Necrosis

Question 1

What is necrosis?

Answer 1

A form of cell death - unprogrammed - due to cell injury

Question 2

Which process occur within a necrotic cell, which are responsible for the morphological appearance of necrosis in tissues

Answer 2

The denaturation of intracellular proteins and the enzymatic digestion ofthe lethally injured cell

Question 3

Why does necrosis trigger inflammation?

Answer 3

The cell membrane ruptures and the content of the cell seeps out - eliciting inflammation

Question 4

Describe some morphological features of a necrotic cell

Answer 4

Discontinous plasma membrane
Dilated mitochondria
Myelin figgues and amorphous debris in cytoplasm (denatured proteins)

Question 5

What are myelin figures?

Answer 5

These are phospholipid masses which replace dead cells - derived from damaged membranes

Question 6

What is the date of myelin figures

Answer 6

Either phagocytosed or degraded into fatty acids

Question 7

What is the fate of the necrotic cell?

Answer 7

They can become calcified, disappear by phagocytosis or enzymatic digestion by leukocytes

Question 8

What happens to the nucleus of the necrotic cell?

Answer 8

One of the 3:

• Karyolysis (loss of DNA by enzymatic degradation)
• Pyknosis (nuclear shrinkage)
• Karyorhexis (where a pyknotic nucleus undergoes fragmentation)

Question 9

What happens when necrotic cells are not promptly destroyed and reabsorbed?

Answer 9

They attract calcium salts and other minerals and eventually become calcified (dystrophic calcification)

Question 10

Describe coagulative necrosis

Answer 10

Characterised by a firm texture (of the tissue) - since the injury of the tissue denatures also the digestive enzymes hence blocking proteolysis of the dead cells. This type of necrosis is commonly caused by ischemia

Question 11

Describe liquefactive necrosis

Answer 11

Characterised by digestion of dead cells and transformation of tissue into a viscous mass of pus formation from dead leukocytes. Typically caused by microorganism infections

Question 12

Describe gangrenous necrosis

Answer 12

Coagulative necrosis in a limb with inadequate blood supply (called wet gangrene if there is bacterial superinfection with liquifactive necrosis)

Question 13

Describe caseous necrosis

Answer 13

Necrosis + granuloma formation. Typical in TB infection

Question 14

Describe fat necrosis

Answer 14

This is due to the release of pancreatic lipases (in acute pancreatitis) - causing focal areas of necrotic and calcified fat cells, surrounded by an inflammatory border

Question 15

Describe Fibrinoid necrosis

Answer 15

This is necrosis caused by an immune reaction that forms deposits within vessels together with fibrin (immunologically mediated vasculitis)