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Apoptosis is normal cell death in living organisms, necessary for normal development. It is distinct from necrosis and has several stages, including the breakdown of the cell nucleus and consumption by phagocytes. Failure to complete apoptosis can cause deformities and tumors. The study of apoptosis is important for understanding cell death and its applications in medicine.
Apoptosis is the term used to describe the generally normal cell death in living organisms. As new cells regenerate, cell death is a normal and constant process in the body. Human embryos, for example, have many more cells than adult humans. As the embryo develops, certain cells are selected for execution so that normal development takes place. When these cells fail to undergo apoptosis, they can cause deformities in the growing embryo.
This term should not be confused with necrosis, cell death from disease or infection. Apoptosis is part of the function of the cell in the body. When the processes are incomplete, this can lead to the development of both benign and malignant tumors, for example.
Apoptosis has several distinct stages. In the first stage, the cell starts to become round due to the protein in the cell being eaten by the enzymes that become active. Subsequently, the DNA in the nucleus begins to shed and shrink. The membrane surrounding the core begins to degrade and eventually no longer forms the usual layer.
Because the cell nucleus is no longer protected, the cell’s DNA breaks down into irregular fragments. The nucleus is now broken into many bodies with irregular amounts of DNA. The cell itself goes through a process called blebbing, where parts of the cell begin to break down. Finally, the cell is completely broken up and consumed by small cells called phagocytes.
There is danger if this final stage of phagocytic digestion into apoptosis is not completed. Undigested cell fragments can accumulate in the body and have been shown to cause death in mouse embryos and mouse newborns.
Apoptosis can occur due to signals within the cell (intrinsic) or signals outside the cell (extrinsic). When it is caused by intrinsic signals, it can be the result of a lack of sufficient nourishment for the cell or damage to the DNA in the nucleus. Extrinsic apoptosis can occur in response to a virus or to treatments such as chemotherapy. Sometimes, a cell initiates the process in an attempt to fight off a virus, such as HIV.
The study of apoptosis has become quite important, and most of our current understanding of cell death is the result of studies conducted in the 1990s and present day. Being able to induce cell death is desirable, for example, when attempting to kill tumor tissue. Furthermore, understanding how the process works favors research on the study of stem cells and their possible applications in medicine.
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