Ans. is 'b' i.e., Apoptosis o Programmed cell death is apoptosis. o But remember this impoant fact that not all apoptosis are programmed cell death (read text below) Apoptosis o Apoptosis is pathway of cell death that is induced by a tightly regulated intracellular program in which cell destined to die activate enzymes that degrade the cell's own nuclear DNA, and nuclear & cytoplasmic proteins. o Apoptosis generally involves single cells in contrast to necrosis that usually involve a group of cells. o Apoptosis may be of two types ? A. Physiological (most of the time) Programmed cell death. B. Pathological Unprogrammed cell death. A.Physiological apoptosis o Death by apoptosis is a normal phenomenon that serves to eliminate cells that are no longer needed. o It is impoant in the following physiologic situation :? The programmed destruction of cells during embryogenesis, including implantation, organogenesis, and metamorphosis. Hormone dependent involution in adult, e.g., endometrial cell breakdown during menstural cycle, ovarian follicular atresia in the menopause, the regression of lactating breast after weaning, and prostatic atrophy after castration. Cell deletion in proliferating cell population in order to maintain a constant number, e.g., intestinal crypt epithelium. Death of host cells that have served their useful purpose, such as neutrophils after an acute inflammatory response, and lymphocytes at the end of an immune response. Elimination of potentially harmful self-reactive lymphocytes in thymus. Cell death induced by cytotoxic T cells to eliminate virus infected and neoplastic cells. Same mechanism occurs in graft versus host disease. B.Pathological apoptosis o Apoptosis may also be pathological. o When cells are damaged beyond repair, especially when the damage affects the cell's DNA, the irreparably damaged cells are eliminated : ? Cell death produced by injuries stimuli --> Radiation and cytotoxic anticancer drugs damage DNA, and if repair mechanisms cannot cope with the injury, the cell kills itself by apoptosis. In these situations, elimination of the cell may be a better alternative than risking mutations and translocations in the damaged DNA which may result in malignant transformation. Cell injury in ceain viral diseases, e.g., in viral hepatitis. Pathologic atrophy in parenchymal after duct obstruction, such as occurs in pancreas, parotid gland. Cell death in tumors.