domingo, 8 de mayo de 2011

Hormonal Regulation

Hormones are important to homeostatic regulation because they regulate many cell activities. We are going to see two different regulation:
  • Homeostatic feedback control mechanisms
  • Hormone antagonists.
Feedback control mechanism is a signaling system in which a product or effect of the system controls an earlier part of the system, either by shutting the process down (Negative feedback) or speeding it up (positive feed back). Most feedback mechanisms of the body are negative, only a few are positive.
Negative Feedback:
Negative feedback is a reaction in which the system responds in such a way as to reverse the direction of change. Since this tends to keep things constant, it allows for a process to return from a state of imbalance back to a homeostatic equilibrium. The thermostat is a good example to understand the negative feedback:
An example of negative feedback in the body is the control of blood-glucose concentrations by insulin. A higher amount of glucose in the blood signals the pancreas to release insulin into the blood. Then, the blood glucose concentration decreases and this lower concentration causes a decrease in the secretion of insulin by the pancreas.
Another example of negative feedback is the Regulation of pituitary glands and tropic hormans as you can see in the figure:
Positive Feedback
Positive feedback is a reaction in which the system responds in such a way as to speed up the direction of change. Positive feedback mechanisms are not as common as negative one.
Hormone antagonists
Many hormones work with hormone antagonists to control the concentrations of substances in the body. The hormones have opposite actions on the body and so are called antagonistic.
Insulin and glucagon make up an antagonistic hormone pair. The action of insulin is opposite that of glucagon. When your blood glucose concentration rises sharply after you eat food that contains simple carbohydrates, the increase in blood glucose level stimulates the pancreas to release insulin into blood. In response to signals by insulin most body cells take up glucose, which removes it from the blood, and the blood glucose concentration returns to the set point.
Later, when your blood glucose concentration has dropped below the set point, the decrease in glusose stimulates the pancreas to release glucagon. Glucagon causes the release of glucose from liver cells, which increases your blood-glucose concentration. This antagonistic relationship between the two hormones helps to maintain the narrow range of blood glucose concentration.

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