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INTRODUCTION TO PATHOLOGY
PATH 303
General Pathology
4(3-2)
Dr. Temur Ahsan Khan
PATHOLOGY
Pathos (suffering or disease) logos (science)
 Pathology is the study of structural and functional
changes of body in disease, including changes in cell,
tissues, organs and body fluids.
 Pathology forms a bridge between basic studies of
Anatomy, Physiology, biochemistry and clinical subjects of
Medicine and Surgery

DISEASE


French word “Des” (away) “aise” (ease)
it is a condition in which the individual suffers
from discomfort i.e. not at harmony with its
environment.
Lesion
It is the abnormal structural or functional change in the
body as a result of disease and may be detected by
gross (necropsy), microscopic (histopathology) or
biochemical methods (clinical pathology).
PATHOGNOMONIC LESION
An alternation that indicates without doubt the cause of
a particular disease e.g. finding of Negri bodies in
rabies etc
PATHOGENESIS


It is a progressive development of a disease process
from its initiation to conclusion in recovery or death.
Disease is a dynamic process which progresses from
molecular or bio-chemical alternations to structural
(ultrastructural, microscopic and gross lesions) and to
functional changes which are seen as signs and
symptoms of disease.
Functional
Structural
Pathological
changes
Moderate
Time
D
IAGNOSIS
 It is the identification of disease through the clinical
examination and application of various laboratory
tests.
 A pathological diagnoses should include lesions,
etiology (cause) pathogenesis and clinical
consequences.
Prognosis
• It is the estimation of the clinician or pathologist
regarding the expected outcome of disease like favorable,
guarded or grave ete
Etiology



It is a study of the causes of disease.
An etiologic agent induces cell and tissue injury
leading to clinical manifestations of disease
There are numerous causes of disease which are
divided into
1.
2.
Exogenous (Environmental or extrinsic factors)
Intrinsic Internal defects
BIOLOGICAL AGENTS (INFECTIOUS
AGENTS, PATHOGENS,
MICROORGANISMS)

These are diverse group of biological agents,
ranging from a few nm to a few meters in size.
The disease producing biological agents mostly
have a parasitic mode of life and include prions,
viruses, chlamydia, rickettsia, mycoplasma,
bacteria, fungi, protozoa and metazoa.
CHARACTERISTICS OF
MICROBIOLOGICAL AGENTS
 Biological
associations and relationships.
 Commensals: coexistence without injury
or benefit
 Symbiotic: Mutually beneficial
coexistence.
Example: microflora and fauna in the
rumen and colon of herbivores and E.coli
in the gut of humans producing vit.K.
 Parasitic/Predators: causing morbidity
and mortality in the host (man and
animals)
PORTAL OF ENTRY IN THE BODY:
Lungs and mucociliary mechanisms
 Mouth and GIT. Gastric acidity
 Intact membranes
 Size of inoculum-MID 50 and MLD 50

HOST DEFENSE MECHANISMS.
Humoral- innate natural immunity, acquired
immunity, antibody formation.
 Cellular defense- Phagocytosis by neutrophils
and monocytes.

SURVIVAL OF MICROORGANISMS IN
THE BODY:
Spreading factor- Hyaluronidase
 Evasion of phagocytosis- capsule formation
 Sequestration-coagulase,collagenase,
organotropism

INTRACELLULAR LOCALIZATION
Facultative- Mycobacterium, Brucella,
Histoplasma, Nocardia, Toxoplasma, Theileria
 Obligate- Rickettsia, Viruses, Plasmodium.

HOW MICROORGANISMS CAUSE
DISEASE

Host factors- age, nutrition, immune status,
intercurrent disease, opportunistic infection,
predisposing factors
GENERAL MECHANISM OF DISEASE
PRODUCTION:
Dysfunction and death of host cells
 Release of endotoxins and exotoxins
 Induction of immune and inflammatory
responses causing injury and disease.

MECHANISMS OF VIRAL INJURY:
Host cell receptors
 Type- specific transcription factors
 Crossing physical barriers
 Immune cell-mediated killing
 Alteration of apoptosis pathway

MECHANISMS OF VIRAL INJURY:
CONT…..
Induction of cell proliferation and transformation
 Inhibition of host cell DNA,RNA or protein
synthesis
 Damage to plasma membrane
 Damage to cells involved in antimicrobial defense

MECHANISMS OF BACTERIAL INJURY:
Depends upon their ability to
Adhere to host cells
(b)
Invade the cells and tissues
(c)
To deliver toxins that damage the cells and
toxins

Bacterial adherence to host cells
Mechanisms- Adhesins, fibrils and fimbrae
(a)
VIRULENCE OF INTRACELLULAR
BACTERIA:
Facultative intracellular bacteria
 Subversion of host immune response
 Inhibition of synthesis of host cell proteins

ELABORATION OF BACTERIAL
ENDOTOXINS:
Septic shock
 Disseminated intravascular coagulation
 cytokines

BACTERIAL ENDOTOXINS
Bacterial enzymes
 Inhibition of protein synthesis
 Cellular necrosis
 Neurotoxins- Cl.Botulinum and Cl.Tatani,
paralysis, respiratory failure

WHAT IS PATHOLOGY?

Study of derangement of molecules, cells, tissues,
and function in the living organisms in response
to injurious agents and deprivations
COMMON TERMS USED IN
PATHOLOGY
Lesions (Gross, microscopic, chemical, molecular,
immunologic)
 Etiology
 Pathogenesis
 Symptoms
 Postmortem examination/autopsy/necropsy
 Biopsy
 Morbid changes
 Postmortem changes

HISTORY
The first concept of disease  The demoniac concept of
disease- witch doctor (17 thousand years old-Paintings
in the caves of Pyrenees mountains)
 Theological concept of disease 4000 B.C.
(embalming)- disease due to divine displeasure- Priest
 Humoral concept of disease- Greece-Hippocrates
(460-377 B.C.)




Blood-warm and moist (air)
Phlegm- cold and moist (water)
Yellow bile- warm and dry (fire)
Black bile- cold and dry (earth)
DEVELOPMENT OF ANATOMY, PHYSIOLOGY,
AND PATHOLOGY


Aristotle (384-322 B.C.) - modern anatomy and
physiology
Claudius Galen (131-206 A.D.)- Father of
anatomy
FIRST TEXTBOOK ON
VETERINARY MEDICINE

Renatus Vegetius (450-500 A.D.) “Book of the
Veterinary Art” – father of veterinary medicine
CENTURY OF ANATOMY
Antanio
Benivieni (1440-1502)postmortem examination- father of
Pathological anatomy
Leonardo da Vinci (1452-1519)Artist- Anatomy of horse
Andreas Vesaleus (1514-1564)Belgian- At the age of 24 became
Professor of anatomy at Padua, in
Italy
DISCOVERY OF BLOOD CIRCULATION
William Harvey (1578-1657)- Englishmanairtree
 Marcello Malpighi (1628-1694)- Italiancapillaries and erythrocytes, and microscopic
description of kidney, lungs, and spleen

INVENTION OF MICROSCOPE

Antony van Leeuwenhoek (1632-1723)- Dutch
draper- made 200 microscopes
FIRST TEXT BOOK OF PATHOLOGY
Jean
Fernet (1497-1558)Frenchman
Giovanni Battista Morgagni
(1682-1771)-modern
Pathology- Seats and causes
of disease in 5 volumescorrelation of lesions with
the symptoms
FATHER OF HISTOLOGY

Marei-Farancois Xavier Bichat (1771-1802)Frenchman – body composed of 21 tissues
FATHER OF IMMUNOLOGY
Edward Jenner (1749-1823)- Englishmandiscovered vaccination
 Material from cowpox lesions could be used to
protect small pox in humans

ESTABLISHMENT OF FIRST
VETERINARY SCHOOL
Jacques
Labessie De
Solleysel (1617-1680) –
Complete book on veterinary
medicine
Claude Bourgelat (17121779) – lawyer – book on
equine medicine
January 1, 1762 in Lyon,
FIRST EXPERIMENTAL PATHOLOGIST
John
Hunter (1728-1793) –
Scotch- Blood, inflammation,
gunshot wounds, monograph
“Venereal Disease”- Syphilis
Treponema pallidum
Julius
Cohnheim (1839-1884)
– German - Inflammation
CELLULAR PATHOLOGY
Johannes
Mueller (1801-1858)German- used microscope to study
tissues
Rudolph Virchow (1821-1902)- Book
“Cellular Pathology” . Father of
Cellular Pathology or Father of
Modern Pathology.
Most of the terms used in pathology
are coined by him
GERM THEORY OF DISEASE
Louis Pasteur (1822-1895) – France – germ
theory of disease
 Robert Koch (1843-1910)
DISCOVERY OF PHAGOCYTOSIS

Elie Metchnikoff (1845-1916) - Russian
DISCOVERY OF LYSOSOMES
Christian de Duve (1955) in Belgium- fractional
centrifugation
 Novikoff
 Confirmed presence of lysosomes by EM.

DISCOVERY OF PRIONS
Proteinaceous
infective particle
(Prion)
Lack nucleic acid(RNA, DNA)
No inflammatory or immune
reponse
Resistant to UV light &
disinfectants
Cause tranmissible spongiform
encephalopathies (TSE’s)