Term
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Definition
| local death of cellular tissue within a living animal. Significance depends on site, size, speed of progression and sequelae of necrosis. Rapid loss of tissues is always more significant that a gradual loss. Inflammatory and healing pathway may be more significant than the necrosis itself. |
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Term
| local reaction of the body to necrosis |
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Definition
| induces a mild inflammatory response= accumulation of leukocytes (mostly neutrophils)with a rim of hyperaemia = line of demarcation. |
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Term
| morphologic appearance of necrosis |
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Definition
1. cytoplasmic changes (swelling)
2.nuclear changes =
a.pyknosis- dark staining, shrunken
b.karyorrhexis- nuclear fragmentation
c.karyolysis-nucleus loses affinity for histological stains |
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Term
types of necrosis
*recall necrosis = local death of tissue within a living animal |
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Definition
1.coagulative- persistance of architectural detail.
-causes: anoxia, caustic chemicals
2.caseous- loss of architectural detail = creamy/grey homogenous granular mass.
- causes: bacterial infection
3. liquefactive (malacia)- disintegration of necrotic tissue into liquid. Usually seen in the CNS.
causes- pyogenic bacteria, Neutro.
4. fat (saponification)- death of fat cells.combine with Na+ or Ca+ to form soaps |
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Term
Sequelae of necrosis:
liquefaction |
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Definition
occurs when:
1. the number of cells is small
2. tissue is rich in enzymes (not denatured during necrosis)
3. tissues is moist
4. there are neutrophils (to release lytic enzymes) |
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Term
sequelae of necrosis:
liquefaction + pus formation = suppuration |
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Definition
involves pyrogenic bacteria which attract neutrophils.
pus= neutrophils and necrotic tissue suspended in tissue fluid.
pus formation within a tissue = an abcess |
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Term
sequelae of necrosis:
encapsulation with liquefaction = sequeatration |
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Definition
occurs when:
there is little moisture or insufficient lytic enzymes. Seen in areas of coagulative or caseous necrosis. Dead tissues act as an irritant -> inflammation response ->fibrous tissue production. Fibrous capsule surrounding a caseous center = a sequestrum. |
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Term
sequelae of necrosis:
erosion and ulceration |
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Definition
desquamation- sloughing of dead cells from the underlying epithelium into a space or lumen.
erosion = loss of epithelial cells only
ulceration = loss of epithelial cells + the basement membrane (exposing the underlying connective tissue) |
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Term
sequelae of necrosis:
organization = repair = scarring |
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Definition
necrotic tissue is invaded by:
1.leukocytes - to digest dead tissue
2.capillaries
3.fibroblasts- repair tissues |
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Term
sequelae of necrosis:
regeneration |
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Definition
| some dead cells are replaced by subdivision of surviving cells. only replicable tissues can regenerate, not post-mitotic tissues such as neurons or cardiac myocytes |
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Term
Gangrene- ischaemic necrosis of the extremities
(typs) |
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Definition
1.dry gangrene
2.moist gangrene
3.gas gangrene |
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Term
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Definition
uncomplicated ischaemic necrosis
ex. frostbite- vasoconstriction due to cold temps. |
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Term
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Definition
| when ischaemic necrosis becomes complicated by bacterial infection. Tissues are dark and foul smelling. Bacteria can invade because the body's defense mechs. are inactivated |
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Term
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Definition
| a special form of moist gangrene caused by gas producing bacteria (ex. Clostridia)which are spore forming saprophytes. they cannot grow in healthy tissue, but once allowed to proliferate they produce powerful necrotizing exotoxins, inducing necrosis in nearby healthy tissue. Bubbles of gas form. |
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Term
| morphological appearance of gangrene |
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Definition
cool to the touch, unresponsive to stimuli, does not bleed, has a line of demarcation and is dark in color. Color is due to:
1.anoxic blood (dark red/blue)
2.haemosiderin (golden brown)-RBC breakdown pigments
3.iron sulphide (dark green)- derived from the breakdown of -SH containing AA producing hydrogen sulphide, which further reacts with Fe+ from heme to make iron sulphide. |
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Term
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Definition
1.sloughing off the part with healing tissue = raw area
2. death from toxaemia- toxins produced by body protein decomp which are absorbed into the blood steam or lymphatics |
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Term
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Definition
programmed cell death.
occurs without initiating inflammation or the release of cellular contents |
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