Session 1 Basic concepts of Pathology

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Lecture Notes

Session 1: Basic concepts of Pathology

Felician Sikujua (MD)

Learning tasks

At the end of this session, students are expected to be able to:

Define pathology.

Explain evolution of pathology.

Identify subdivisions of pathology.

Explain disease development.

Classify categories of diseases.

Activity: Brainstorming

What is Pathology?

Definition of Pathology

Originated from two Greek words: pathos (suffering) and logos (study of).

Pathology is the scientific study of disease.

Describes causes and effects of disease, and the functional and structural changes that occur.

Explains how these changes correlate with clinical manifestations of the disease.

Pathology gives the assist in the accurate diagnosis and treatment of diseases.

Evolution of Pathology

Evolution of Pathology described with the following concepts from different era

Religious and superstitious beliefs to rational approach (Antiquity to AD 1500).

Era of gross pathology (AD 1500 to 1800).

Era of technology development and cellular pathology (AD 1800 to 1950s).

Era of modern pathology (1960s to dawn of 21st century).

Evolution of Pathology cont…

Religious and superstitious beliefs to rational approach (Antiquity to AD 1500).

Disease was the outcome of curse or evil eye of spirits.

Era of gross pathology (AD 1500 to 1800).

Dissection of human body & autopsy.

Discovery of first ever microscope.

Evolution of Pathology cont…

Era of technology development and cellular pathology (AD 1800 to 1950s).

Advanced microscopy technology.

Staining techniques were introduced.

Papanicolaou in 1930s developed the use of exfoliative cytology for early detection of cervical cancer.

Evolution of Pathology cont…

Era of modern pathology (1960s to dawn of 21st century).

Major advances in molecular biology.

Some of discoveries on molecular biology are

Description of the structure of DNA of the cell.

Identification of chromosomes and their correct number.

Recombinant DNA technique developed.

Introduction of polymerase chain reaction (PCR).

Mammalian cloning.

Era of stem cell research.

Subdivision of Pathology

Traditionally, Pathology is divided into two subdivisions

General pathology.

It focuses on common cellular and tissue alterations caused by pathologic stimuli in most tissues. e.g. Inflammation, cancer, aging.

Systemic pathology.

It examines the reactions and abnormalities of different specialized organs. e.g. Goiter (thyroid), pneumonia (lung), cirrhosis (liver).

Subspecialties of Pathology

With the advancement of diagnostic tools, the speciality of pathology has come to include some of the following subspecialities:

Histopathology.

Haematology.

Chemical pathology.

Immunopathology.

Medical genetics.

Molecular pathology.

Histopathology

It is also known as anatomic pathology, pathologic anatomy or morbid anatomy.

It is the classic method of studying different pathologies.

Most useful subspecialty which has stood the test of time.

The study includes structural changes observed by naked eye and microscopy supported by numerous special staining methods.

Subdivisions of Histopathology

Surgical pathology.

Study of tissues removed from the living body.

Forensic pathology and autopsy work.

Study of organs and tissues removed at postmortem for medicolegal work and or for determining sequence and cause of death.

Cytopathology.

Study of cells shed off from lesions and from superficial and deep-seated lesions for diagnosis.

Disease development

Disease is defined as an abnormal variation in structure or function of any part of the body.

There are four (4) core aspects for disease development

Aetiology.

Pathogenesis.

Morphologic changes.

Functional derangements and clinical significance.

Aetiology

Aetiology is the origin of a disease, including the underlying causes and modifying factors.

Aetiology forms the core of the Pathology.

It refers to why a disease arises.

Knowledge or discovery of the primary cause remains the backbone on which diagnosis can be made, disease is understood or treatment is developed.

Aetiology

There are two major classes of aetiologic factors

Genetic (Intrinsic) factor.

Acquired (Environmental) factor.

There is an interaction of these aetiologic factors in disease causation.

Understanding the genetic and environmental factors underlying diseases is a major theme of modern medicine.

Aetiology:Genetic factors

These are the results of activities of single genes and groups of genes.

Both normal and abnormal gene influence susceptibility and resistance to disease.

Examples of diseases and their genetic predisposing factor from normal genes.

Susceptibility of fair (light) skin to damage e.g. skin cancer by the ultraviolet rays in sunlight.

Blood group B is associated with duodenal ulcer.

The blood group Duffy negative confers resistance to infection by Plasmodium vivax.

Aetiology:Genetic factors cont…

Abnormal genes

Mutations give rise to abnormalities of chromosomes and components genes.

Mutations occur spontaneously without known cause.

In some cases mutations are caused by radiations, chemicals or infective agents.

Aetiology:Genetic factors cont…

There are hereditary diseases where genetic abnormality directly determines a disease. e.g. Albinism.

But most of genetic diseases are multifactorial (genetic and environmental factors). e.g. Diabetes.

There is acquired specific genetic abnormality in stem cells, which potentiate the development of malignant tumours.

Aetiology: Environmental factors

These include

Physical agents.

Chemical agents.

Infections/infestations (Biological agents).

Nutritional imbalances.

Abnormal immunological reactions.

Psychological factors.

Aetiology: Environmental factors cont…

Physical agents

Physical agents include

Trauma.

Radiations.

Extreme heat and cold.

Electrical power.

Changes in atmospheric pressure.

Aetiology: Environmental factors cont…

Chemical agents

These are increasing with the advances in industrial processing, some act in general manner i.e. the toxic effect is to all cells.

Some act locally example acids and caustics on the skin and mucous membrane.

Some affect certain organs such as lungs, kidneys, liver and pancreas.

Aetiology: Environmental factors cont…

Infections/infestations (Biological agents).

Bacteria.

Viruses.

Fungi.

Parasites.

They cause diseases by direct destruction to the tissue or due to toxins produced by these agents.

Aetiology: Environmental factors cont…

Nutritional imbalance (Nutritional deficiency or excess).

Nutritional deficiency result from poor supply, interference with absorption, inefficient transport within the body or defective utilisation of nutrients.

Dietary excess can the cause of many systemic diseases such as cardiac diseases.

Aetiology: Environmental factors cont…

Abnormal immunological reactions (Immunological factors)

The immune process is normally protective but in certain circumstances the reaction may become deranged.

Hypersensitivity to various substances can lead to alarming shock-like conditions- anaphylaxis.

Immune process may act against the body cells– autoimmunity.

Aetiology: Environmental factors cont…

Psychological factors

They 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.

Pathogenesis

Mechanism on how etiologic factors trigger cellular and molecular changes that give rise to the specific functional and structural abnormalities that characterize the disease.

Pathogenesis describes how a disease develops.

The study of pathogenesis remains the main domain of pathology.

Pathogenesis leads to morphologic changes.

Morphologic changes

Structural alterations in cells or tissue that are either characteristic of the disease or diagnostic of the aetiologic process.

They occur following the pathogenetic mechanisms.

The structural changes in the organ can be seen by naked eye or under the microscope.

Morphologic changes cont…

Structural changes seen by naked eye are called gross morphologic changes (macroscopic changes).

Look for size, shape, consistency, colour of the affected tissue/organ.

Structural changes seen under the microscope are called microscopic changes (histological changes).

Morphologic changes will lead to functional alteration and to the clinical signs & symptoms of the disease.

Functional derangements and Clinical significance

The functional consequences of the morphologic changes.

Morphologic changes will determine

Clinical features (symptoms and signs).

Course of the disease.

Prognosis of the disease.

Classification of diseases

Basing on body response disease can be classified as

Congenital diseases.

Inflammatory diseases.

Degenerative diseases.

Neoplastic diseases.

Key points

Pathology is the scientific study of disease.

It is broadly subdivided into General Pathology and Systemic Pathology.

Pathology has been evolved over the centuries from supernatural beliefs to the present state of knowledge of modern pathology.

Pathology provides the scientific foundation for the practice of medicine.

Pathology gives explanations of a disease by studying the four core aspects of the disease.

Review questions

Define Pathology

What are the era involved in evolution of Pathology?

Outline three (3) subdivisions of histopathology

Explain factors contribute to disease development?

How can diseases be classified basing on body responses?

References

Bezabeh M.; Tesfaye A.; Ergicho B. et al (2004): General pathology lecture notes for Health Sciences students. Ethiopia Public Health Training Initiative. Pg. 1-2.

Kumar V. ; Abbas A. K. ; Aster J. C.;(2013): Robbins and Contran Pathologic Basis of Disease (9th Ed.) Elsevier Saunders, USA. Pg. 1.

Mohan H.;(2010): Text book of Pathology (6th Ed.) Jaypee Brothers Medical Publishers, India. Pg. 1-7.

Sanchez A.; Barone J.;(2013): USMLE Step 1 Pathology lecture notes. Kaplan Inc, USA. Pg. 1.

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Session 1 Basic concepts of Pathology

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