Geoff G. answered • 03/14/22
Current A&P Instructor with Extensive Physiology Experience
You can get some insight into the function of ADH by looking at its name - anti-diuretic hormone. A diuretic is something that causes you to urinate. Alcohol and caffeine are examples.
The function of ADH is to help retain water if the body is becoming dehydrated. If the body senses that water levels are too low, ADH will be released from the posterior pituitary. It causes the epithelial cells lining the collecting duct of the kidney to create protein channels called aquaporins which embed themselves in the cells' plasma membrane. This allows water to leave the duct and enter the interstitial fluid of the renal medulla before entering the bloodstream.
Therefore ADH lowers the amount of water in your urine and it's a negative feedback mechanism because it helps raise the amount of water in the body when it's getting too low. Remember that when a level or quantity of something moves towards an unsafe extreme, negative feedback mechanisms reverse that trend to move the quantity towards the middle of a safe homeostatic range. This is true whether the level is trending towards either the high or low end of the safe range.
As a side note, an interesting demonstration of how ADH works comes from the effects of drinking alcohol. If you're of legal drinking age you may have experienced a situation in which your urination is frequent and clear when you've been drinking. This is because alcohol interferes with the release of ADH.
