Water Excretion Regulation

The brain and kidneys regulate the amount of water excreted by the body. When the blood volume is low, the concentration of solutes in the blood is high. The brain responds to this situation by stimulating the pituitary gland to release an antidiuretic hormone (ADH), which signals the kidneys to re-absorb and recirculate water. When the individual needs more water, the kidneys will excrete less and even reabsorb some.

pituitary gland: gland at the base of the brain that regulates multiple body processes hormone: molecules produced by one set of cells that influence the function of another set of cells blood pressure: measure of the pressure exerted by the blood against the walls of the blood vessels enzyme: protein responsible for carrying out reactions in a cell

When excessive fluid loss occurs, the blood volume will fall, as will blood pressure. The kidneys respond by secreting an enzyme called rennin. Rennin activates the blood protein angiotensinogen to convert to angiotensin, which causes the blood vessels to constrict and blood pressure to rise. An-giotensin also activates the adrenal glands to release a hormone called aldos-terone. Aldosterone causes the kidneys to retain sodium and water. When the body needs water, less is excreted and more is retained.

edema: accumulation of fluid in the tissues

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