34. Necrosis: stages of morphogenesis, clinical and morphological criteria of cell death, pathoanatomical types. Macro-, microscopic signs of necrosis, outcomes.

Anatomical signs: violation of the anatomical pattern, discoloration, consistency.

Ultrastructural signs of necrosis. Reflect changes in cell organelles:

• in the nucleus: chromatin aggregation, fibrillation fragmentation, complete destruction;

• in the mitochondria: swelling, decrease in the density of matrix granules, formation of irregularly shaped aggregates in it, deposition of calcium salts;

• in the cytoplasmic reticulum: swelling, fragmentation and disintegration of membrane structures;

• in polysomes and ribosomes: the breakdown of polysomes, the separation of ribosomes from the surface of tanks, a decrease in the clarity of contours and sizes, as well as the number of ribosomes;

• in lysosomes: aggregation of small dense granules of marix and its enlightenment,

• rupture of membranes; and in the cytoplasmic matrix: disappearance of glycogen granules, decrease in enzyme activity

Microscopic signs of necrosis:

a) in the nucleus: karyopycnosis (wrinkling and condensation of chromatin), karyorexis (disintegration into lumps), karyolysis (dissolution)

b) in the cytoplasm: denaturation and coagulation of proteins (focal or complete) → plasmorexis (disintegration of the cytoplasm into lumps) → plasmolysis (hydration and hydrolytic melting of cytoplasm

c) intermediate substance: depolymerization of glycosaminoglycans, impregnation with plasma proteins, swelling, melting

d) collagen fibers swell, impregnated with fibrin → dense homogeneous masses → disintegration; elastic fibers: swelling, basophilia, disintegration, melting (elastolysis); fragmentation and lumpy disintegration of reticular and nerve fibers

e) when cells and intercellular matter disintegrate, tissue detritus is formed, with demarcation inflammation around it.

Macroscopic signs of necrosis:

a) necrotic tissue is dense and dry (mummification) or flabby, molten (myomalacia, encephalomalacia)

b) pale, white-yellow tissue (foci of necrosis in the kidneys, spleen, myocardium); dark red, soaked in blood (foci of circulatory necrosis in the lungs); stained with secretions (foci of intestinal necrosis, etc.)

c) in case of putrefactive decay: a bad smell.

Necrosis outcomes:

a) demarcation inflammation and demarcation zone limiting necrosis → melting of necrotic masses and replacement with connective tissue (organization) → scar → encapsulation of the necrosis focus, calcification (petrification), ossification

b) resorption of tissue detritus and capsule formation → cavity at the site of necrosis (cyst)

c) purulent melting of the necrosis focus (septic infarcts)

The meaning of necrosis:

1) necrosis of vital organs → death (MI, ischemic necrosis g/m, acute pancreatic necrosis, necrosis of the cortical substance of the kidneys)

2) necrosis as a cause of complication (infections with massive bedsores)

3) necrosis as a cause of intoxication (with gangrene of the limb)

4) necrosis as a cause of sepsis