Cell Injury, Death And Adaptation

Cell Injury, death and adaptation Causes of Cell Injury: • • • • •

Hypoxia Physical agents (heat, cold, radiation, trauma) Chemical agents and drugs Microbiologic agents Immunologic reactions

• Genetic defects • Nutritional imbalances Principles of Cell Injury: • Dependent upon: - the etiology - duration - severity of the inciting injury - cell type - stage of cell cycle - cell adaptability •

Cellular membranes, mitochondria, endoplasmic reticulum and the genetic apparatus are particularly vulnerable • Injury at one focus often has a cascade effect • Morphologic reactions occur only after critical biochemical (molecular) damage .

Normal Cell [ homeostasis]

Stress. increased demand

Injurious stimulus

Adaptation Done By: Bas Dh. © class of 205

Cell injury Cell death Inability to adapt 1

2006-2007

Atrophy: Acquired shrinkage in the size of the cell. - physiologic :  Fetus - branchial clefts - thyroglossal dust  Neonate - ductus arteriosus - umbilical vessel  Post adolescence - lymphoid tissue: tonsils, thymus , appendix  adult - post-menopausal atrophy of the uterus, ovaries and breast. - Pathologic  localized - ischemia : e.g. cerebral atrophy due to arthrosclerosis - pressure : e.g. hydronephrosis - disuse : e.g. immobilization, obstruction of a duct draining an exocrine gland - loss of innervation : e.g. nerve damage result in atrophy of the muscles they supply - hormonal stimulation : e.g. decreased estrogen after menopause result in atrophy of the endometrium, vaginal epithelium and breast; testicular atrophy in cirrhosis, estrogen therapy etc.  generalized - starvation , malnutrition - senility - hypopituitarism Hypertrophy : •

An increase in the size of the cells and thus an increase in the size of the tissue or organ [ thus, hypertrophy is seen often in those tissues that are unable to divide: their only effective response is to enlarge] • The end result is to lessen the amount of increased work that each individual cell must perform in response to the stimulation or stress • In a pure form, it is found only in muscle and is usually a response to : - increased demand for work - increased stimulation by growth hormone e.g. tongue and heart acromegaly

Done By: Bas Dh. © class of 205

2

2006-2007

Hyperplasia : • An increase in the number of cells in an organ or tissue [ thus, this response is seen only in those tissues in which cell division can still occur] • May or may not be seen in conjunction with hypertrophy • Endocrine glands e.g.: - adrenal cortex due to increased ACTH - parathyroid: primary or secondary to chronic renal failure • Endocrine target organs e.g. - breast either physiologic or pathologic - endometrium - prostate • Skin and lining epithelia : e.g. in chronic dermatitis; warts ; margins of healing ulcer • Bone marrow where there is increased demand for RBC’s

Done By: Bas Dh. © class of 205

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2006-2007