Preksha Dhyana Human Body Part 2

Author(s): Jethalal S Zaveri
Publisher: Jain Vishva Bharati

Page 53

continual adjustments both of intake-through the thirst mechanism and of output-mainly by variation of urine formation.
Input
The mechanism of thirst is apparently simple, but actually rather complex and not entirely understood. A drying of mucous membrane of the mouth and a cessation of saliva flow play an important role in the immediate sensation of thirst and serve as a stimulus to fluid intake. But these sensations are controlled by the thirst centre in the hypothalamus. When the extracellular fluids are too concentrated, impulses from the control centre somehow give rise to the sensation of thirst. The feedback system is tuned to conditions of excess loss of fluid. For example, hot weather or participation in sports or other strenuous exercises force us to drink frequently, because fluid pours out by the sweat glands as the body works to dissipate the excess heat. The moistening of the mouth and the distension of the stomach, resulting from the act of drinking, initiate feedback impulses which turn off the stimulation of the thirst centre. When large quantities of fluids are taken in, water is rapidly absorbed from the intestinal tract into the plasma compartment. Both the blood volume and cardiac output may be temporarily increased. But soon the fluid passes into the interstitial compartment and the kidneys step up their elimination of water. Balance is rapidly restored. Thus within the body there is a continual interchange of water and other materials among the compartments. Interstitial fluid plays an important role in the body's fluid dynamics.
Output
We have an efficient system of sweat glands to lose heat through evaporation of water. Even on a cool day, we continually lose water through the skin. This mechanism is an important part of the body's temperature-control-system but maybe a threat to the body's fluid-balance, if intake is limited. Under normal condition the fluid-loss through