Cell Death Hoon Lee Cell Death Within each cell line, the control of cell number is regulated by a balance of cell proliferation and cell death. There are two principle patterns of cell death 1. Necrosis (death by injury) 2. Apoptosis (death by suicide) Necrosis Refer to cell death in an organ or tissue. Caused by infarction, infectious disease, poisoning etc. Affects contiguous groups of cell. Usually precipitates an inflammatory response. Cytological characteristics of Necrosis Initial swelling of the cell. Rupture of the plasma membrane. Cytoplasm is spilled to the extracellular environment. Types of Necrosis Coagulation Necrosis (seen in infarcted organs, e.g.myocardial infarct). Liquefaction Necrosis (softening of the center of an abscess) Caseous Necrosis (cheesy, crumbly appearance, e.g. Tuberculosis lesion in the lung) Apoptosis Responsible for Programmed Cell Death (PCD) Plays an important role in multicellular development. Cause deletion of individual cells in the midst of others. No inflammatory response but rapid phagocytosis Cytological characteristics of Apoptosis Nucleus condensation. Membranes preserved. Fragmentation. phagocytosis Examples of Programmed Cell Death Phylogenic: the loss of the vertebrate tail during human fetal development. Morphogenic: the loss of mesenchyme between the digit. Histogenic: the reduction of numbers of neurons in the developing brain. *(PCD occurs during embryonic development as mitosis) Normal maintenance. Suicide cell death: virtually infected cells. Mechanism of Apoptosis Internal signals: Mitochondrial pathway. External signals: Death receptor pathway. Apoptosis-Inducing Factor. Internal signals: Mitochondrial pathway External signals: Death receptor pathway Apoptosis-Inducing Factor (AIF) Release from the mitochondria. Migrates into the nucleus. Bind to DNA. Destruction of the DNA Cell death.