Cell death in human tissue and in other multicellular organisms is a normal occurrence. In fact , apoptosis and necrosis are two terms that refer to two ways cells die. The number of cells in different tissues is determined by a homeostatic balance between the formation of new cells and the death of depleted cells.
In the case of apoptosis, it is a natural process that is genetically programmed and responds to homeostatic mechanisms. However, there are errors 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
Cell death is the cessation of the vital functions of a cell. This is the result of irreversible morphological, functional and chemical changes.
Overall, it can occur due to many and varied causes. These include loss of function, mechanical damage, infections, chemical agents or lack of nutrients.
However, the difference between apoptosis and necrosis is the mechanism by which they arise. We will describe the properties of apoptosis and necrosis below.
First, necrosis occurs acutely, in a non-physiological manner, due to aggression that causes damage to a significant portion of the tissue. For example, it may occur in some of these situations:
- Center of infarcted tissue
- In an area with ischemia (without sufficient blood)
- In the area with a poison damage
The effects of toxins, lack of oxygen, massive aggression or other situations that generate a reduction in ATP (adenosine triphosphate) can trigger the process of necrosis. ATP is a substance that gives cells to cells and without which they can not perform any of their functions.
This lack of energy causes the cell organelles, which are various 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 various organelles are located, is broken down. Some of the changes that necrosis produces in cell organelles are:
- The endoplasmic reticulum (responsible for the synthesis of molecules and the transport of substances) and the mitochondria expand
- The chromatin (where we find the cell’s DNA) dissolves
- The cell membrane loses continuity and eventually ruptures
During necrosis, DNA divides into random, irregular fragments. And as a consequence of the loss of continuity in the cell membrane, the contents of the cell interior squirt out of the cell.
This process causes the cells in the immune system to move to the area where necrosis has occurred, triggering an inflammatory process.
The process of apoptosis was discovered in 1972 and was the focus of histological studies until the late 1980s. However, it was not until the 1990s that researchers were able to discover the genetic and molecular mechanisms involved in the process.
This cell death process can occur naturally or as a result of a disease, but without ATP loss. This is because in order for apoptosis to take place, it must consume energy.
A genetically and synthetically motivated command initiates a series of biochemical reactions that lead to changes in cell morphology and eventually cell death. All this is a response to physiological or pathological events.
In cases where apoptosis is the result of a disease, it is because the disease motivates the cell to induce its own death. Histologically, it involves condensation or shrinkage of the cell organelles present in the cytoplasm.
The chromatin does not break down, but condenses to form apoptotic bodies. The immune system does not break down this condensed chromatin, so inflammation does not occur. Rather, neighboring cells capture it. This process occurs in isolated cells and not in entire areas of tissue.
Apoptosis and necrosis: To conclude
Finally, apoptosis and necrosis are different in the stimulus that triggers both processes. There are also differences in energy requirements, histology and DNA breakdown.
In both processes, cell organelles and the cell membrane change. While apoptosis is sporadic and develops in isolated cells, necrosis, on the other hand, becomes apparent throughout parts of the tissue.