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.
Apoptosis-Inducing Factor (AIF) • Release from the mitochondria. • Migrates into the nucleus. • Bind to DNA. • Destruction of the DNA • Cell death.