Cell death and post mortem changes Flashcards
What are the causes of necrosis
Three main causes
* Loss of blood supply
* Non-living agents - chemicals or physical injuries
* Living agents - bacteria, viruses, fungi and parasites
Loss of blood supply in necrosis
Ischaemia- reduced blood supply to a tissue; ischaemic necrosis
Infarction- necrosis of a section of tissue due to an interruption (usually sudden) in blood supply
What do consequences of ischaemia depend on?
- the type of tissue affected
– the type of cell in the tissue - essential functioning cells (parenchyma) are much more susceptible than the connective tissue supportive cells (stroma)
– the metabolic activity of the tissue - very active organs are more susceptible
– whether or not there is a good or potential collateral blood supply
3 ways ischaemia occurs?
- compression of the blood vessel
- narrowing of the vessel lumen due to mural thickening (atherosclerosis)
- blockage of the vessel lumen - causes are thrombi (final stage of blood clot) and emboli (plaque)
How does compression of blood vessels cause ischaemia?
Venous outflow obstructed
– organ swells due to congestion
– swelling impedes arterial flow
– arterial flow stops
– tissue undergoes ischaemic necrosis
– intestinal blood barrier compromised
– bacterial toxins absorbed
* Death (toxaemia)
* intestine friable: prone to rupture
* with peritonitis (inflammation of abdominal membrane)
Appearance of necrotic lesions
in surrounding tissue cells will be damaged but not yet dead -
degeneration
there will also be an immunological reaction to the dead and dying cells - congestion and inflammation
Colour and consistency of necrotic tissue
in contrast to living tissue, dead tissue tends to be paler, partly because there is no circulation in dead tissue
consistency depends on type of agent and tissue
What are the types of necrosis based on macroscopic changes?
- Coagulative necrosis - firm
- Liquefactive necrosis - becomes liquid
- Caseous necrosis - looks like ‘cottage cheese’
- Other types include fat necrosis - hard soap-like appearance and gangrene - usually post necrotic change
What is coagulative necrosis?
Macroscopically: firmer and dryer on the cut surface but still resembles in outline living tissue
Microscopic:
*general architecture of the tissue is
preserved.
* cells may appear larger and their outline may be lost
* the cytoplasm appears structureless and homogenous pink
* nuclear changes
Causes– bacteria which produce toxins, infarction, and viruses
What are microscopic changes in necrosis?
In the nucleus:
Pyknosis - Chromatin clumps and nucleus
becomes dense
Karyorrhexis- (Gk– karyon = nucleus:
rhexis = breaking up) - nucleus breaks up into dense pieces
Karyolysis - (dissolution of the nucleus) nuclear staining with haematoxylin
becomes faint and only the ghost outline of the nucleus remains
In the cytoplasm: stains brighter pink, more eisinophilic
What are types of liquefactive (colliquative) necrosis?
Two types:
Malacia in CNS
Abscesses anywhere in body including CNS
What are abscesses in liquefactive (colliquative) necrosis?
-Pyogenic (pus producing) organisms
– bacteria which cause necrosis and
capable of attracting large numbers of
neutrophils which they also kill
– dying neutrophils release proteolytic
organisms which:
* digest necrotic tissue
* kill further tissue cells
* kill other incoming neutrophils– pus is made up of
* dead and dying neutrophils
* dead tissue
* organisms causing the necrosis
What does caseous necrosis look like?
Microscopic
*loss of normal architecture
*Necrotic tissue contains macrophages and giant cells
These lesions are called granulomas: fungi, parasites and foreign bodies also cause granulomas
What is the pathogenesis of fat necrosis?
Release of enzymes from damaged
pancreas or trauma eg brisket of large
animals
* fat cells die releasing fatty acids
* these combine with Ca++, Na+ and K+
ions to forms soaps
* soaps are foreign to the body
* they provoke a host inflammatory
response
* these foci remain indefinitely and often
calcify – dystrophic calcification
What is sequelae to necrosis?
Chronic:
* Erosions and ulcers
* Chronic abscessation
* Mineralisation
* Gangrene
If healing occurs:
*Repair and fibrosis/scarring
