Positive feedback system
a. Definition lithe initiating stimulus causes more of the same is called positive feedback system.
b. Example The heart of the normal human being pumps about 5 liters of Mood per minute. However, if the person suddenly bleeds 2 liters, the amount of blood in the body is decreased to such a low level that not enough is available for heart to pump effectively. As a result the arterial blood pressure and the flow of blood to the heart muscle diminish. This result in the weakening of the heart, further diminishes the pumping and coronary blood flow, and stills more weakness of the heart. The cycle repeats itself again and again until death.
Negative feedback system
a. Definition If some factor becomes excessive or too little, a control system, which consists of a series of changes that return the factor toward a certain mean value, thus maintaining homeostasis, called negative feedback system.
i. If the concentration of carbon dioxide in the extracellular fluid increases the pulmonary ventilation also increases. This inturn causes decreased CO concentration.
ii. Conversely, if the CO concentration falls to low, this causes a feedback increase in the concentration. Essentially all control system of the body operates by negative feed hack system.