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Overview of signal transduction pathways involved in apoptosis. Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as diseases, localized injury, or the death of the organism of which the cells are part.
This is an example of a locally acting (negative feedback) mechanism. An example of upregulation is the response of liver cells exposed to such xenobiotic molecules as dioxin. In this situation, the cells increase their production of cytochrome P450 enzymes, which in turn increases degradation of these dioxin molecules.
Apoptosis is the programmed cell death of superfluous or potentially harmful cells in the body. It is an energy-dependent process mediated by proteolytic enzymes called caspases, which trigger cell death through the cleaving of specific proteins in the cytoplasm and nucleus. [13] The dying cells shrink and condense into apoptotic bodies.
The highest values are found in the mammals which dive deepest and longest. Volume of blood is generally relatively large in proportion to body mass, and blood haemoglobin content can be increased during a dive from red blood cells stored in the spleen. [103] Body size is a factor in diving ability.
Affected cells then proceed to blebbing, and this is followed by pyknosis, in which nuclear shrinkage transpires. [21] In the final step of this pathway cell nuclei are dissolved into the cytoplasm, which is referred to as karyolysis. [21] The second pathway is a secondary form of necrosis that is shown to occur after apoptosis and budding. [21]
An atrophic factor is a force that causes a cell to die. Only natural forces on the cell are considered to be atrophic factors, whereas, for example, agents of mechanical or chemical abuse or lysis of the cell are considered not to be atrophic factors. Common types of atrophic factors are: [23] Decreased workload; Loss of innervation
AIRE is a transcription factor expressed in the medulla [broken anchor] (inner part) of the thymus. It is part of the mechanism which eliminates self-reactive T cells that would cause autoimmune disease. It exposes T cells to normal, healthy proteins from all parts of the body, and T cells that react to those proteins are destroyed.
A cell undergoing apoptosis shows a series of characteristic morphological changes. Early alterations include: Cell shrinkage and rounding occur because of the retraction of lamellipodia and the breakdown of the proteinaceous cytoskeleton by caspases. [56] The cytoplasm appears dense, and the organelles appear tightly packed. [citation needed]