The Urinary System – Concentration and Dilution

Last time, we talked about how the urinary system allows for our bodies to selectively reabsorbs things that were filtered out of our circulatory system. One of the molecules that can be reabsorbed is water, which is an important molecule for several reasons. In terms of the urinary system, water is important for the concentration and dilution of our urine.

The concentration and the dilution of urine is regulated by 2 hormones: Anti-diuretic hormone and Aldosterone.

The anti-diuretic hormone is released if you’re dehydrated, and literally translates to “against the passing of urine”. In situations where you are dehydrated, your blood volume will be low due to the lack of a sufficient amount of water, resulting in a lower blood pressure. To counteract this, the anti-diuretic acts to reduce the amount of water lost by the body and minimizes how much urine you make and release. This will result in a more concentrated urine that has a less water than usual and is a deeper yellow due to the higher concentration of urea.

Aldosterone is also released when you’re dehydrated. This hormone is responsible for the increase in thirst while also helping your body retain water by increasing the amount of sodium in your body. The more solute there is in your body, the more likely water is to stay with the solute (rules of osmosis, hurray!).

These hormones exert their effects primarily on the distal tubule of the nephron (after the loop of Henle), so that is where the water is reabsorbed!

So when these hormones are released, your urine will be more concentrated because water is retained by your body! Amazing, right?

Next week: We will finally get to talking about the effect of Alcohol on Urine!

Is there something you’d like to learn about? Tell me about it here and I may just do a post about it 🙂