66. The following are example of Apootosis Except- a) Graft versus host disease b) Menstrual cycle c) Pathological atrophy following duct obstruction d) Tumour necrosis Ans: d) -------------- Apoptosis: Programmed cell death is called apoptosis. Programmed cell death is needed to destroy cells that represent a threat to the integrity of the organism. Examples: Cells infected with viruses: One of the methods by which cytotoxic T lymphocytes (CTLs) kill virus-infected cells is by inducing apoptosis. -- Cells of the immune system: As cell-mediated immune responses wane, the effector cells must be removed to prevent them from attacking body constituents. CTLs induce apoptosis in each other and even in themselves. Defects in the apoptotic machinery is associated with autoimmune diseases such as lupus erythematosus and rheumatoid arthritis. Cells with DNA damage: Damage to its genome can cause a cell â€¢to disrupt proper embryonic development leading to birth defects â€¢to become cancerous. Cells respond to DNA damage by increasing their production of p53. p53 is a potent inducer of apoptosis. Cancer cells: Radiation and chemicals used in cancer therapy induce apoptosis in some types of cancer cells. Menstruation refers to the monthly shedding of the lining of the uterus (the womb), released through the vagina. The menstrual cycle begins the first day a woman bleeds â€“ in other words, the first day of a period. Apoptosis is the death of single cells within clusters of other cells. Apoptosis seen in: ----> I. Physiological conditions like: a. Endometrial cell death during Menstuation cycle b. Cell death os virus infected or neoplastic cells in a tumor ( T-cell induced) c. Removal of cells during embryogenesis, II. Pathological conditions like: a. Graft - versus host diseases b. Atropy of glands following duct obliteration.