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Antidiuretic hormone
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Antidiuretic hormone, also called vasopressin, is the hormone that decides how much water the body holds on to. It is made by neurons in the hypothalamus, a small region at the base of the brain, and it travels inside the extensions of those neurons to the posterior pituitary, the gland that releases it into the blood.
It acts in the kidney, in the last part of the tubule and in the collecting duct, the structures that carry urine as it is being formed. When the hormone arrives, it makes the wall of those ducts produce water transport proteins, and water goes back into the blood through them instead of leaving in the urine. It is like installing floodgates in the tubule wall, and water returns to the blood through them.
What sets all of this off is how concentrated the blood is. The neurons that make the hormone carry osmoreceptors, sensors that measure how concentrated the blood is, and they are so finely tuned that they react to a change of two milliosmoles per liter, a tiny difference.
In brief
Antidiuretic hormone, also called vasopressin, is a nonapeptide synthesized in the hypothalamus and released from the posterior pituitary.
When present it drives expression of water transport proteins in the late distal tubule and collecting duct, increasing water reabsorption.
It is like installing floodgates in the tubule wall, and water returns to the blood through them.
Its neurons carry osmoreceptors so sensitive that they respond to changes of two milliosmoles per liter in blood osmolarity.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Vasopressin, StatPearlsPublished
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