Homeostatic system in the body acts through selfregulating devices, which operate in a cyclic manner. This cycle includes four components:

1. Sensors or detectors, which recognize the deviation

2. Transmission of this message to a control center

3. Transmission of information from the control center to the effectors for correcting the deviation

Transmission of the message or information may be an electrical process in the form of impulses

through nerves or a chemical process mainly in the form of hormones through blood and body fluids

4. Effectors, which correct the deviation.


Homeostatic mechanism in the body is responsible for maintaining the normalcy of various body systems.

Whenever there is any change in behavioral pattern of any system, the effectors bring back the normalcy

either by inhibiting and reversing the change or by supporting and accelerating the change depending

upon requirement of the situation. This is achieved by means of feedback signals. Feedback is a process in which some proportion of the output signal of a system is fed (passed) back to the input. This is done more often intentionally in order to control the behavior pattern of the system. Whenever any change occurs, system receives and reacts to two types of feedback:

1. Negative feedback

2. Positive feedback.


Negative feedback is the one to which the system reacts in such a way as to arrest the change or reverse

the direction of change. After receiving a message, effectors send negative feedback signals back to the

system. Now, the system stabilizes its own function and makes an attempt to maintain homeostasis.

Many homeostatic mechanisms in the body function through negative feedback. For example, thyroid-stimulating hormone (TSH) released from pituitary gland stimulates thyroid gland to secrete thyroxine. When thyroxine level increases in blood, it inhibits the secretion of TSH from pituitary so that, the secretion of thyroxin from thyroid gland decreases . On the other hand, if thyroxine secretion is less, its low blood level induces pituitary gland to release TSH. Now, TSH stimulates thyroid gland to secrete thyroxine.


Positive feedback is the one to which the system reacts in such a way as to increase the intensity of the change in the same direction. Positive feedback is less common than the negative feedback. However, it has its own significance particularly during emergency conditions. One of the positive feedbacks occurs during the blood clotting. Blood clotting is necessary to arrest bleeding during injury and it occurs in three stages.

The three stages are:

i. Formation of prothrombin activator

ii. Conversion of prothrombin into thrombin

iii. Conversion of fibrinogen into fibrin.

Thrombin formed in the second stage stimulates the formation of more prothrombin activator in addition

to converting fibrinogen into fibrin. It causes formation of more and more amount of prothrombin

activator so that the blood clotting process is accelerated and blood loss is prevented quickly. Other

processes where positive feedback occurs are milk ejection reflex and parturition and both the processes involve oxytocin secretion.

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