PATHOLOGY COURSE CODE : PHR 214 COURSE TEACHER : ZARA SHEIKH

Pathology is the study of disease. Patho is a Greek word meaning suffering. Logo means study. This branch of science is concerned with the structural and functional changes in cells, tissues and organs that underlie the disease. By the use of molecular, microbiologic, immunologic and morphologic techniques, pathology attempts to explain the cause of the signs and symptoms of the disease and thus provides a foundation for rational care and therapy.

The study of Pathology is divided into two broad categories : General PathologySystemic Pathology

General Pathology is concerned with the basic reactions of cells and tissues to abnormal stimuli underlying the disease. Systemic Pathology examines the specific responses of specialized organs and tissues to more or less well defined stimuli. Four aspects of a disease are 1.Etiology (cause) 2.Pathogenesis(mechanism of its development) 3.Morphologic changes (structural alterations induced in the cells and organs of the body) 4.Clinical Expression (signs and symptoms)

CELLULAR RESPONSES TO STRESS AND NOXIOUS STIMULI As cells encounter physiologic stresses or pathologic stimuli, they can undergo adaptation, achieving a new steady state and preserving viability and function. Principal adaptive responses are -hypertrophy, -hyperplasia, -atrophy, and -metaplasia.

NORMAL CELL (HOMEOSTASIS) STRESS, INCREASED DEMAND ADAPTATION INJURIOUS STIMULUS CELL INJURY CELL DEATH Inability to adapt

CELLULAR ADAPTATIONS Hyperplasia Hypertrophy Atrophy Metaplasia Inability to adapt results in cell injury and may lead to cell death.

Hyperplasia – Increase in the number of cells as a result of cell division. Hypertrophy – Increase in the sizes of the individual cells. Atrophy – Decrease in the size and function of cells. Cell Injury – If the limits of the adaptive response is exceeded or when the cell is exposed to an injurious agent or stress, a sequence of events follow which is termed as cell injury.

Cell injury is reversible up to a certain point, but if the stimulus persists or is severe then the cell reaches the ‘point of no return’ and suffers irreversible cell injury and ultimately cell death. For example, in response to increased haemodynamic loads, the heart muscle first becomes enlarged which is a form of adaptation. If the blood supply to the myocardium is insufficient to cope with the demand, the muscle becomes reversibly injured and finally undergoes cell death.

Cell Death Causes of cell death : Ischemia (lack of blood flow) Infections Toxins Immune reactions Cell Death is a normal and essential part of embryogenesis, the development of organs, the maintenance of homeostasis and the aim of cancer therapy.

Cell Death There are two principal patterns of death. - APOPTOSIS - NECROSIS Necrosis is the type of cell death that occurs after such abnormal stresses such as ischemia and chemical injury and it is always pathologic. Apoptosis occurs when a cell dies through activation of an internally controlled suicide program. It is designed to eliminate unwanted cells during embryogenesis and in various physiologic processes such as involution of hormone responsive tissues upon withdrawal of the hormone.

References Robbins and Cotran Pathologic Basis of Disease. Chapter-1. Eight Edition. Edited by Kumar, Abbas, Fausto.