Basic concepts of
Pathology
Dr. P.P. Mkwajapi
Tandabui Institute of health sciences and Technology
Learning Objectives
• By the end of this session, students are expected to be able
to:
 Define pathology
 Identify subdivisions of pathology
 Explain disease development
 Classify categories of diseases
Pathology
Definition
Pathology= ( ‘pathos’ + logos)
Pathos: means “suffering”
Logos: means “study.”
Pathology: Is the scientific study of structure and function of the body in
disease.
“
the scientific study of disease”
It mainly focuses on the study of the structural and functional changes in cells, tissues,
and organs in disease
Subdivisions of Pathology
Depending upon the species studied, there are various disciplines of pathology such
as;
• Human pathology
• Animal pathology
• Plant pathology
• Veterinary pathology
• Poultry pathology etc.
• Comparative pathology deals with the study of diseases in animals in
comparison with those found in man
Subdivisions of Pathology
Human pathology is the largest branch of pathology
It is conventionally divided into

General pathology

Which deals with general principles of disease i.e. is concerned with
the basic reaction of cells and tissue to abnormal stimuli that
underlies all diseases

Systemic pathology

Includes study of diseases pertaining to the specific organs and body
systems.
Subdivisions of Pathology…..
 The speciality of pathology has come to include the following
subspecialities:
1. HISTOPATHOLOGY. Used synonymously with anatomic pathology,
pathologic anatomy, or morbid anatomy.
• The study includes structural changes observed by naked eye examination
(gross or macroscopic changes) and the changes detected by light and
electron microscopy supported by numerous special staining methods
including histochemical and immunological techniques to arrive at the most
Histopatholoy/Anatomic pathology includes the following 3 main subdivisions

Surgical pathology which deals with study of tissues removed from the living
body.

Forensic pathology and autopsy work. This includes the study
of organs and tissues removed at post-mortem for medicolegal
work and for determining the underlying sequence and cause of
death.

Cytopathology includes study of cells shade off from lesions
(exfoliative cytology ) and fine needle aspiration cytology of
superficial and deep seated lesion for diagnosis.
2. HAEMATOLOGY. Haematology deals with the diseases of blood. It
includes laboratory haematology and clinical haematology
3. CHEMICAL PATHOLOGY. Analysis of biochemical constituents
of blood, urine, semen, CSF and other body fluids is included in this
branch of pathology
4. IMMUNOLOGY. Detection of abnormalities in the immune system
of the body comprises immunology and immunopathology
5. EXPERIMENTAL PATHOLOGY. This is defined as production of
disease in the experimental animal and its study. However, all the
findings of experimental work in animals may not be applicable to
human beings due to species differences
6.GEOGRAPHIC PATHOLOGY. The study of differences in
distribution of frequency and type of diseases in populations in different
parts of the world forms geographic pathology.
7. MEDICAL GENETICS. This is the branch of human genetics that
deals with the relationship between heredity and disease. There have
been important developments in the field of medical genetics e.g. in
blood groups, inborn errors of metabolism, chromosomal aberrations in
congenital malformations and neoplasms etc.
8. MOLECULAR PATHOLOGY. The detection and diagnosis of
abnormalities at the level of DNA of the cell is included in molecular
pathology.
• Recent advancements in molecular biologic techniques have resulted
in availability of these methods not only for research purposes but also
as a tool in diagnostic pathology
Disease Development
Disease
Definition:
This is loss of ease of body or abnormal function of any part of the body

It is the opposite of health, what is not healthy is diseased
Disease development………
The four(4) aspects of a disease process that form the core of
pathology are

Its cause or aetiology

The mechanisms of its development (pathogenesis)

The structural alterations induced in the cells and organs of the
body(morphologic changes)

The functional consequences of the morphologic changes (clinical
significance)
Disease Development….
Aetiology or Cause
• Knowledge or discovery of the primary cause remains the backbone
on which a diagnosis can be made, a disease understood or a
treatment developed
• There are two major classes of aetiologic factors

Intrinsic or genetic

Acquired/Environmental factor
Disease Development….
 Environmental Factors that can cause disease are;
1. Physical agents, among these are
• Trauma
• Radiations
• Extreme heat and cold
•
Electrical power
These agents apply excess physical energy to the body
2.Chemicals
With the use of an ever-increasing number of chemical agents such as drugs, in
industrial processes, and at home, chemically induced injury has become very
common. Their effects vary:
• Some act in a general manner, for example cyanide is toxic to all cells.
• Others act locally at the site of application, for example strong acids and caustics.
• Another group exhibit a predilection for certain organs, for example – the effect of
paracetamol and alcohol on liver.
• Many toxic chemicals are metabolized in liver and excreted in kidney, as a result,
these organs are susceptible to chemical injury.
3. Nutritional deficiency and excess
•
These arise as a result of poor supply, interference with
absorption, inefficient transport within the body or defective
utilization.
•
The effect may be of a general nature as in starvation or lack of
oxygen.
•
They may cause specific damage e.g. in vitamin deficiencies
•
Dietary excess (eg obesity) can be the cause of many systemic
diseases such as cardiac diseases, high blood pressure, type 2
diabets
 Environmental Factors………….
4. Infections
•
and infestations
viruses, bacteria, fungi, protozoa and metazoan all cause
diseases.
•
They may do so by causing cell destruction directly as in
virus infections (for example poliomyelitis) or protozoal
infections (for example malaria).
•
However, in others the damage is done by toxins elaborated
by the infecting agent as in diphtheria and tetanus.
•
Like chemicals, they may have a general effect or they may
5.
Immunological factors
• The immune process is essential for protection against micro-organisms and parasites.
• However, the immune system can be abnormal which can lead to diseases.
The abnormalities of the immune system include:
A. Hypersensitivity reaction
• This is exaggerated immune response to an antigen. For example, bronchial asthma can
occur due to exaggerated immune response to the harmless pollen.
B. Immunodeficiency
• This is due to deficiency of a component of the immune system which leads to increased
susceptibility to different diseases. An example is AIDS
C. Autoimmunity
• This is an abnormal (exaggerated) immune reaction against the self
antigens of the host.
• Therefore, autoimmunity is a hypersensitivity reaction against the self
antigens.
• For example, type 1 diabetes mellitus is caused by autoimmune
destruction of the beta cells of the islets of Langerhans of the pancreas
6. Psychological
factors cause and influence disease process in several ways.

Psychological stress may lead to mental illness.

Their influence on the individual’s symptoms and reaction to
established somatic disease is apparent.

They are important components in disease caused by addiction,
e.g. alcohol and tobacco.

Psychogenic factors are causally related to diseases such as
hypertension, peptic ulcers, coronary artery thrombosis and
ulcerative colitis.
Disease Development….
 Genetic Factors
Essentially are the results of activities of single genes and groups of genes. Both
normal and abnormal gene influence susceptibility and resistance to disease
Normal genes




Susceptibility of fair (light) skin to damage e.g. skin cancer by the ultraviolet rays in sunlight. This is
due to lack of protective pigment – melanin.
The blood group A is associated with increased incidence of pernicious anaemia and gastric cancer.
Blood group B is associated with duodenal ulcer.
The human leucocytes antigen (HLA) is associated with susceptibility and resistance to infections
and also to the occurrence of autoimmune disorders.
The blood group Duffy negative confers resistance to infection by Plasmodium vivax.
Genetic Factors………
Abnormal genes



Mutation give rise to abnormalities of chromosomes and components
genes; the majority occur spontaneously without known cause, in some
cases radiation, chemical or infective agents are incriminated.
There are hereditary diseases where genetic abnormality directly
determines a disease, but most of the diseases are multifactorial having
elements of both genetic and environmental.
There is acquired specific genetic abnormality in stem cells, which
potentiate the development of malignant tumour.
Disease Development….
 Pathogenesis
• Refers to the sequence of events in the response of cells or
tissues to the aetiologic agent, from the initial stimulus to the
ultimate expression of the disease
• The study of pathogenesis remains on of the main domain of pathology
 Morphologic changes
• Refers to the structural alterations in cells or tissue that are
either characteristic of the disease or diagnostic of the
aetiologic process
Disease Development….
 Functional Derangements and Clinical Significance
The nature of the morphologic changes and their distribution in different
organs or tissues influence normal function and determine the clinical
features, course and prognosis of the disease.
All forms of organ injury start with molecular or structural alterations in cells.
Cell-cell and cell-matrix interactions contribute significantly to the
response to injury, leading collectively to tissue and organ injury which
are as important as cell injury in defining the morphologic and clinical
patterns of disease.
 Functional Derangements and Clinical Significance………
The failure of adaptation as seen in pathology may be due to
Inability to respond adequately i.e. in overwhelming infections
for which the body has no answer.
A disease is partly the result of an adaptive mechanism being
turned against the host instead of working to his benefit.



For example antibodies which aid to destruct harmful parasites such as bacteria,
they can cause disease because of host’s tissue become in anyway altered they
may themselves be mistaken as alien and invoke a destructive antibody
response, as various allergic disorders.
Classification of Disease
• Diseases may be classified from the etiological point of view as follows
a. Congenital diseases
• These diseases/defects exist at birth. Examples:
Hare-lip
Cleft palate
Congenital syphilis
b. Acquired diseases
i. Traumatic diseases
ii. Inflammatory diseases
iii.Degenerative diseases
iv.Deficiency diseases
v. Metabolic diseases e.g. Diabetes mellitus
vi.Neoplastic diseases e.g. New growth/tumors
…………….
Thanks for coming