What's the difference between apoptosis and necrosis?


#1

I know the cells are dying, but what differentiates these two death processes?


#2

Yes, these are both death processes, but they are differentiated firstly by whether or not the death was planned (apoptosis) or accidental (necrosis).

Apoptosis

Apoptosis is a planned cell death. Naturally, cells have a predetermined life span, and when it runs it’s course, they self destruct. This cell death is planned, organized, and intentional. The cell breaks its various components down into organized apoptotic bodies which are neatly wrapped with cell membranes. These little apoptotic bodies are then picked up and easily recycled by macrophages.

With apoptosis, the amount of cell death is not likely extreme in any one region, but rather spread out over the body with a cell here and a cell there, which makes it a lot easier to control and clean up. Because of the neat organized breakdown and the spread out and controlled manner of apoptosis, this process involves no inflammation.

Necrosis

Necrosis is not planned, but accidental cell death. This results most commonly from hypoxia (lack of oxygen) but also damage from chemicals, trauma, etc. The first step in necrosis is typically ischemia which is reversible. The lack of oxygen to the cell results in reduced ATP production and the conversion from aerobic respiration to anaerobic respiration which produces lactic acid. Anaerobic respiration cannot sustain the cell long term and it will eventually run out of ATP to perform it’s necessary functions.

One of the first things to break down is the cell membrane sodium potassium pump which maintains sodium out and potassium in. The pump needs ATP to work, and when there is no more ATP, sodium (along with water) as well as calcium rush into the cell. The sodium and water causes cell swelling, and the calcium starts to break down the integrity of the cell structures. The cell eventually bursts and spills its contents into the surrounding tissues signaling a chemotactic inflammatory response, leading to redness, swelling, fever, pain, leukocytosis, etc.