When a cell gets injured – whether it’s reversible or irreversible – a ton of things happen inside inside the cell. There are so many changes, in fact, that we could write an entire book about them. But everyone would fall asleep within two pages. So let’s make an itty bitty summary, so short that you can’t possibly fall asleep while reading.

The whole process of cell injury starts with mitochondrial injury. ATP decreases inside the cell, so ATP-dependent pumps don’t work well, and sodium and calcium accumulate inside cell. Cellular membranes are damaged due to free radical formation. The ultimate reasons the cell dies are: membrane damage and cytoplasmic calcium accumulation.

Things you see in reversible injury:
– Mitochondrial densities
– Cellular swelling
– Cytoskeletal disruption (microvilli loss, bleb formation)

Things you see in irreversible injury:
– All of the reversible changes, plus:
– Increased eosinophilia (pink color) in cells
– Bigger mitochondrial densities
– Nuclear changes (chromatin clumping, then pyknosis, karyolysis, or karyorrhexis)

All this is important clinically because due to their leaky membranes, injured cells release enzymes and proteins into bloodstream. In certain conditions, like myocardial infarction and hepatitis, you can measure the blood level of these enzymes to get an idea of the magnitude of cell death (if the enzyme level is very high, it means lots of cells are dead/dying and the patient is in danger).

Still awake? Good! Then go read Robbins!

Photo credit: Snowpeak (, under cc license.