General Pathology

General Pathology

LETTER TO THE STUDENT
Up to now in your studies, you
have been learning the normal features of human beings (i.e. anatomy, physiology, etc…).
Now it is time to introduce you to the abnormalities that can occur in humans – i.e. to
diseases. Pathology is a scientific study of diseases. In this year, you will learn the basic
mechanisms of diseases.
Pathology is divided into general & systemic pathology
General pathology covers the basic mechanisms of diseases whereas
systemic pathology covers diseases as they occur in each organ system.

That is, an acute inflammation in the skin has the same mechanisms & features as an acute inflammation of the meninges. The same principle applies to the other topics covered in general pathology
Therefore, if one knows general pathology well, one can apply this knowledge to diseases in the various organ systems

Hence, your general pathology knowledge will facilitate your understanding of systemic diseases (Systemic Pathology).
Therefore, the whole purpose of general pathology is to help you understand systemic diseases – i.e. Systemic Pathology. So, even though, you will understand the basic mechanisms of diseases common to various types of illnesses


The core aspects of diseases in pathology
Pathology is the science behind the cure and it is study of disease by scientific methods. The word pathology came from the
Latin words “patho” & “logy”. ‘Patho’ means disease and ‘logy’ means study, therefore
pathology is a scientific study of disease. Diseases may, in turn, be defined as an abnormal
variation in structure or function of any part of the body. Pathology gives explanations of a
disease by studying the following four aspects of the disease.
1. Etiology,
2. Pathogenesis,
3. Morphologic changes and
4. Functional derangements and clinical significance.

2. Pathogenesis

Pathogenesis means the mechanism through which the cause operates to produce the
pathological and clinical manifestations. The pathogenetic mechanisms could take place in
the latent or incubation period. Pathogenesis leads to morphologic changes.

3. Morphologic changes

The morphologic changes refer to the structural alterations in cells or tissues that occur
following the pathogenetic mechanisms. The structural changes in the organ can be seen
with the naked eye or they may only be seen under the microscope. Those changes that
can be seen with the naked eye are called gross morphologic changes & those that are
seen under the microscope are called microscopic changes. Both the gross & the
microscopic morphologic changes may only be seen in that disease, i.e. they may be
specific to that disease. Therefore, such morphologic changes can be used by the
pathologist to identify (i.e. to diagnose) the disease. In addition, the morphologic changes
will lead to functional alteration & to the clinical signs & symptoms of the disease


4. Functional derangements and clinical significance
The morphologic changes in the organ influence the normal function of the organ. By doing
so, they determine the clinical features (symptoms and signs), course, and prognosis of the
disease.
In summary, pathology studies:-
Etiology ???? Pathogenesis ???? Morphologic changes ???? Clinical features & Prognosis of all diseases.

Understanding of the above core aspects of disease (i.e. understanding pathology) will help
one to understand how the clinical features of different diseases occur & how their
treatments work. This understanding will, in turn, enable health care workers to handle &
help their patients in a better & scientific way. It is for these reasons that the health science
student should study pathology. In addition, the pathologist can use the morphologic
changes seen in diseases to diagnose different diseases. There are different diagnostic
modalities used in pathology. Most of these diagnostic techniques are based on
morphologic changes.

III. Diagnostic techniques used in pathology

The pathologist uses the following techniques to the diagnose diseases:
a. Histopathology
b. Cytopathology
c. Hematopathology
d. Immunohistochemistry
e. Microbiological examination
f. Biochemical examination
g. Cytogenetics
h. Molecular techniques
i. Autopsy


A. Histopathological techniques
Histopathological examination studies tissues under the microscope. During this study, the
pathologist looks for abnormal structures in the tissue.
Tissues for histopathological examination are obtained by biopsy. Biopsy is a tissue sample from a living person to identify the disease. Biopsy can be either incisional or excisional.
Once the tissue is removed from the patient, it has to be immediately fixed by putting it into adequate amount of 10% Formaldehyde (10% formalin) before sending it to the pathologist.

The purpose of fixation is:

1. to prevent autolysis and bacterial decomposition and putrefaction
2. to coagulate the tissue to prevent loss of easily diffusible substances
3. to fortify the tissue against the deleterious effects of the various stages in the
preparation of sections and tissue processing.
4. to leave the tissues in a condition which facilitates differential staining with dyes
and other reagents.
Once the tissue arrives at the pathology department, the pathologist will exam it
macroscopically (i.e. naked-eye examination of tissues).

Then the tissue is processed to make it ready for microscopic examination. The whole

purpose of the tissue processing is to prepare a very thin tissue (i.e. five to seven μm or
one cell thick tissue) which can be clearly seen under the microscope. The tissue is
processed by putting it into different chemicals. It is then impregnated (embedded) In paraffin, sectioned (cut) into thin slices, & is finally stained. The stains can be
Hematoxylin/Eosin stain or special stains such as PAS, Immunohistochemistry, etc...
The Hematoxylin/Eosin stain is usually abbreviated as H&E stain. The H&E stain is
routinely used. It gives the nucleus a blue color & the cytoplasm & the extracellular
matrix a pinkish color. Then the pathologist will look for abnormal structures in the tissue.
And based on this abnormal morphology he/she will make the diagnosis. Histopathology
is usually the gold standard for pathologic diagnosis.


B. Cytopathologic techniques
Cytopathology is the study of cells from various body sites to determine the cause or nature
of disease.
Applications of cytopathology:
The main applications of cytology include the following:
1. Screening for the early detection of asymptomatic cancer
For example, the examination of scrapings from cervix for early detection and prevention of
cervical cancer.
2. Diagnosis of symptomatic cancer
Cytopathology may be used alone or in conjunction with other modalities to diagnose tumors
revealed by physical or radiological examinations.
It can be used in the diagnosis of cysts, inflammatory conditions and infections of various
organs.
3. Surveillance of patients treated for cancer
For some types of cancers, cytology is the most feasible method of surveillance to detect
recurrence. The best example is periodic urine cytology to monitor the recurrence of cancer
of the urinary tract.

Advantages of cytologic examination

Compared to histopathologic technique it is cheap, takes less time and needs no anesthesia
to take specimens. Therefore, it is appropriate for developing countries. In addition, it is complementary to histopathological examination.
Cytopathologic methods
There are different cytopathologic methods including:
1. Fine-needle aspiration cytology (FNAC)
In FNAC, cells are obtained by aspirating the diseased organ using a very thin needle under
negative pressure. Virtually any organ or tissue can be sampled by fine-needle aspiration.
The aspirated cells are then stained & are studied under the microscope. Superficial organs
(e.g. thyroid, breast, lymph nodes, skin and soft tissues) can be easily aspirated. Deep
organs, such as the lung, mediastinum, liver, pancreas, kidney, adrenal gland, and
retroperitoneum are aspirated with guidance by fluoroscopy, ultrasound or CT scan. FNAC
is cheap, fast, & accurate in diagnosing many diseases.


2. Exfoliative cytology
Refers to the examination of cells that are shed spontaneously into body fluids or secretions.
Examples include sputum, cerebrospinal fluid, urine, effusions in body cavities (pleura,
pericardium, peritoneum), nipple discharge and vaginal discharge.
3. Abrasive cytology
Refers to methods by which cells are dislodged by various tools from body surfaces (skin,
mucous membranes, and serous membranes). E.g. preparation of cervical smears with a
spatula or a small brush to detect cancer of the uterine cervix at early stages. Such cervical
smears, also called Pap smears, can significantly reduce the mortality from cervical cancer.
Cervical cancer is the rare cancer in Iraqi women

C. Hematological examination

This is a method by which abnormalities of the cells of the blood and their precursors in the
bone marrow are investigated to diagnose the different kinds of anemia & leukemia.
D. Immunohistochemistry
This is a method is used to detect a specific antigen in the tissue in order to identify the type
of disease.
E. Microbiological examination
This is a method by which body fluids, excised tissue, etc. are examined by microscopical,
cultural and serological techniques to identify micro-organisms responsible for many
diseases.
F. Biochemical examination
This is a method by which the metabolic disturbances of disease are investigated by assay
of various normal and abnormal compounds in the blood, urine, etc.


G. Clinical genetics (cytogenetics),
This is a method in which inherited chromosomal abnormalities in the germ cells or acquired
chromosomal abnormalities in somatic cells are investigated using the techniques of
molecular biology.
H. Autopsy
Autopsy is examination of the dead body to identify the cause of death. This can be for
forensic or clinical purposes.

IV. The causes of disease

Diseases can be caused by either environmental factors, genetic factors or a combination of the two
.
A. Environmental factors
Environmental causes of disease are many and are classified into:
1. Physical agents
2. Chemicals
3. Nutritional deficiencies & excesses
4. Infections & infestations
5. Immunological factors
6. Psychogenic factors