Describe the negative and positive feedback loops, and discuss how feedback mechanisms regulate each of the following. The menstrual cycle in nonpregnant human female. Blood glucose levels in humans.

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Describe the negative and positive feedback loops, and discuss how feedback mechanisms regulate each of the following. The menstrual cycle in nonpregnant human female.  Blood glucose levels in humans.


Negative feedback loops occur when the substrate cause a decrease in the hormone that is stimulating it keeping the substrate at a constant or near constant level. For example estrogen and FSH. This can also happen if the substrate increases the hormone which regulates its excretion. For example calcium and calcitonin or glucose and insulin.


Positive feedback loops occur when the stimulus or substrate amplifies the response causing an increae rather than a decrease in the level of substrate. One example of a biological positive feedback loop is the onset of contractions in childbirth. When a contraction occurs, the hormone oxytocin is released into the body, which stimulates furthur contractions. This results in contractions increasing in amplitude and frequency. Another example of a biological positive feedback loop is the process of blood clotting. The loop is initiated when injured tissue releases signal chemicals which activate platelets in the blood. An activated platelet releases chemicals which activate more platelets, causing a rapid cascade and the formation of a blood clot.

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