NECROSIS
Definition: (Short notes)
It is defined as a localised area of death and degradation of
tissue by hydrolytic enzymes liberated from dead cells.
It is always accompanied by inflammatory reaction.
Causes:
1. Hypoxia
2. Chemical agent
3. Physical agent
4. Microbial agent
5. Immunological injury
Pathogenesis:
Two essential changes bring about irreversible cell injury in
necrosis:
1. cell digestion by lytic enzymes and
2. denaturation of proteins
Types: (Short notes)
1. Coagulative necrosis:
Most common type of necrosis.
Caused by irreversible focal injury, mostly from sudden cessation
of blood flow.
Occurs in organs like heart, spleen, kidney
Causes:
1. Ischemia due to thrombosis/ embolism as in infarcts.
2. Bacterial toxins e.g. Fusobacterium necrophorum in livers in
cattle.
3. Necrosis of renal epithelium due to poisoning from mercuric
salts.
, Gross appearance:
Foci of coagulative necrosis in the early stage are pale,
firm and slightly swollen.
With progression they become more yellowish, softer and
shrunken.
Microscopic appearance:
Conversion of normal cells into their ‘tomb stone’. (cell
outline retained)
The necrosed cells are swollen and appear more
eosinophilic.
The necrosed focus is infiltrated by inflammatory cells and
the dead cells are phagocytosed.
2. Liquefaction necrosis:
Also known as ‘colliquative necrosis’.
It occurs due to degradation of tissue by the action of powerful
hydrolytic enzymes.
Associated with abscess formation.
Commonly seen in: infarct brain and abscess cavity.
Gross appearance:
Affected area is soft with liquefied centre containing necrotic
debris.
Later, a cyst wall is formed.
Definition: (Short notes)
It is defined as a localised area of death and degradation of
tissue by hydrolytic enzymes liberated from dead cells.
It is always accompanied by inflammatory reaction.
Causes:
1. Hypoxia
2. Chemical agent
3. Physical agent
4. Microbial agent
5. Immunological injury
Pathogenesis:
Two essential changes bring about irreversible cell injury in
necrosis:
1. cell digestion by lytic enzymes and
2. denaturation of proteins
Types: (Short notes)
1. Coagulative necrosis:
Most common type of necrosis.
Caused by irreversible focal injury, mostly from sudden cessation
of blood flow.
Occurs in organs like heart, spleen, kidney
Causes:
1. Ischemia due to thrombosis/ embolism as in infarcts.
2. Bacterial toxins e.g. Fusobacterium necrophorum in livers in
cattle.
3. Necrosis of renal epithelium due to poisoning from mercuric
salts.
, Gross appearance:
Foci of coagulative necrosis in the early stage are pale,
firm and slightly swollen.
With progression they become more yellowish, softer and
shrunken.
Microscopic appearance:
Conversion of normal cells into their ‘tomb stone’. (cell
outline retained)
The necrosed cells are swollen and appear more
eosinophilic.
The necrosed focus is infiltrated by inflammatory cells and
the dead cells are phagocytosed.
2. Liquefaction necrosis:
Also known as ‘colliquative necrosis’.
It occurs due to degradation of tissue by the action of powerful
hydrolytic enzymes.
Associated with abscess formation.
Commonly seen in: infarct brain and abscess cavity.
Gross appearance:
Affected area is soft with liquefied centre containing necrotic
debris.
Later, a cyst wall is formed.
