The Effect of Alcohol on Renal Collecting Tubule Permeability

Why do you feel like you need to pee so much when you drink alcohol? Well, part of the answer is that you're consuming more liquid than usual, so of course there's going to be more coming out of the other end. But there's more to it than that. I'll go ahead and give a short, simple answer, and then you can read in detail if you want.

In short: Alcohol inhibits the release of a hormone that usually keeps water in the body. So when alcohol is present, water basically just goes straight through you.

Let's start in the brain. The hypothalamus is a very important brain structure with a multitude of different functions in the human body. The function important in this discussion is its role in stimulating the pituitary gland, particularly the posterior pituitary in this case. In the posterior pituitary gland are two main hormones: vasopressin, aka anti-diuretic hormone (ADH), and oxytocin. Normally, the hypothalamus stimulates the pituitary to release vasopressin, which then plays a major role in the kidneys among other things. When you ingest alcohol, however, it interacts with the hypothalamus, resulting in an inhibition of the hormone and ultimately less ADH in the kidneys.

Here's a simple picture of the hypothalamic-pituitary system:



Now we'll move on to what usually happens in the kidney (well, just what's important anyway, there's a lot more to it than this and I don't feel like writing a book!). The kidney is composed of many structures called nephrons. There are about 1 million of these in each kidney! When plasma enters into the kidney, it is filtered in the glomerulus, which is basically just some specialized capillaries. The constituents of the filtered fluid are then either reabsorbed into the bloodstream, or pass through the nephron and into the bladder, where it is eventually excreted. Normally, most of the water that passes through the nephron is eventually reabsorbed. Some of this water is absorbed in the collecting tubule of the nephron, which you can see pictured below. When vasopressin is present, the hormone increases the permeability of these tubules, and thus water is readily absorbed back into the blood. In the absence of vasopressin, the tubules are less permeable, so water isn't as easily absorbed and instead goes into the ureters and then the bladder.



We'll put it all together now. Alcohol interacts with the hypothalamus, inhibiting the release of vasopressin (ADH) from the posterior pituitary gland. As a result, the collecting tubules in the kidney are less permeable to water, so the liquid will be more likely to pass through the nephron, into the bladder, making you have to pee more than usual. It's as simple as that!