cell death 1

what is cell death?

the loss of biological activities and structure of a cell as a result of irreversible injury.

what does cell death depend on?

the nature of the injury and the severity of the injury

what are the main types of cell death?

necrosis and apoptosis 

what is necrosis?

premature, uncontrolled cell death of living cells or tissues. it is always a pathological process. it is the death of a group of cells in a living tissue

what is apoptosis?

programmed cell death. it may be physiological or pathological processes

what is the mechanisms of necrosis?

1. ATP depletion and mitochondrial damage 

2. calcium release 

3. accumulation of reactive oxygen species 

4. increased permeability of cellular membranes 

what is the first change that occurs in necrosis?

cytoplasmic changes, specifically cytoplasmic eosinophilia due to release of RNA from the nucleus 

what are the three nuclear changes that occur?

1. karyolysis 

2. karyorrhexis 

3. pyknosis 

what is karyolysis?

the dissolution or disintegration of nuclear chromatin 

what is karyorrhexis?

fragmentation of nuclear chromatin 

what is pyknosis?

condensation of nuclear chromatin

what order do the nuclear changes occur in necrosis?

1. pyknosis

2. karyorrhexis

3. karyolysis

what are the types of necrosis?

1. coagulative

2. liquefactive

3. caseous

4. fat

5. fibrinoid

6. gangrenous

what is coagulative necrosis?

a form of necrosis in which the cell shape and tissue structure are preserved by coagulation of proteins but the nucleus disappears, taking on a ghostly appearance 

coagulative necrosis is most commonly associated with what type of injury?

ischemic injury

coagulative necrosis from the ischemic infarction occurs in all organs except?

the brain

coagulative necrosis is most frequent in what organs?

heart, kidney, spleen and limb

what are characteristics of coagulative necrosis tissue?

dry, pale, yellow and firm. it is wedge shaped in organs like the kidneys and spleen 

what is liquefactive necrosis?

cell death and fluid formation in cells. microbes stimulate the accumulation of inflammatory cells (neutrophils) and the enzymes of leukocytes digest (liquefy) the tissue, transforming the tissue into a viscous liquid that is eventually removed by the phagocytes 

what is a characteristic of liquefactive necrosis?

the occurrence of abscesses, or pockets of pus. it is creamy yellow and initiated by acute inflammation, such as a bacterial infection

how does liquefactive necrosis occur?

due to pyogenic bacterial infections or ischemic injuries in the brain. it is caused by bacteria such as staphylococcus and streptococcus 

what is caseous necrosis?

a distinctive type of necrosis which shows combined features of coagulative and liquefactive necrosis 

where is caseous necrosis most often caused by?

the foci of mycobacterium tuberculous infection

what organs is tuberculosis most commonly found in?

the lymph nodes and lungs

where is the term caseous derived from?

it is also known as cheese-like. it is derived from the friable, yellow-white appearance of the necrosis on gross examination 

how does caseous necrosis differ from coagulative necrosis?

the tissue structure is completely obliterated and cellular outlines cannot be seen

microbacteria is one of the primary causes of which forms of necrosis?

• liquefactive necrosis 

• caseous necrosis 

what is fat necrosis?

it refers to the focal areas of fat destruction, which affect adipose tissues 

what are the two types of fat necrosis?

1. traumatic

2. enzymatic

traumatic fat necrosis 

it occurs in tissues with high fat content, such as the breasts or thighs, following severe trauma 

enzymatic fat necrosis 

occurs in adipose tissue around acutely inflamed pancreas

how does enzymatic fat necrosis occur?

in pancreatitis the enzymes, one of them being lipase, leak from acinar cells and cause tissue damage. lipase destroys fat cells and liberates free fatty acids which combines with calcium to form grossly visible chalky white areas

the process that occurs in enzymatic fat necrosis is known as what?

fat saponification 

what is fibrinoid necrosis?

this is a special, rare form of necrosis usually seen in immune reactions involving the blood vessels. this pattern of necrosis is prominent when complexes of antigens and antibodies are deposited in the walls of arteries 

what is gangrenous necrosis?

massive type of necrosis with superadded putrefaction

what are the two types of gangrene?

dry and wet gangrene 

what is a variant of wet gangrene?

gas gangrene 

what causes gas gangrene?

clostridia, which is gram positive anaerobic bacteria 

what is the most common cause of dry gangrene?

arterial occlusion, such as atherosclerosis 

what is the most common site of dry gangrene?

it typically involves a limb and is most common in the distal part of lower limbs, such as the leg, foot or toe 

what is the appearance of dry gangrene?

dry with a shrunken or shriveled and dark brown or black appearance. it resembles the foot of a mummy 

which type of gangrene has a clear line of demarcation?

dry gangrene, with it being between the gangrenous and adjacent normal tissue 

what type of necrosis is dry gangrene?

it is predominantly coagulative necrosis 

what is the primary cause of wet gangrene?

venous blockages, such as a strangulated hernia, intussusception or volvulus 

where are the sites of wet gangrene?

it is typically in moist tissues or organs, such as the bowels, the mouth, lungs, etc. bed sores and diabetic foot are other examples of it due to high sugar content in necrosed tissue, which favors growth of bacteria 

what are the characteristics of wet gangrene?

soft, swollen, putrid and dark with no clear line of demarcation

what type of necrosis is wet gangrene?

it is predominantly liquefactive necrosis 

how does gas gangrene occur?

anaerobic clostridia enters tissues through open contaminated wounds. toxins produced by the bacteria cause local necrosis and edema. they are then absorbed, causing severe systemic manifestations 

between the two types of gangrene, which one is rapid onset and requires immediate medical attention?

wet gangrene, as it spreads quickly and can lead to septic shock if left untreated