Let's suppose that you drink a lot of water quickly. The water is absorbed from your gut into the bloodstream, and it has the effect of diluting the blood. The diluted blood reaches the kidney,which takes excess water out of it and passes it into the urine.
Salt is dealt with in the same way. If you had a salty meal the salt is absorbed into your blood. When the salty blood reaches thekidney the salt is removed from it and passed into the urine. Thisis an extremely important function of the kidney.
The relative amount of water and salt in the blood give the blood a particular concentration.By regulating the amount of salt and water in the blood, the kidneys ensure that the concentration and volume of theblood stays more or less the same all the time.
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Another crucial function of the kidney is to regulate blood-pressure .
They secrete an enzyme called renin, which activates hormonal mechanisms that controls blood pressure and electrolyte balance. When, for instance, blood-pressure begins to fall, the kidneys release the enzyme renin . This enzyme converts blood protein into a hormone called angiotensin .
Angiotensin then induces the adrenal gland to release another hormone called aldosterone . This hormone causes sodium and water to be reabsorbed intothe blood, thereby increasing blood-volume and blood-pressure. The response of the kidneys to aldosterone helps to regulate the level of salt in the blood.
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The kidney also regulates the body's pH balance ... by adjusting the body's acid-base balance. If the blood is too acidic, meaning that there is anexcess of hydrogen ions, the kidney moves these ions to theurine.
Bacteria (which cause many serious degenerative diseases) flourish in an acidic environment. The kidneys help to maintain the blood plasma at a neutral pH 7.4. By regulating the body's pH, the kidneys help to maintain an environment which prevents diseases and promotes the efficient functioning of all bio-systems within the body.