Is frequent urination really because you don't sweat?

Is it because you don't sweat that you have too much urine in cold weather?

As the saying goes, "cold urine and hot fart" refers to the phenomenon that people tend to fart more in hot weather and urinate more often in cold weather.

Especially, no matter what the original temperature is, as long as the cold wave comes and the temperature drops suddenly, there will be more urine and even frequent urination.

Why is it cold to urinate too much?

One of the most popular explanations is that people who are afraid of cold do not sweat, and urine will naturally increase only if the water in the body is excreted through urine.

This explanation seems reasonable. Complex physiological problems can be "solved" by the simplest principle of addition and subtraction.

Unfortunately, however, this "intuitive" explanation is not correct.

So, what is the real reason for cold weather and excessive urine?

The answer is not simple, involving at least three physiological mechanisms.

As we know, people are "warm-blooded animals" and are extremely sensitive to environmental temperature changes. Even a slight temperature change will be adjusted in time to maintain the stability of the core body temperature needed for life activities.

Under the general environmental temperature of human life, the maintenance of heat balance is mainly to adjust the blood flow of skin through the contraction and relaxation of skin blood vessels, and to adjust the heat loss by changing the temperature difference between skin and environment.

The temperature sensor distribute on that skin is extremely sensitive to the ambient temperature. As long as the temperature drops below 17, exposed skin will feel cold and skin blood vessels will contract to the maximum extent, which is also the physiological mechanism that long-term exposure below 17 will lead to frostbite (frostbite usually occurs in late autumn and early winter, not winter).

Adult skin area is as high as 2 square meters, which is the largest organ of human body, and the circulating blood volume is very considerable and changes greatly.

At a suitable temperature, the whole body skin blood flow is about 250 ml/min.

Under the high temperature in summer, the maximum can reach 6~8 liters/minute.

When the temperature drops below 17, it can be as low as 20-50 ml/min, assuming the whole body is naked.

In this way, as long as the temperature drops in cold days, the blood circulation around the skin will be significantly reduced.

Where's the blood in the skin?

Being "squeezed" into the deep blood vessels of the body by cold is medically called "central circulation"; Accordingly, that blood circulation of the skin is cal "peripheral circulation".

In cold weather, especially when the temperature drops suddenly, the contraction of skin blood vessels will "expel" more blood to the central circulation.

The volume of central circulation is relatively constant, and a sudden increase in a large amount of blood will lead to an increase in blood pressure.

The increase of blood volume and blood pressure will stimulate the related volume and baroreceptor, and send a signal to inhibit the hypothalamus from producing antidiuretic hormone.

We know that antidiuretic hormone is the main hormone to regulate urine, and its increased secretion will act on renal tubules, reduce urine production and retain body fluids.

When people don't drink water for a long time, or sweat and diarrhea lead to dehydration, it will stimulate the increase of antidiuretic hormone and reduce urine output.

On the contrary, inhibiting the secretion of antidiuretic hormone in cold weather will increase the production of urine, which is manifested as polyuria.

Of course, no matter what the temperature is, as long as there is no sudden drop, the human body has established a new homeostasis in this environment, and urine will not increase significantly.

Therefore, it is not accurate to say that it is cold and urine is more; It should be said that rapid cooling will lead to polyuria.

Cold causes polyuria, not only through the action of antidiuretic hormone, but also directly stimulates the receptors on the skin, leading to the decrease of bladder capacity, which is also commonly known as "small urinary vesicle".

Therefore, cold can not only increase urine volume absolutely, but also reduce bladder capacity, causing frequent urination; In turn, frequent urination will produce more urine.

Of course, this kind of stimulation requires a lower temperature, so in the winter cold wave, the frequency of urination is more obvious.

Not only the sudden drop of ambient temperature will cause frequent urination, but also local contact with low-temperature objects will directly induce frequent urination and even urgency.

For example, washing your hands with cold water in cold weather and stepping barefoot on the cold ground will aggravate the feeling of frequent urination.

This is because the "cold" temperature sensor on the skin can directly send a signal to cause excessive activity of bladder detrusor, thus inducing frequent urination and urgency.

Cold weather without sweating is not the cause of polyuria.

On the contrary, people intuitively think that cold weather without sweating is not the cause of polyuria.

There is a simple reason. It's not just that it's cold and you don't sweat.

Sweating is that the heat generated in the body is significantly higher than the heat lost through non-evaporation (sweating) of the skin, and the heat accumulates in the body, leading to an increase in the core body temperature.

At this point, the thermoregulatory center will start the rapid heat dissipation mechanism of sweating.

The heat dissipation efficiency of sweating is extremely high. If 1 g sweat evaporates completely on the skin, it can take away 56 kilocalories.

Under normal circumstances, when the human body is at rest, it does not generate excess heat through exercise. Only when the ambient temperature rises above 32℃, the temperature difference between the skin (average temperature is 32℃) and the environment drops to 0, and the heat dissipation channel other than evaporation fails, will the fast channel of sweating be started and the heat dissipation be accelerated.

The temperature above 32 is unusually high, which is not the temperature of people's usual living environment.

Sweating is not a normal way to dissipate heat, so not sweating in cold weather will not have any "contribution" to urine.