with CO2 or on a Cyrostat, a cold chamber kept
at an atmospheric temperature of –10C to –20C
 PROCESSING OF TISSUES

• Solid structures and tissues must be preserved and carefully processed in

the following order:
• 1. Fixation
• 2. Dehydration
• 3. Clearing
• 4. Infiltration
• 5. Embedding
• 6. Trimming
• 7. Section – cutting
• 8. Staining
• 9. Mounting
• 10. Labeling