Hormones that act on the kidneys

ADH (Antidiuretic Hormone)

The brain and kidneys regulate the amount of water excreted by the body. When the blood volume is low, the concentration of solutes in the blood is high. When the hypothalamus senses this low blood volume and increased serum osmolality it synthesizes ADH, a small peptide molecule. The pituitary gland then releases ADH into the bloodstream and causes the kidneys to retain water by concentrating the urine and reducing urine volume. Water retention boosts blood volume and decreases serum osmolality.

Animation: Decreased blood volume stimulates the release of ADH


ADH (continued)

Increased blood volume prevents the release of ADH. As a result, the kidneys retain less water, which dilutes the urine and increases urine output. As fluid leaves the body, blood volume decreases and serum osmolality increases. This stimulates the release of ADH and the cycle begins anew.

Animation: Increased blood volume prevents the release of ADH



Renin-Angiotensin-Aldosterone System

It is important for the body to keep sodium and water balances in check, and also to maintain healthy blood volume and blood pressure. The renin-angiotensin-aldosterone system assists with this in the following manner:

  1. The glomulerus, a bundle of capillary blood vessels found in the kidney, senses a drop in blood flow or sodium and secretes an enzyme called renin into the bloodstream.
  2. Renin moves to the liver where it converts the inactive peptide angiotensinogen to angiotensin I.
  3. Angiotensin I travels to the lungs where another enzyme converts it to angiotensin II.
  4. Angiotensin II makes its way to the adrenal glands at the top of the kidneys where it stimulates the production of aldosterone.
  5. Aldosterone helps the kidneys conserve sodium and water, leading to increased fluid volume and sodium levels.

NOTE: If blood flow to the kidneys or the amount of sodium increases, less renin is produced in an attempt to normalize blood pressue.

Animation: Decreased blood volume or blood pressure stimulates the release of Renin



Atrial Natiuretic Peptide

When blood volume and blood pressure increase, the stretched atria release Atrial Natiuretic Peptide (ANP), a cardiac hormone. ANP promotes natriurisis by shutting down the renin-angiotensin-aldosterone system and causing vasodilation. As the blood vessels expand, urine excretion of sodium and water increases, stabilizing blood volume and blood pressure.

Animation: Increased blood volume or blood pressure stimulates the release of ANP