Outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt levels in the blood
Water Balance and Blood Pressure • Water levels in the body are closely associated with blood pressure. • Increased water increases blood pressure • Dehydration decreases blood pressure • Involves ADH and aldosterone
ADH – anti-diuretic hormone • Also called vasopressin • Produced in the brain in the hypothalamus • Osmoreceptors (detect water levels in the body) activate neurosecretary cells in the hypothalamus in response to increased blood solutes (less water) • Vasopressin travels to the pituitary gland and is released into the blood stream. • ADH acts in the kidneys increasing the permeability of the distal tubules to water. Water reabsorption increases.
Osmoreceptors also make you feel thirsty. • Increased drinking and increased reabsorption of water decrease the concentration of solutes in the blood. • This acts as negative feedback and stops the production of ADH (vasopressin)
Aldosterone • When water levels in the blood decrease, blood volume and blood pressure decrease. A decrease in blood pressure changes the glomerular filtration rate. • In response to low blood pressure renin is secreted in the kidneys. • Renin triggers the adrenal cortex (outside edge of the adrenal gland) to release aldosterone. • Aldosterone increases reabsorption of sodium in the distal tubule which increases reabsorption of water. Increased water leads to increased blood pressure.
Aldosterone and ADH (vasopressin) work together to effectively maintain water concentration in the blood and tissues and blood pressure. • Patients with Addison’s Disease (inability of the adrenal gland to secrete sufficient hormone) do not produce aldosterone. The body is unable to control the amounts of sodium and potassium. This can lead to heart failure within a few days. Hormone injections can be given at physiological levels. This is called aldosterone replacement therapy. Drinking a salt solution is suitable if insufficient aldosterone is produced.