system
Given the following post, respond as if you're commenting on Reddit:
human
Why does a lack of oxygen cause cell death instead of the cell 'winding down' into some kind of stasis?
gpt
Dug up some old lecture notes about this. If there's any factual errors, please tell me.

Aight, so, in the context of the human body necrosis is the word for uncontrolled cell death (things leak out of the cell, causes inflammation), while apoptosis is the word for controlled cell death (everything packed up in neat vesicles for further breakdown). Severe hypoxia will lead to necrosis eventually.

Essentially, what happens when a cell is exposed to hypoxia is that it starts switches over to anaerobic metabolism. This, however, produces way less ATP (energy) than aerobic metabolism, and also produces lactate as a byproduct. Insufficient ATP leads to the ion-pumps on the surface of the cell not functioning, and thus an electrolyte imbalance (as the cell normally needs to spend energy to maintain the differing concentrations intra-/extracellularly). The electrolyte imbalance results in net flow of fluid into the cell, and thus cell swelling, due to osmotic effects.

Electrolyte imbalance and lactate accumulation leads to a decreased pH, which in turn leads to wrongly folded proteins (protein folding is a very important and intricate process to ensure functional proteins). Crucially, these misfolded proteins along with the ATP-deficiency means the cell fails to maintain an low intracellular concentration of Ca2+ ions. Ca2+ is important in many of the signaling systems of the human body, and can activate many different enzymes (for instance, phospolipases which break down the cell membrane). High Ca2+ leads to uncontrolled activation of various enzymes, which begin to break down various structures of the cell (this is semi-functional; moderate Ca2+ induces apoptosis while a high conc. induces necrosis). It also disrupts mitochondrial functioning by opening pores in their membrane.

The phospolipases mentioned above also break the membranes around lysosomes, which are intracellular packets containing a lot of catalytic enzymes (as a safeguard, these are supposed to only be active in the presence of the low pH present in lysosomes, but hypoxia leads to acidity as mentioned before) that the cells use to degrade various organic matter.

Tl;dr: cell fails to maintain electrolyte and pH balance, high Ca2+ concentration activates a ton of enzymes haphazardly that begin to break down the cell (among them, lysosome membranes -> leakage of catalytic enzymes into the cytosol), improper electrolyte balance causes cell swelling, mitochondria cease to function -> "point of no return" as ATP cannot be generated even in the presence of oxygen

Edit: updated some things after reading a book.