Necrosis is irreversible injury and death of cells and living tissue. There are several patterns of necrosis that occur in tissues including coagulative, liquefactive, caseous, fat and gangrenous necrosis. Coagulative necrosis involves the maintenance of cell outlines but loss of cellular details. Liquefactive necrosis results in the disintegration and liquefaction of dead cells. Caseous necrosis converts dead tissue into a granular mass resembling cottage cheese.
2. DEFINITION
NECROSIS
Its an irriversible injury
produced by enzymatic
digestion of dead cellular
elements
APOPTOSIS
Its a vital process that helps
eliminate unwanted cells-an
internally programmed series
of events causing cell death
4. MORPHOLOGY OF NECROSIS :
1.Cellular swelling or rupture
2.Denaturation and coagulation of cytoplasmic proteins
3.Breakdown of cell organelles
4.Breakdown of nuclear DNA
5. PATTERNS OF NECROSIS IN TISSUES
OR ORGANS
As a result of cell death the tissues or organs display one of
these six macroscopic changes:
1.Coagulative necrosis
2.Liquefactive necrosis
3.Caseous necrosis
4.Fat necrosis
5.Gangrenous necrosis
6.Fibrinoid necrosis
6. PATTERNS OF NECROSIS IN TISSUES
OR ORGANS
1.Coagulative necrosis:
the outline of the dead cells are maintained and the
tissue is somewhat firm.
Example: Myocardial infarction, liver, kidney, thermal
burns
2.Liquefactive necrosis:
the dead cells undergo disintegration and affected
tissue is liquefied.
Example: Brain
7.
8. GROSS - NECROSIS
• Affected areas look white, grey or yellow in colour.
• Have a cooked meat appearance.
• Sharply demarcated (by red zone) from healthy tissue.
• In case of gangrene the area is green, orange or black
(iron sulphide)
9. MICROSCOPY - NECROSIS
The microscopic changes of necrosis vary with the type of
necrosis. Some general changes of necrosis in the cytoplasm
are:
Eosinophilia: The cytoplasm stains darker red in colour.
Swelling and vacuolation: The cells are swollen and contain
different types of vacuoles.
Changes in the nucleus: The nucleus may show condensation
(Pyknosis), fragmentation (karyorrhexis) and may disappear
(karyolysis).
10. COAGULATIVE NECROSIS
Most common type of necrosis.
Architectural outlines persist but cellular details are lost.
Type of tissue can be recognized.
Denaturation (coagulation) of structural and enzymic
proteins blocks proteolysis.
11. CAUSES OF COAGULATIVE NECROSIS
• Ischemia due to thrombosis/ embolism as in infarcts.
• Bacterial toxins e.g. Fusobacterium necrophorum in livers in
cattle.
• Muscular dystrophy due to deficiency of selenium and vit. E
in cattle and sheep.
• Necrosis of renal epithelium due to poisoning from
mercuric salts.
12. Gross appearance:
• Necrotic area is firm, opaque with cooked meat appearance.
• It is sharply demarcated from the healthy areas.
Microscopic appearance:
• Architectural outlines are present; cellular details are
lacking.
Result:
• Dead tissues remain in the body for a long period,
ultimately removed by macrophages.
21. CASEOUS NECROSIS
Dead tissue is converted into a homogenous, granular mass
resembling cottage cheese.
Cause:
Associated with lesions of Mycobacterium tuberculosis, the
cause of caseous lymphadinitis.
22. Gross appearance:
The area of necrosis is amorphous, granular, friable, white-
grey resembling cottage cheese.
The caseous mass is enclosed within a connective tissue
capsule.
Microscopic appearance:
The necrotic tissue is amorphous, granular mass enclosed
inside a zone of granulomatous inflammation, containing
macrophages. No architectural or cellular details are seen.
Calcification commonly occurs in the necrotic areas.
26. LIQUEFACTIVE NECROSIS
• Rate of dissolution of the necrotic cells is faster than the
rate of repair. Usually results in an abscess secondary to
bacterial infection.
• Hydrolysis of dead tissues or cells rapidly destroyed by
lysosomal enzymes from neutrophilic leukocytes (i.e.,
bacterial infections), or clostridia or snake poison.
• Liquefactive necrosis that is caused by neutrophilic
leukocytes is called pus.
