Mechanism Of Action Of Homeostatic System

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Chapter: Anatomy, Physiology And Health Education : Homeostasis

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.


MECHANISM OF ACTION OF HOMEOSTATIC SYSTEM

 

 

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 FEED BACK

 

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 (Fig. 4.2). 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 (Refer Chapter 67 for details). Another example for negative feedback mechanism is maintenance of water balance in the body.

 

 

POSITIVE FEEDBACK

 

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:

 

a.                    Formation of prothrombin activator

b.                    Conversion of prothrombin into thrombin

c.                    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 (Fig. 4.4). 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 (Fig. 4.5) and both the processes involve oxytocin secretion.

 

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