Michelle Kelrikh, mjkelrikh@gmail.com
Monday, March 19, 2012
Argument: Positive and Negative Feedback
Shenk asserts that in Kenya, running became a way of life for so many because of the large amount of prize money. The "instant-life changing wealth" is what caused "success to breed more success" causing for higher and higher benchmarks of achievement in the realm of running. This meant that each generation of better runners within Kenya created a "positive feedback loop analogous to technological innovation in Silicon Valley...and talents in other highly successful microcultures." (105.) What other positive and negative feedback loops might be associated with the GxE paradigm? What relationship might this have with the biological theme of evolution?
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One positive feedback loop that we've learned about is is the presence of oxytocin in pregnant mothers giving birth. Oxytocin causes contractions necessary to get the baby out of the birth canal and the presence of oxytocin in the blood causes the hypothalamus to produce more oxytocin. Another positive feedback loop is blood clotting. Activated platelets in the blood releases chemicals to activate other platelets, causing a rapid cascade and the formation of a blood clot. Other positive feedback loops include inflammatory immune responses which we're learning in class currently. Hormones such as cytokines are used in paracrine signaling when pathogens invade the body, "activated macrophages and mast cells at the injury site release signaling molecules that act on nearby capillaries... allowing fluid containing... phagocytic cells that digest pathogens and cell debris at the site" (Campbell 935). The signaling molecules, such as chemokines, are a chemical messenger to make cells to do certain things and go to certain places by their following a concentration gradient to the location and congregating at that spot (eventually forming a scab). The histamine, which is a chemical that widens capillaries to increase blood flow also operates on a positive feedback loop. The macrophages which engulfs pathogens also functions on a positive feedback loop; the presence of macrophages stimulates the production of more macrophages because of the cytokines that change gene expression. This is related to the GxE paradigm because the environment with the pathogens can cause the body to react that way when it enters the body and this is related to the biological theme of evolution because this is the one of the most efficient way for the body to deal with an invasion of pathogens with the least energy output.
ReplyDeleteA common negative feedback loop is hormone secretion. When gland X releases hormone X, this stimulates target cells to release hormone Y and then when there's an excess of hormone Y, gland X senses this and stops its release of hormone X. Another example of negative feedback is body temperature regulation. The hypothalamus monitors the body temperature and once it senses an increase or decrease in body temperature, stimulation of sweat glands or muscles to shiver occurs until body temperature is back at normal level and then sweating and shivering stops. Breathing rate is also an example of negative feedback. If there's too much carbon dioxide in the body, the lungs are signaled to increase their activity and expel more carbon dioxide. And once the carbon dioxide levels have decreased, the person stops breathing so hard. These types of regulation are importantly tied to evolution because it impacts evolutionary selection pressure. For example, the breathing rate feedback loop and the oxytocin one can be very helpful in surviving and reproducing, which promotes those feedback loops in future generations.
^ (mindy shaw, mindyshaw95@yahoo.com)
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