Explain the Concept of Negative Feedback .

The Concept of Negative Feedback

Most control systems of the body act by negative feedback. It can be defined as the change of a variable that is opposed by responses which tend to reverse this change. For instance, in the regulation of carbon dioxide concentration, a high concentration of carbon dioxide in the extracellular fluid
increases pulmonary ventilation. This in turn decreases the extracellular fluid carbon dioxide concentration because the lungs expire greater amounts of carbon dioxide from the body. In other words the high concentration of CO2 initiates events that decrease the concentration towards normal, which is negative to the initiating stimulus. Conversely if concentration of CO2 falls too low this causes feedback to increase the concentration. This response also is negative to the initiating stimulus.
In the arterial pressure-regulating mechanisms, a high pressure causes a series of reactions that promote a lowered pressure and vice versa. A rise of body temperature in mammals and birds also produces responses which return body temperature to its original desired value. Therefore , in general, if some factor becomes excessive or deficient, a control system initiates negative feedback, which consists of a series of changes that return the factor towards a certain mean value, thus maintaining homeostasis. Negative feedback therefore maintains stability in physiological systems.

Positive Feedback

In positive feedback systems, an initial change in a particular variable results in further change. Positive feedback therefore does not lead to stability but to instability and often death. For example, the heart of a healthy human being pumps about 5 liters of blood per minute. If the person is suddenly bled 2 liters of blood, the amount in the body is decreased to such a low level that not enough blood is available for the heart to pump effectively. As a result the arterial pressure falls and the flow of blood to the heart muscle through the coronary vessels decreases. This results into weakening of the heart and also a weakening of the pumping action, a further decrease in coronary blood flow, and still more weakness of the heart. The cycle repeats itself again and again until death occurs. Note that each cycle of the feedback results into further weakening of the heart. In other words the initiating stimulus causes more of the same, which is positive feedback

Positive feedback can sometimes be useful to the body. Blood clotting is an example of a valuable use of positive feedback. When a blood vessel is ruptured and a clot begins to form, multiple enzymes called clotting factors are activated within the clot itself. Some of these enzymes act on other inactivated enzymes of the immediately adjacent blood, thus causing more blood clotting. This process continues until the hole in the vessel is plugged and bleeding no longer occurs. Uterine contractions during birth are another example of positive feedback that is valuable. When uterine contractions become strong enough for the fetus’s head to begin pushing through the cervix, stretch of the cervix sends signals through the uterine muscle back to the body of uterus, causing even more powerful contractions, and the fetus is expelled.

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marto answered the question on April 16, 2019 at 07:03