In endogenous apoptosis, the body initiates cell death of individual cells of its own body. In every organism, this process takes place to rid the body of diseased, dangerous, and no longer necessary cells. Disturbances in the body’s own apoptosis can lead to various diseases such as cancer or autoimmune diseases.
What is apoptosis?
The programmed cell death of body cells is called endogenous apoptosis. In this process, body cells that are no longer needed by the organism die. The programmed cell death of body cells is called endogenous apoptosis. In this process, body cells die off that the organism no longer needs or that can become dangerous for it. Within each cell there are inactive suicide factors, which are activated when apoptosis is to be initiated. In contrast to necrosis, however, apoptosis is a programmed cell death. During this process, no cellular components escape to the outside. Before the onset of apoptosis, the corresponding cells are first separated from the cellular structure of the tissue. Then, an intracellular degradation of chromatin, proteins, and cell organelles begins, causing the cell to shrink. Externally, blistering of the cell membrane occurs. The remaining cellular components are immediately disposed of by phagocytes. The entire process of endogenous apoptosis causes only certain cells to die. Neighboring tissue is usually not affected.
Function and task
Endogenous apoptosis is an absolutely vital process for the organism. It ensures the undisturbed function of healthy and functional cells. Apoptosis takes place throughout life. Especially during the development of the organism, the constant selection of body cells must be ensured. The differentiation of body organs could not function accurately without simultaneous apoptosis. However, there must always be a certain relationship between the formation and death of cells. In an adult organism, cell formation and cell death are in balance. Old cells are replaced by young cells. New cells are formed only by cell division. If there were no apoptosis, the number of cells would continue to increase. Therefore, it is necessary that cells also die selectively all the time. In the growth phase, apoptosis ensures that only those cells that are useful to the organism continue to multiply. In sick, old and less effective cells, the suicide program is activated. For example, in order to ensure the correct interconnections in the brain, up to 50 percent of all nerve cells die again even before birth. In the adult organism, apoptosis serves, among other things, to control the number of cells and the size of organs, to break down harmful and unnecessary cells of the immune system, to rejuvenate certain tissues, to eliminate degenerate cells or to select germ cells. To date, two pathways for the initiation of apoptosis have been discovered. A distinction is made between type I and type II apoptosis. In type I apoptosis, also called extrinsic pathway, the initiation of the process occurs externally through the binding of a ligand to a receptor of the TNF receptor family. The second pathway (intrinsic pathway) begins inside the cell and is triggered, among other things, by damage to DNA. In both cases, a cascade of enzymes (caspases) responsible for the degradation of endogenous organelles, proteins and chromatin is initiated. In contrast to the disposal of necrotic cells, the subsequent elimination of cellular components by phagocytes proceeds without inflammatory processes. The balance between controlled cell death, permanent cell renewal and removal of dead cell components is of existential importance for the organism. Disruption of this balance can lead to severe health problems.
Diseases and ailments
Disturbances in the body’s apoptosis play a role in many diseases such as cancer, autoimmune diseases, and viral diseases. For example, when a body cell is infected with a virus, it immediately begins producing more viruses due to the incorporation of viral genome into the DNA. In most cases, the infected cells react with apoptosis. To prevent this, many viruses have developed a counter-strategy. They often reprogram the cell to produce apoptosis-inhibiting substances.The cell does not die and produces more and more viruses, which in turn infect other cells. Antivirals are designed to intervene in the mechanism at precisely this point. Sometimes not only the cells attacked by viruses are eliminated, but also the neighboring tissue. This exaggerated effect is, among other things, also the explanation for the extensive liver damage in viral hepatides, although only a few liver cells are attacked by viruses. In autoimmune diseases, immune cells attack and destroy the body’s own cells. Here, too, faulty processes in apoptosis play a role. The thymus represents the control organ for immune cells. All lymphocytes have special receptors that react only to certain antigens. In the thymus it is tested with which antigens the receptors bind. If they react with the body’s own antigens, the corresponding cell is sorted out and caused to die via apoptosis. If the selection process does not function properly, too many autoaggressive immune cells get through and later cause an autoimmune disease. In another mechanism, it was discovered that the dead cells are removed too slowly by phagocytes. The immune cells that react in the meantime also attack healthy cells. In cancer, on the other hand, apoptosis is reduced, so that only cell renewal occurs without programmed cell death.
