Question

Why would drinking 4 beers over the course of a night cause you to urinate more often but still feel dehydrated? (Describe the glomular filtration, tubular reabsorption, and tubular secretion involved in this)

Answer 1

First, your kidneys regulate the amount of water in your body. They do this by monitoring the plasma osmolality of your blood.

Osmolality is a fancy word to describe the ratio of particles in your blood to fluid. If you have more fluid than particles, your kidneys tell your body to release more urine.

When you have more particles than fluid, your kidneys hold on to fluid, and you don’t feel the need to pee.

Because alcohol is a liquid, it tips the osmolality in favor of more fluid. As a result, you’ll ultimately pee out the equivalent of what you drink (assuming your kidneys are working well).

Drinking alcohol inhibits the body’s release of the hormone vasopressin. Doctors also call vasopressin anti-diuretic hormone (ADH).

Typically, the brain signals the release of ADH in response to an increase in particles over fluids (plasma osmolality). The ADH signals your kidneys to hold on to water.

By suppressing ADH, alcohol can make the kidneys release more water. This can have a dehydrating effect on your body that not only makes you pee more, but can also cause headaches and nausea later.