Page 49 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

The cell (cellula) 31

degenerative disease). There are two mechanisms of cell by the cell itself. The stages in apoptosis are shown in
VetBooks.ir death: Figure 1.41:

· necrosis (accidental cell death [pathological]) and
· apoptosis (programmed cell death). · a reduction in cell volume due to shrinking of the
cytoplasm and arrangement of the cytoskeleton into
concentric bundles; loss of mitochondrial function
Necrosis (Figure 1.40) results from irreversible exogenous with release of cytochrome c (resulting in activation
or endogenous injury caused by noxious physical or chem- of a cascade of proteolytic enzymes [caspases]),
ical factors (e.g. radiation, trauma, toxins, hypothermia, · fragmentation of nuclear DNA into oligonucleoso-
ischaemia) that cause disruption of the plasmalemma mal pieces (due to endonuclease activity within the
and swelling of the cytoplasm. Following rupture of the intact nuclear envelope),
cell membrane, organelles are broken down by lysosomal · modification of the plasmalemma through translo-
enzymes (autolysis). cation of intramembrane molecules to the external
The cell fragments enter the extracellular space, and surface (‘membrane blebbing’) and
the nuclear material condenses (pyknosis) and eventu- · cell breakdown with formation of membrane-
ally undergoes complete dissolution (karyolysis). Cellular bound apoptotic bodies containing organelles and
necrosis is often accompanied by damage to adjoining nuclear material – apoptosis is not associated with
tissue and initiation of inflammation. the induction of inflammation.
In contrast, apoptosis is a form of programmed cell
death. The processes involved in apoptosis are regulated

1.40 Necrosis (schematic). 1.41 Apoptosis (schematic).

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