There are as many as millions of creatures on the earth, and humans are one of them. An interesting phenomenon is that humans are the only species that need clothing to keep warm in winter.
Also facing the cold winter, why are only humans need to wear clothes? Because as mammals, humans have taken the initiative to shed their hair on their bodies during the long evolution process, and they have no cover, so of course they need to wear clothes. Other mammals have thick fur to resist the severe cold.
So, why do humans have to lose their hair all over their bodies? The main function of hair is to resist severe cold, but its disadvantage is also obvious, that is, it affects heat dissipation. When the weather is hot, animals are prone to sweating, but due to the existence of hair all over the body, the heat in the body cannot be dissipated, and they will be killed by heat over time. This may be the reason why humans lose all their hair.
Like other mammals and birds, humans are also constant temperature animals and can maintain relatively stable body temperature under changes in ambient temperature.
The principle of constant temperature in animals is not complicated. It mainly produces stable body temperature through metabolism of . The basal metabolic rate of constant temperature animals is much higher than that of variable temperature animals. Their body temperature regulation system can ensure the constant body temperature and can discharge heat when the temperature of the external ambient increases. This process is mainly achieved through the evaporation of liquids, such as humans sweating when the weather is hot.
The benefits of constant body temperature are obvious. Constant body temperature can keep animals alive in a very cold environment. Although warming animals can survive without changing their body temperature in cold environments, their activity volume is significantly reduced or even stopped. For example, snake must enter dormant state in winter, while mammals represented by humans can maintain normal activities in cold environments.
Human body temperature is generally maintained at 37℃. When the external temperature is too low, humans will increase heat by burning fat in their bodies to maintain constant body temperature; when the external temperature is too high, humans will release heat by sweating and other means, so that the body temperature will drop to a constant temperature of 37℃.
However, humans have limited ability to regulate body temperature. When the external temperature is too low, it will cause humans to fail in temperature control, and their body temperature drops rapidly until they are frozen to death.
In the cold and cold winter in Russia, 42,000 people are frozen to death outdoors every year. Most of them walk out of the outdoors while drinking too much vodka . A considerable number of these people who have been frozen to death will make some strange actions before being frozen to death, such as taking the initiative to take off their clothes and smiling. Why does this happen?
Humans regulate their body temperature through the brain. When the temperature outside decreases, our skin first senses this and then reports information about the temperature drop to the brain. After the brain obtains this information, it will immediately issue instructions to the body to increase heat and maintain body temperature through some actions. For example, some people will shake their bodies when they feel cold or get goose bumps. Such actions are actually consuming the body's fat to maintain body temperature.
If humans are in a low temperature state for a long time, central nervous system will not be able to operate normally, which will also lead to vasodilation. Vascular dilation causes warmer blood in the heart and its surroundings to flow to the cold limbs. At this time, humans will feel that their bodies are hot, which is actually an illusion.
However, the body will still pass this illusion to the brain. After the brain receives the message that "body is hot", it is possible to make an instruction to "take off clothes". Therefore, some people will only make abnormal actions such as taking off their clothes before they are frozen to death. And once this reaches this point, this person is not far from death.
In fact, when humans are frozen to death, their body temperature gradually decreases. When the temperature of the human body drops to 36℃, the central nervous system will become excited, and the human body will begin to experience rapid heartbeat and shortness of breath.When the temperature of the human body drops to 33℃, the human body will become slow to react, reduce metabolic levels, become dizzy in mind, and gradually become unconscious.
When the temperature of the human body drops to 20℃, the body basically stiffens, almost all perception ability is lost, all the functions of the body are basically in a stagnant state, the pulse of the heart is beating very little, and it has reached a state of dying.
Before humans are frozen to death, because they feel their bodies are very warm, some people will unconsciously show a satisfied smile, then close their eyes and will never open them again.
It should be pointed out that not all people who have been frozen to death will take off their clothes and smile, and the probability of this situation is about one-quarter.
Low temperature is a great harm to humans. It can not only cause body damage such as freezing and frostbite, but also cause some diseases through indirect means, which is harmful to the elderly, pregnant women and fetus. This also explains why human mortality rates are higher in winter, especially for the sick elderly, whether they can survive a long winter is a big test.
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