Cell Death

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Cell Death

• Hoon Lee

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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)

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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.

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Cytological characteristics of Necrosis

• Initial swelling of the cell.
• Rupture of the plasma membrane.
• Cytoplasm is spilled to the extracellular
  environment.

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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)

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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

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Cytological characteristics of Apoptosis

• Nucleus condensation.
• Membranes preserved.
• Fragmentation.
• phagocytosis

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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.

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Mechanism of Apoptosis

• Internal signals Mitochondrial pathway.
• External signals Death receptor pathway.
• Apoptosis-Inducing Factor.

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Internal signals Mitochondrial pathway
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External signals Death receptor pathway
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Apoptosis-Inducing Factor (AIF)

• Release from the mitochondria.
• Migrates into the nucleus.
• Bind to DNA.
• Destruction of the DNA
• Cell death.