The Differences Between Apoptosis and Necrosis

Apoptosis and necrosis are two terms that refer to two ways that cells die. However, they're not the same. Cells can die in a programmed, nature manner or undergo an extensive dying process. Learn more here!

Reviewed and approved by the pharmacist María Vijande.

Written by María Vijande

Last update: 27 May, 2022

Cell death in human tissues and in that of other multicellular organisms is a normal occurrence. In fact, apoptosis and necrosis are two terms that refer to two ways that cells die. The number of cells in different tissues is determined by a homeostatic balance between the creation of new cells and the death of depleted cells.

In the case of apoptosis, it’s a natural process that’s genetically programmed and responds to homeostatic mechanisms. However, there are failures in the activation of apoptosis that can trigger problems in the body.

On the other hand, necrosis is an acute process produced by a massive cellular injury or disease.

Cellular mechanisms of apoptosis and necrosis

Overall, it can occur due to many and varied causes. These include loss of function, mechanical damage, infections, chemical agents, or lack of nutrients, among others.

However, the difference between apoptosis and necrosis is the mechanism by which they occur. We’ll describe the characteristics of apoptosis and necrosis below.

Necrosis

First, necrosis occurs acutely, in a non-physiological manner, due to aggression that causes injury to a significant portion of the tissue. It can occur, for example, in some of these situations:

• The center of infarcted tissue.
• In an area of ischemia (without sufficient blood).
• In the area of a toxin injury.

The action of toxins, a lack of oxygen, massive aggression, or any other situation that generates a decrease in ATP (adenosine triphosphate) can trigger the process of necrosis. ATP is a substance that provides energy to cells and without which they can’t perform any of their functions.

This lack of energy causes the cell organelles, which are different structures that perform vital functions in the cell, to become disorganized. Likewise, the cytoplasm, which is the part of the interior of the cells where the different organelles are located, breaks down. Some of the alterations that necrosis produces in cell organelles are:

• The endoplasmic reticulum (in charge of the synthesis of molecules and the transport of substances) and the mitochondria dilate.
• The chromatin (where we find the cell’s DNA) dissolves.
• The cell membrane loses continuity and eventually ruptures.

During necrosis, the DNA splits into random, irregular fragments. And as a consequence of the loss of continuity of the cell membrane, the contents of the cell’s interior spill out of the cell.

This process causes the cells of the immune system to move to the area where the necrosis has occurred, triggering an inflammatory process.

Apoptosis

This cell death process can occur naturally or as the result of an illness, but without ATP loss. This is because, for apoptosis to take place, it needs to consume energy.

A genetically and synthetically motivated command initiates a series of biochemical reactions that lead to changes in cell morphology and, ultimately, to cell death. All of this is a response to physiological or pathological events.

In cases where apoptosis is the result of an illness, it’s because the disease motivates the cell to induce its own death. Histologically, it involves the condensation or shrinkage of the cell organelles found in the cytoplasm.

The chromatin doesn’t break down but condenses to form apoptotic bodies. The immune system doesn’t degrade this condensed chromatin, so inflammation doesn’t occur. Rather, neighboring cells capture it. This process occurs in isolated cells and not in whole areas of tissue.

In conclusion

In conclusion, apoptosis and necrosis differ in the stimulus that triggers both processes. There are also differences in the energy requirement, histology, and DNA breakdown.

In both processes, cell organelles and the cell membrane are altered. While apoptosis is occasional and develops in isolated cells, necrosis, on the other hand, becomes evident in entire portions of tissues.