2. Apoptosis
Apoptosis = falling off or dropping off, as that of leaves or petals.
Def:
Programmed and coordinated cell death.
Apoptosis is a pathway of cell death in which cells activate enzymes that
degrade the cells’ own nuclear DNA and nuclear and cytoplasmic
proteins.
3.
4. Features of Apoptosis
Cell size: Reduced (shrinkage).
Nucleus: Fragmentation into nucleosome-sized fragment.
Plasma membrane: Intact; altered structure especially orientation of lipids.
Cellular contents: Intact; may be released in apoptotic bodies.
Adjacent inflammation: No.
Physiologic role: Often physiologic means of eliminating unwanted cells.
pathologic role: pathologic after some forms of cell injury, especially DNA and protein
damage.
6. Causes of Apoptosis
A.Physiologic apoptosis:
During normal development of an organism, some cells die and are replaced by
new ones.
In mature organisms, highly proliferative and hormone- responsive tissues
undergo cycles of proliferation and cell loss that are often determined by the levels
of growth factors.
In these situations, the cell death is always by apoptosis, ensuring that unwanted
cells are eliminated without eliciting potentially harmful inflammation.
In the immune system, apoptosis eliminates excess leukocytes left at the end of
immune responses as well as lymphocytes that recognize self-antigens and could
cause autoimmune diseases if they were not purged.
7. B. Pathological apoptosis
Apoptosis eliminates cells that are damaged beyond repair.
This is seen when there is severe DNA damage, for example, after exposure to
radiation and cytotoxic drugs.
The accumulation of misfolded proteins also triggers apoptotic death.
Certain infectious agents, particularly some viruses, induce apoptotic death of
infected cells
8. Mechanisms of Apoptosis
Apoptosis is regulated by biochemical pathways that control the balance of death
and survival inducing signals and ultimately the activation of enzymes called
caspases.
Caspases were so named because they are cysteine proteases that cleave proteins
after aspartic acid residues.
Activated caspases lead to activation of nucleases that degrade DNA& others
enzymes that destroy nucleoproteins & cytoskeletal proteins.
9. Mechanisms of Apoptosis
1. Intrinsic ( mitochondrial) pathway.
2. Extrinsic ( death receptor ) pathway.
- Clearance of apoptotic cells.
12. Gross
The fragments are quickly extruded and phagocyte
without eliciting an
inflammatory response, even substantial apoptosis may be
histologically undetectable
