Sunday, October 10, 2010
The renin-angiotensin system (RAS) or the renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and water (fluid) balance.
When blood volume is low, the kidneys secrete renin. Renin stimulates the production of angiotensin. Angiotensin causes blood vessels to constrict, resulting in increased blood pressure. Angiotensin also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the tubules of the kidneys to increase the reabsorption of sodium and water into the blood. This increases the volume of fluid in the body, which also increases blood pressure.
Among other things, angiotensin has a variety of effects on the body including the release of anti-diuretic hormone (ADH), also called vasopressin -- ADH is made in the hypothalamus and released from the posterior pituitary gland. As its name suggests, it also exhibits vaso-constrictive properties, but its main course of action is to stimulate reabsorption of water in the kidneys. ADH also acts on the central nervous system to increase an individual's appetite for salt, and to stimulate the sensation of thirst.
The above description is only the barest sketch. The complex chemical steps which control the fluid balance in our bodies and make life possible are beyond comprehension. To us, it appears that if "we don't drink enough, we get thirsty" however in fact there is an immense network of divinely designed chemical engineering working in the background which scientists are only now beginning to reveal to us. The next time we feel that need to drink, we have so much to thank God for.
Posted by jewish philosopher at 11:06 AM