The body maintains homeostasis by negative feedback mechanisms. At first, I thought the term “negative feedback,” sometimes called negative feedback loops, was quite confusing because the word negative itself kind of threw me off. But after a few examples, it made perfect sense because in negative feedback any deviation from the normal range of function is opposed. The change or deviation in the controlled value initiates responses that bring the function of the organ or structure back to within the normal range.

Negative feedback loops have been compared to a thermostatically controlled temperature in a house, where the internal temperature is monitored by a temperature-sensitive gauge in the thermostat. If it is cold outside, eventually the internal temperature of the house drops, as cold air seeps in through the walls. When the temperature drops below the point at which the thermostat is set, the thermostat turns on the furnace. As the temperature within the house rises, the thermostat again senses this change and turns off the furnace when the internal temperature reaches the pre-set point.

Negative feedback loops require a receptor, a control center, and an effector. A receptor is the structure that monitors internal conditions. For instance, the human body has receptors in the blood vessels that monitor the pH of the blood. The blood vessels contain receptors that measure the resistance of blood flow against the vessel walls, thus monitoring blood pressure. Receptors sense changes in function and initiate the body’s homeostatic response.

These receptors are connected to a control center that integrates the information fed to it by the receptors. In most homeostatic mechanisms, the control center is the brain. When the brain receives information about a change or deviation in the body’s internal conditions, it sends out signals along nerves. These signals prompt the changes in function that correct the deviation and bring the internal conditions back to the normal range.

Effectors are muscles, organs, or other structures that receive signals from the brain or control center. When an effector receives a signal from the brain, it changes its function in order to correct the deviation.

 

TERMS

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Control center—The center that receives messages from receptors about a change in the body’s internal conditions and relays messages to effectors to change their function to correct the deviation; in most homeostatic mechanisms, the control center is the brain.

Effector—A muscle or organ that receives messages from the control center to change its function in order to correct a deviation in the body’s internal conditions.

Hormone—Chemical regulator of physiology, growth, or development which is typically synthesized in one region of the body and active in another and is typically active in low concentrations.

Negative feedback loop—A homeostatic mechanism that opposes or resists a change in the body’s internal conditions.

Positive feedback loop—A mechanism that increases or enlarges a change in the body’s internal conditions.

Receptor—A structure that monitors the body’s internal functions and conditions; detects changes in the body’s internal environment.

Set point—The range of normal functional values of an organ or structure.

Source: Homeostasis – Negative feedback – Body, Blood, Internal, and Conditions – JRank Articles http://science.jrank.org/pages/3365/Homeostasis.html#ixzz1huvuKjwa

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