In hot weather, cooling off in the lake or outdoor pool is just what you need. But as soon as you swim in the water, the urine pressure increases and you suddenly have to go to the toilet urgently. But why? ntv.de explains the well-known phenomenon.
Summer is here, the bathing season has begun. Many people are drawn to outdoor pools or lakes. But as soon as you stay a little longer in the refreshing water, the urge to urinate increases - even though you haven't drunk much or have even been to the toilet shortly before. how come Is the water pressing on the bladder? Or did you swallow too much liquid while bathing?
The answer is simple and surprising: it has nothing to do with the water or the urine - it's the blood. Because the blood circulation in our body is adapted to land conditions, where gravity tends to cause more blood to collect in the legs. The buoyancy of the water means a change for the body. Without gravity, the blood can circulate more easily and is distributed more to the upper half of the body than usual. If you also swim, i.e. have your legs at the same level as your upper body, you allow even more blood to get into your torso and head.
The water pressure also acts like a compression stocking on the arms and legs and constricts the vessels in the limbs. This also allows the blood to flow more towards the middle of the body. The deeper you are in the water, the stronger the urge to urinate. According to experts, this phenomenon should be known to divers in particular.
"In this way, our body's control system is fooled into believing that we have too high a blood volume," says physician Claus-Martin Muth of the "Tagesspiegel". However, the large amount of blood in the middle of the body does not press on the bladder, but on the heart. Receptors, which are mainly located in the walls of the heart atria, constantly monitor the blood volume. "If they register too much blood, the kidneys are alerted to excrete fluid," explains the senior physician in anesthesiology at the University Hospital in Ulm.
The body's emergency strategy is therefore: relieve pressure. The kidney gets the signal to drain and promptly fills the bladder with urine. You have to go to the toilet, although there is actually not too much liquid in your body. The process is scientifically described with the Gauer-Henry reflex (or Henry-Gauer reflex), which the two researchers of the same name discovered in the 20th century.
The whole thing is reinforced by the mostly cool water, especially in lakes. If you stay there longer, the cold ensures that the body collects the blood in the middle of the body as much as possible to protect the vital organs. This pushes even more blood from the arms and legs into the vessels in the trunk.
Can you avoid the hassle of having to? According to experts, this is neither really possible nor sensible. "We're just land animals," says Jürgen Scharhag from the Heidelberg University Hospital of the "Schweriner Volkszeitung". Humans are not adapted to life in the water. According to the physician, the healthiest thing is to simply accept the deception of our control system. Then you quickly go to the toilet in between, and then take a relaxed bath again.
The control system is sometimes even capable of learning. According to Claus-Martin Muth, competitive swimmers, diving instructors or other people who spend a lot of time in the water every day tend to lose their urge to urinate. Your body adapts. "But if you take a three-week vacation and hardly go into the water during this time, everything is back to normal," says Muth.
By the way: Even when it's cold outside, for example in winter, the urge to urinate increases. A similar mechanism is at work here. Specialists call it "cold-induced diuresis". First, blood is drawn away from the skin and limbs so heat is not lost to the outside air. As in water, this means: more blood in the middle of the body. The kidneys then equalize the pressure. Time for a pee break.
(This article was first published on Saturday, June 25, 2022.)