3.6: Outline the role of hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt levels in blood.
by Janelle Mansour
1. The two hormones which bring about changes in permeability are: ALDOSTERONE (brings about retention of salts), and ADH (brings about water reabsorption).
2. ADH: made in the hypothalamus, but stored and released from the pituitary gland. When there is a low concentration of water, the hypothalamus detects the drop in the blood volume, which then stimulates the secretion of ADH. ADH increases the permeability of the distal tubules and the collecting ducts to water. As the collecting ducts run through the highly concentrated medulla of the kidney, more water is reabsorbed into the kidney tissue and bloodstream so that water is conserved within the body.
2.1. New node
3. These changes in permeability are brought about by hormones. Hormones are chemical control substances that are secreted by the endocrine glands directly into the blood stream.
4. Adjustments to the concentration of water and salts within the urine takes place mainly in the DISTAL parts of the tubules and he COLLECTING TUBULES, by alterations to the permeability of the membranes of the cells lining the nephron walls.
5. ALDOSTERONE: When there is a low concentration of sodium ions, blood volume and blood pressure is reduced. This stimulates the secretion of the hormone aldosterone. When it reaches the kidney, it increases the permeability of the nephron to sodium, particularly in the ascending limb of the loop of Henle. reabsorption then occurs, hereby resulting in the retention of salts in the body, and furthermore, less concentrated urine.
6. Both ADH and ALDOSTERONE therefore play an important role in helping the kidney to carry out its homeostatic functions of osmoregulation: - REGULATION OF THE SOLUTE CONCENTRATION OF THE BLOOD. -REGULATION OF BLOOD VOLUME.
