Histology Wk 9

Question 1

LOOK AT MITOSIS NOTES FROM PPT ON GOODNOTES

Question 2

NECROSIS VS APOPTOSIS

Answer 2

LOOK AT GOODNOTES

Question 3

Apoptosis

Answer 3

Apoptosis is a rapid, highly regulated cellular activity that shrinks and eliminates defective and unneeded cells . It results in small membrane-enclosed apoptotic bodies, which quickly undergo phagocytosis by neighboring cells or cells specialized for debris removal. Apoptotic cells do not rupture and release none of their contents, unlike cells that die as a result of injury and undergo necrosis.

Question 4

Apoptosis

Answer 4

Apoptosis is controlled by cytoplasmic proteins in the Bcl-2 family, which regulate the release of death-promoting factors from mitochondria. Activated by either external signals or irreversible internal damage, specific Bcl-2 proteins induce a process with the following features:
■■ Loss of mitochondrial function and caspase activation: Bcl-2 proteins associated with the outer mitochondrial membrane compromise membrane integrity, stopping normal activity and releasing cytochrome c into the cytoplasm where it activates proteolytic enzymes called caspases. The initial caspases activate a cascade of other caspases, resulting in protein degradation throughout the cell.
■■ Fragmentation of DNA: Endonucleases are activated, which cleave DNA between nucleosomes into small fragments. (The new ends produced in the fragmented DNA allow apoptotic cells to be stained histochemically using an appropriate enzyme that adds labeled nucleotides at these sites.)
■■ Shrinkage of nuclear and cell volumes: Destruction of the cytoskeleton and chromatin causes the cell to shrink quickly, producing small structures with dense, darkly stained pyknotic nuclei that may be identifiable with the light microscope.
■■ Cell membrane changes: The plasma membrane of the shrinking cell undergoes dramatic shape changes, such as “blebbing,” as membrane proteins are degraded and lipid mobility increases.
■■ Formation and phagocytic removal: Membrane-bound remnants of cytoplasm and nucleus separate as very small apoptotic bodies. Newly exposed phospholipids on these bodies induce their phagocytosis by neighboring cells or white blood cells.

Question 5

Necrosis

Answer 5

Necrosis, or accidental cell death, is a pathologic process. It occurs when cells are exposed to an unfavorable physical or chemical environment (e.g., hypothermia, hypoxia, radiation, low pH, cell trauma) that causes acute cellular injury and damage to the plasma membrane. Under physiologic conditions, damage to the plasma membrane may also be initiated by viruses, or proteins called perforins. Rapid cell swelling and lysis are two characteristic features of this process.