Lecture 6 - Lethal Cell injury

Question 1

What could happen to cell membranes and cell staining in irreversible cell injury?

Answer 1

• Irregular contours

- Eosinophillia as a result of released protein into the cell

Question 2

Define necrosis

Answer 2

The spectrum of morphological changes following cell death or tissue death. Always a pathological process

Question 3

When do you see microscopic changes in cells undergoing necrosis, and what is the sequence of nuclear changes you will see?

Answer 3

-4-12 hours

• Nucleus will go from normal, to Pyknosis as a result of shrinkage, darkening and condensation (black dot). From there, to Karyorrhexis, which is breakdown of the nucleus. This is followed by Karyolysis, where the nucleus is gone
• Throughout this process, the cell will become more and more eosinophilic

Question 4

What are some other microscopic changes you will see in necrotic tissue?

Answer 4

Cytoplasmic vacuolation
Eosinophilia
Cell membrane blebbing/rupture

Question 5

Describe coagulative necrosis

Answer 5

• Most common type
• Usually follows ischaemia, which causes an infarct (localised necrotic area). Tissue is softer than normal, and either more pale (pale infarct) or haemorrhagic (red). Over time, a haemorrhagic border will develop around a pale infarct.
• The cellular architecture is preserved, and cell outline remains for days/weeks. –There is a delayed breakdown of cells, and an inflammatory response.
• Histologically you might see pink cytoplasms still in the shape of cells, missing nuclei.

Question 6

Describe colliquative necrosis

Answer 6

• The necrotic cell releases powerful hydrolytic enzymes, as well as inflammatory exudate - particularly neutrophils. This leads to liquefaction of the entire cells. Later on, there is an inflammatory reaction and liquid material is removed by macrophages, leaving a cystic space, often with a fibrous peripheral border.
• Cellular architecture almost completely disintegrates
• Occurs in two main settings: the brain, or an abscess cavity in the lung

Question 7

Describe Caseous necrosis

Answer 7

-Almost exclusively in TB patients
-Has a white, cheesy appearance
Microscopically is an amorphous, granular debris, lacking in cell detail and outline. H&E sections will show eosinophilia.
-Usually have granulomatous adjacent inflammatory reactions i.e. giant cells and macrophages everywhere
-Histological sections will show the absence of cell outlines and tissue destruction

Question 8

What is the difference between wet, gas and dry gangrene?

Answer 8

• Wet gangrene is necrosis with superadded putrefaction, usually due to gram negative bacteria
• Gas gangrene is usually due to gram-positive bacteria found in soil, like Clostridium species. It causes crepitant swelling
• Dry gangrene is essentially mummification - tissue is dry and black. Often a result of coagulative necrosis

Question 9

What does fat necrosis look like from a macroscopic perspective?

Answer 9

Chalky deposits, as a result of released fatty acids reacting with calcium

Question 10

What are the outcomes of necrosis dependent on?

Answer 10

The tissue involved: susceptibility to injurious stimuli and ability to regenerate, extent of necrosis, and time elapsed.
Subsequent fibrosis is often seen

Question 11

What is autolysis?

Answer 11

Self-digestion of tissue, ot technically necrosis