HORMONES THAT INFLUENCE REABSORPTION OF WATER
Aldosterone is secreted by
the adrenal cortex in re-sponse to a high blood potassium level, to a low blood
sodium level, or to a decrease in blood pressure. When aldosterone stimulates
the reabsorption of Na+ ions, water follows from the filtrate back
to the blood. This helps maintain normal blood volume and blood pres-sure.
You may recall
that the antagonist to aldosterone is atrial
natriuretic peptide (ANP), which is secreted by the atria of the heart when the atrial walls are stretched by
high blood pressure or greater blood vol-ume. ANP decreases the reabsorption of
Na+ ions by the kidneys; these remain in the filtrate, as does
water, and are excreted. By increasing the elimination of sodium and water, ANP
lowers blood volume and blood pressure.
Antidiuretic hormone (ADH) is
released by the posterior pituitary
gland when the amount of water in the body decreases. Under the influence of
ADH, the distal convoluted tubules and collecting tubules are able to reabsorb
more water from the renal filtrate. This helps maintain normal blood volume and
blood pressure, and also permits the kidneys to produce urine that is more
concentrated than body fluids. Producing a concentrated urine is essential to
prevent excessive water loss while still excreting all the sub-stances that
must be eliminated.
If the amount
of water in the body increases, how-ever, the secretion of ADH diminishes, and
the kid-neys will reabsorb less water. Urine then becomes dilute, and water is
eliminated until its concentration in the body returns to normal. This may
occur follow-ing ingestion of excessive quantities of fluids.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.