What does ADH do in the Kidney?

ADH or Anti Diuretic Hormone is a hormone that regulates the amount of water absorbed in the kidney. It acts on the collecting duct of the kidney, which is the last part of the nephron (a single functional unit of the kidney). There are around 1 million nephrons in each kidney! Its role is to control the reabsorption of water. It does this by inserting more aquaporins into the membrane of the collecting duct. These aquaporins allow water to be reabsorbed into the capillaries. As a result the urine passed out increases in concentration (less water, same number of solutes) and hence ADH gets its name from this - Anti Diuretic (reducing urine production). ADH is also known as Vasopressin. When we are thirsty or our body does not have enough water, this is detected and more ADH is secreted so we try to retain as much water as we have. The opposite occurs, when we are well hydrated.