Cell injury summary

MI-early-histology

Studying cell injury can be a bear! You can easily go down rabbit holes and get lost in details. To help you avoid wasting time, I thought I’d share a few short summaries of cell injury with you. Feel free to use these or not – they are totally optional.

Here are a couple Pathology Student posts on cell injury:
And here’s a little PDF I put together that follows Dr. Dolan’s lecture topics:
And if all that is just too much, here is an über-simplified version. 

1.  Four cell structures are especially vulnerable to injury:

  • Mitochondria
  • Cell membranes
  • The protein synthesis apparatus
  • DNA

2. Cell injury often starts with ATP depletion, which causes calcium to accumulate. Injury can also be induced by free radicals, which damage cell membranes.

Without enough ATP, cell membrane pumps don’t work well, and calcium accumulates inside the cell. This is bad news for three reasons:

  1. It denatures proteins
  2. It poisons mitochondria (makes them open little channels in their membranes which make oxidative phosphorylation fail; also activates pathways that make the cell kill itself)
  3. It activates a bunch of nasty cellular enzymes (like phospholipases, which break down membranes).

3. The bottom line is that there are two main reasons a cell dies:

  1.       Too much cytoplasmic calcium accumulation
  2.       Too much membrane damage.

4.  You can see changes in cells that tell you whether the cell is injured.

Reversible changes include:

  • Cellular swelling
  • Mitochondrial densities
  • Cytoskeletal disruption (e.g., loss of microvilli, formation of cytoplasmic blebs)

Irreversible changes include:

  • Increased eosinophilia (pink color) in cells. Check out the image above of a myocardial infarction: the myocytes are brightly eosinophilic (remember: “red is dead!”).
  • Bigger mitochondrial densities
  • Nuclear changes: pyknosis (a shrunken, dark nucleus), karyolysis (fading of the nucleus), and/or karyorrhexis (fragmentation of the nucleus into little cookie-crumb-like pieces)

 

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