Apoptosis and necrosis are two terms that describe two ways cells die. However, they are not the same. Cells can die naturally, programmed, or go through a comprehensive death process. Learn more in our article!
Cell death is a normal event in human tissues and other multicellular organisms. Apoptosis and necrosis are two terms that describe two ways cells die. The number of cells in different tissues is determined by the homeostatic balance between the formation of new cells and the death of exhausted cells.
Apoptosis is a natural process that is genetically programmed and responds to homeostatic mechanisms. However, failures in the activation of apoptosis can occur, which can trigger problems in the body.
On the other hand, necrosis is an acute process produced by a major cellular injury or disease.
Cellular mechanisms of apoptosis and necrosis
Cell death is the cessation of vital functions of a cell. This is the result of irreversible morphological, functional and chemical changes.
In general, it can occur due to many and varied causes , including loss of function, mechanical damage, infections, chemicals or nutritional deficiencies.
However, the difference between apoptosis and necrosis is the mechanism by which they occur. Below we will describe the features of apoptosis and necrosis.
Necrosis
First, necrosis occurs acutely, in a non-physiological way, due to aggression that causes injury to a significant part of the tissue. For example, it can occur in some of these situations:
- Center of infarcted tissue.
- In the area of ischemia (without sufficient blood).
- At the site of a toxin injury .
The effects of toxins, lack of oxygen, great aggression or any other situation that causes 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 cannot 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 . Similarly, the cytoplasm, which is the part of the cell interior where different organelles are located, also breaks 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 mitochondria enlarge.
- Chromatin (where we find the cell’s DNA) unravels.
- The cell membrane loses its continuity and eventually ruptures.
During necrosis, DNA is broken into random, irregular pieces. As a result of the loss of continuity of the cell membrane, the contents of the cell spill out of the cell.
This process causes immune system cells to move to the area where necrosis has occurred, triggering an inflammatory process.
Apoptosis
The process of apoptosis was discovered in 1972 and remained the focus of histological studies until the late 1980s. However, it was only in the 1990s that scientists discovered the genetic and molecular mechanisms involved in the process.
This process of cell death can occur naturally or as a result of a disease, but there is no loss of ATP. This is because apoptosis requires energy to occur.
A genetically and synthetically motivated command initiates a series of biochemical reactions that lead to changes in cell morphology and ultimately cell death. All of this is a response to physiological or pathological events.
When apoptosis is the result of a disease, it is because the disease triggers the cell to initiate its own death. Histologically, it involves the condensation or shrinkage of cell organelles located in the cytoplasm.
Chromatin does not break down, but condenses to form apoptotic bodies. The immune system does not degrade this condensed chromatin, so there is no inflammation. On the contrary, neighboring cells capture it. This process occurs in isolated cells, not in entire tissue areas.
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In conclusion
As a result, apoptosis and necrosis differ in the stimuli that trigger each process. There are also differences in energy requirements, histology, and DNA fragmentation.
In both processes, cell organelles and cell membranes are changed. Apoptosis is occasional and develops in isolated cells, while necrosis occurs in all parts of the tissues.
