Overview Programmed cell death requirements ATP functioning caspase enzymes for cellular degradation login to view 3 more bullets Two pathways intrinsic occurs in response to cell injury, loss of stimulatory growth factors, or DNA damage involved in embryogenesis mediated by changes in levels of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) factors login to view 5 more bullets extrinsic occurs in response to several external "death" signals login to view 6 more bullets Mechanism caspase cascade regulation login to view 10 more bullets caspases - inactive enzymes such as proteases and endonucleases login to view 3 more bullets membrane begins to bleb containing cellular fragments login to view 1 more bullet Key principles distinct histological changes cell shrinkage pyknosis eosinophilic cytoplasm membrane blebbing nuclear fragmentation (karyorrhexis) nuclear fading formation of apoptotic bodies lack of inflammation typically involves single or specific groups of cells leaving tissue architecture intact Examples menstrual shedding of endometrium apoptosis induced in the endometrium when estrogen and progesterone levels decrease destruction of specific cells during embyrogenesis loss of Mullerian structures in males due to Mullerian inhibititory factor virally infected cells apoptosis induced by cytotoxic T-cells embryogenesis apoptosis induced in skin between fingers