Antidiuretic Hormones

We will group here under the term antidiuretic hormones the two main hormones that can reduce the production of urine in the human kidneys. The first one is vasopressin, also named ADH (AntiDiuretic Hormone) and the second is aldosterone.

They have obvious medical importance due to the prominence of their role in body water regulation.

Vasopressin (ADH)

ADH is a peptidic hormone produced in the hypothalamus that acts directly upon the kidneys. Upon a higher than normal osmolarity of the bloodstream (a higher than usual concentration of ions and metabolites), ADH is released from neurons and upon reaching the renal nephrons, acts upon the distal tubule to trigger a higher rate of water reabsorption. The additional water retained back in the bloodstream dilutes the metabolites and bring the osmolarity down to normal level, maintaining the homeostasis. The obvious side effect is a reduced output of urine volume, thus an anti-diuretic effect.

Aldosterone

Aldosterone is also a hormone, this time produced in the adrenal gland topping the kidney, that acts upon the distal tubules in the nephron. Subnormal blood pressure or an increase in potassium concentration in the plasma, among others, triggers the production and secretion of aldosterone. Aldosterone will, in turn, stimulates the transmembrane Na⁺/K⁺ pumps of the cells lining up the renal distal tubules, inducing the reabsorption of Na⁺ (and thus water) and the excretion of K⁺. The reabsorption of Na⁺ sodium potassium pumps of the cells lining up the renal distal tubules, inducing the reabsorption of sodium (and thus water) and the excretion of potassium. The reabsorption of sodium and water results in a higher blood volume, and thus a higher blood pressure as well as a decrease of plasma potassium concentration to normal levels.

Aldosterone also regulates several other processes in the guts, saliva and sweat glands regarding K⁺ potassium secretion.