Tutoring biology 12, you cover kidney function.  The biology tutor introduces ADH, which is a hormone used to regulate urine volume.

For explanation of how a kidney works, see my post here.

Today, we focus on the fine tuning of urine volume. The hypothalamus monitors the concentration of the blood. It may decide, for instance, that the blood risks dehydration. How can the hypothalamus respond to help prevent dehydration?

The hypothalamus has the option of ordering the posterior pituitary to release ADH (anti diuretic hormone). ADH acts on the cells of the distal convoluted tubule and the collecting duct, causing them to be more permeable to water. The result is that more water will be reabsorbed back into the blood. Subsequently, blood volume will stay higher, while urine volume will decrease.

Let’s imagine the other situation: the person has just drunk lots of water to flush themselves out. In such a case, the hypothalamus will detect the surplus of water in the blood, so won’t order the secretion of ADH. The cells of the distal convoluted tubule and collecting duct will allow less water to be recollected, so more will be left in the urine. Urine volume will increase, while blood volume will decrease.

At night, the hypothalamus may order the secretion of ADH to keep urine acculumation low during sleep. The benefit: the person will not have to get up as often to urinate – or maybe not at all until morning.

Another hormone – aldosterone – can also be used to influence urine volume. It will be discussed in a future post:)

Source: Biology 12, Module 4, Open School BC, 2007.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.