INTRODUCTION: On exposure to stress, the cells make adjustments with the changes in their environment to: * Physiologic needs *Pathologic injury
ADAPTATION: PHYSIOLOGIC: Represents cells to normal stimulation by hormones/ endogenous chemical substances. PATHOLOGIC: The cells have the ability to modulate their environment.
SURVIVAL OF THE FITTEST: Adaptive responses are reversible on withdrawal of stimulus. If the irritant / stimulus persists for a longer time cell may not be able to survive. Thus, the concept of evolution “ survival of fittest” holds true for adaptation as “survival of adaptable”.
MECHANISM: Altered cell surface receptor binding. Alterations in signal for protein synthesis. Synthesis of new proteins by the target cell such as heat-shock proteins.
HYPERTROPHY: An increase in the size of the cells, which results in enlargement of organ without any changes in the number of cells. Occurs due to incresed functional demand & hormonal stimulation.
HYPERPLASIA: An increase in number of parenchymal cells, which results in enlargement of organ/tissue.
CAUSES: PHYSIOLOGIC: HORMONAL: Eg: Hyperplasia of pregnant uterus COMPENSATORY: Eg: Regeneratio of liver.
CAUSES: PATHOLOGIC: Occurs due to excessive stimulation of hormones & growth factors. Eg: Endometrial hyperplasia-following oestrogen excess.
METAPLASIA: META-Transformation PLASIA-Growth It is a reversible change of one type of epithelial or mesenchymal cells, usually in response to persistant abnormal stimulus which in turn may change into a malignant cell.
EPITHELIAL METAPLASIA: The most common type. Metaplastic change cane either patchy or diffuse. Leads to alterations in the epithelium. Deprivation of protective mucous secretion. More prone to infection.
TYPES: SQAMOUS METAPLASIA: Occurs due to chronic irritation (chemical/mechanical/infective) Eg: Bronchus in chronic smokers. COLUMNAR METAPLASIA: Eg: Intestinal metaplasia in healed chronic gastric ulcer.
MESENCHYMALMETAPLASIA: Less often there is transformation of one type of mesenchymal tissue to another. OSSEOUS: Formation of bone in fibrous tissue, cartilage & myxoid tissue. Eg: In arterial wall in old people. CARTILAGENOUS: In healing of fractures, where there is undue mobility.
DYSPLASIA: Disordered cellular development often accompanied with metaplasia & hyperplasia (ATYPICAL HYPERPLASIA). Occurs most often in epithelial cells, which is characterised by cellular proliferation & cytologic changes.
CAUSES: Occurs due to chronic irritation or prolonged inflammation. On removal of simulus, the changes may disappear. In majority of cases dysplasia progresses into carcinoma insitu or invasive cancer.
CHANGES: Increased number of layers of epithelial cells. Disorderly arranged cells. Loss of basal polarity. Cellular & nuclear pleomorphism. Increased nucleocytoplasmic ratio. Nuclear hyperchromatism. Increased mitotic activity.