Sunday, March 9, 2008
Enlarged Stomach During Ultrasound
Introduction to
By: Lionel Perez Valenzuela
why cells undergo apoptosis?
There are two possible answers:
1. Programmed cell death is as necessary for normal development and mitosis.
Examples:
1a. Every second the human body produces 100,000 cells per mitosis and a similar number die by apoptosis.
1b. The death of cells that have already served their purpose. The cells of the tail of tadpoles that suffer metamorphosis in frogs or toads, undergo apoptosis.
1c. Massive cell death. During early development of the nervous system (in the process killed more than 50% of neurons) survive only those who have made the correct synapses.
1d. During the formation of body structures. As in the formation of fingers in the fetus, there is tissue death that is between them (interdigital mesenchymal tissue).
1e. In the endometrial cycle of women. The fall of the uterine lining during menstruation occurs apoptosis.
2. Cell death is necessary to destroy cells that represent a threat to the body.
Examples:
2a. Virus-infected cells. One of the methods by which cytotoxic T cells, kill virus-infected cells is by inducing apoptosis (we know that some viruses in turn take countermeasures to prevent it).
2b. Immune system cells. autoreactive cells of the immune system are removed by apoptosis. When it does not, by defects in the apoptotic machinery, the immune system cells attack the body itself. Autoimmune diseases occur then, as the lulpus erythematosus and rheumatoid arthritis, among others.
3c. Cells with damaged DNA. The damage to the cell's genome can:
a) Loosen normal embryonic development resulting in birth defects,
b) promote uncontrolled cell division leading to cancer proliferation.
now know that cells respond to DNA damage through increased production of p53 protein. The p53 tumor suppressor gene is a potent inducer of apoptosis.
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