Hormones and the excretory system
The function of the kidneys:
- Remove waste from the body
- A form of homeostasis which controls the volume of water in the body.
How the kidney works:
- Blood enters kidney via the The renal artery carries blood to the kidneys..
- Liquid and many dissolved substances are filtered out in the The outer layer of the kidney between the renal medulla and renal capsule..
- In the The inner part of the kidney., 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 The tube leading from the kidney to the bladder..
- Urine is stored in the The organ that collects urine as it is produced by the kidneys, and releases it when a mammal urinates..
- Urine is passed out via the Tube leading from the bladder to the outside of the body..
ADH 鈥 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 鈥 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 The waste product secreted by the kidneys. and returns blood water levels to normal.