1- Introduction of Pathology

Objectives of the lecture To learn some terms used in pathology To learn about cell injury To know about cell adaptation To know about causes of cell atrophy

Pathology is "Scientific study of disease “ Study of structural and functional changes in disease. You need to have a basic knowledge of normal Anatomy (structure) and Physiology (function) to understand Pathology.

Diseases is an expression of "discomfort" due to structural or functional abnormality. This abnormality can be caused by various agents Eg. Bacteria, virus, heat, radiation etc. collectively called 'etiology'.

Factors causing disease are mainly two types Factors causing disease are mainly two types. Environmental (or external) factors and Genetic (or Internal) factors. Diseases which present since birth are called Congenital diseases and all other diseases are known as Acquired diseases. Diseases which occur in families are known as Familial diseases.

Pathology of a disease is formally studied under four subdivisions Pathology of a disease is formally studied under four subdivisions. - Etiology - Study of cause / causative agent of disease - Pathogenesis- Study of disease progression or evolution. - Morphology - Study of structural changes in disease (Gross & microscopic) - Clinical Significance - Study of how clinical features are related to changes.

Major groups of diseases are Inflammatory, Degenerative & Neoplastic Major groups of diseases are Inflammatory, Degenerative & Neoplastic. Inflammatory disorders are due to damage to tissues by various injuries (physical, chemical, infections etc.) Degenerative disorders are due to lack of growth or ageing. Neoplastic disorders are due to excess cell division forming tumours.

Cell & Tissue Injury

Cell Injury Damage or alteration of one or more cellular components Many types of injury are tissue-specific because of anatomic relationships and tissue response to chemical and infectious agents. Cell injury disrupt cell physiology; so the cell does not function at full capacity.

Stages in the cellular response to stress and injurious stimuli

Cell Injury Produces: Signs: abnormal physical findings – Objective. Symptoms : complaints experienced by the patient – Subjective.

Causes of Cell and Tissue Injury Physical agents Chemicals and drugs Infectious pathogens Immunologic reactions Genetic mutations Nutritional imbalances

A. Inadequate blood supply B. Lung disease C. Heart failure D. Shock Hypoxia and Ischemia: cell injury resulting from inadequate levels of oxygen. Causes: A. Inadequate blood supply B. Lung disease C. Heart failure D. Shock

hypoxia and ischemia- why so important? All cells in the body require a continuous supply of oxygen in order to produce ATP via oxidative phosphorylation in mitochondria. ATP is absolutely critical for life.

Susceptibility of specific cells to ischemic injury Neurons: 3 to 5 min. Myocytes, hepatocytes, renal epithelium: 30 min. to 2 hr. Cells of soft tissue, skin, skeletal muscle: many hours

Outcomes from cell injury depend upon: Type of injury Severity of the injury Duration of the injury Type of cell being injured- Some cell types sustain injury better than others; some tissues (e.g. liver) have a capacity to regenerate.

Vulnerable Sites of the Cell Cell membranes Mitochondria Endoplasmic reticulum Nucleus

Consequences of Injury (Reversible): No long term effects- the cell damage is repaired, the effects of the injury are reversible. The cell “adapts” to the mild damaging stimulus. (Irreversible): The cell dies, undergoing necrosis. The damage is irreversible.

Adaptation to injury 1. Atrophy: decrease in the size and functional capacity of the cell, after normal growth has been attained . ( O2, blood, nerve supply) 2. Hypertrophy: an increase in the size of the cell secondary to an increase in cell function. Increase in the number of mitochondria and ER, etc.

Causes of Cell Atrophy Loss of blood supply or innervations Loss of Hormones (eg. TSH) Decrease in the workload Aging, chronic illness

3. Hyperplasia: an increase in the number of cells of a tissue in response to a stimulus or injury. 4. Metaplasia: replacement of one type of tissue with another in response to an injury.

5. Hypoplasia: incomplete development or underdevelopment of an organ / tissue (less severe in degree than aplasia). 6. Aplasia: lack of development of an organ or tissue (may have a rudimentary organ). can also refer to lack of production of cells from an organ or tissue (e.g. aplastic anemia).

Hypertrophy versus Necrosis

Muscular hypertrophy Metaplasia 2.5