Hormones and the excretory system

The function of the kidneys:

Excretory sytem

How the kidney works:

  • Blood enters kidney via the renal artery.
  • Liquid and many dissolved substances are filtered out in the cortex.
  • In the medulla, water and some of the substances are reabsorbed back into the blood in a controlled way until normal concentrations are reached.
  • Any water and dissolved substances left over pass into the urine, which collects in the renal pelvis.
  • Urine passes into the ureter.
  • Urine is stored in the bladder.
  • Urine is passed out via the urethra.

ADH – anti-diuretic hormone

The reabsorption of water back into the blood (at the medulla) is controlled by the anti-diuretic hormone (ADH).

ADH is produced by the part of the brain that monitors water levels in the blood.

It is then carried in the blood to its target organ – the kidneys.

When the brain detects lower than normal water levels in the blood, ADH is produced. In the medulla, ADH causes more water to be reabsorbed from the urine back into the blood. This produces a lower volume of more concentrated urine and returns blood water levels to normal.

When the brain detects higher than normal water levels in the blood (e.g. from drinking more than normal), less or no ADH is produced.

In the medulla, less water is reabsorbed back into the blood.

This produces a larger volume of dilute urine and returns blood water levels to normal.

Hormones ADH