As your doctor, your local sherrif
or Gil Grissom will tell
you, there are an infinite number of ways to die. And
when it comes to cellular death, there is an entire spectrum of "death
morphologies." This spectrum is anchored at the extremes by two modes of
cellular death that are as different as night and day: necrosis and apoptosis.
The Death Spectrum. Necrosis is messy. Apoptosis is orderly.
Necrosis is your basic
thermodynamic splat. The cell has suffered an overwhelming insult to its
metabolic and structural integrity, and immediately (or very rapidly) loses its
ability to partition ions. It spills lysosomal contents like hydrolases to
digest itself from the inside out, swells up, and oozes all over the place.
This doesn't look very orderly or regulated. It's a mess. In focal ischemia,
this is the type of cell death that is associated with the densely ischemic
("necrotic") core of the infarct, and it's classically associated
with calpain activity. Necrosis comes in a variety of morphological flavors: pale cell change,, ischemic
cell change, and ghosts.
Apoptosis is another
story. Again, the cell has sustained an insult, but in this case it has
maintained enough of its metabolic and structural integrity to keep limping
along. It's still respiring, and it's working hard to maintain at least some
of its electrochemical gradients. The cell looks like it might live. But in
reality, the cell has taken the biomolecular equivalent of the Five-Point
Palm Exploding Heart Technique. It might look okay now, but the hit has
triggered a cascade of processes that are going to slowly, methodically and
inexorably take the cell apart. The process is deliberate, orderly, and
regulated. This is the type of cell death that is associated with the
"penumbra" of the infarct, with delayed
neuronal death, and with the activity of caspases. Apoptosis is characterized
by the formation of apoptotic blebs ,
the absence of inflammatory lysis, and the formation of DNA ladders.