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Anonymous users2024-02-11No, skin color is related to ultraviolet rays, just go out and rub some sunscreen.
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Anonymous users2024-02-10The constant body temperature of the human body is an important factor to ensure the stability of the internal environment of the body. The maintenance of normal body temperature is the result of the dynamic balance of the body's two processes: heat production and heat dissipation. The human body maintains a body temperature of around 37 on a regular basis through a precise thermoregulation mechanism.
Among them, the body temperature regulation effect of ** is mainly manifested in heat dissipation. Heat dissipation accounts for 90% of the total heat dissipation (1) Vascular neuropathic thermoregulation: This regulation is controlled by the thermoregulatory center, that is, the heat dissipation or thermogenesis center of the hypothalamus, the sympathetic nerve center of the medulla oblongata, and the spinal cord center.
When there is a change in body temperature and external temperature, the afferent information emitted by the peripheral cold and hot thermoreceptors and deep thermoreceptors on ** is integrated with the high and low regulatory centers of body temperature regulation (hypothalamic thermoregulatory center, bulbar and spinal cord center), and then the efferent impulse is issued by the center to the effector organs, and the sympathetic nervous system controls the tensile activity of ** blood vessels, and finely regulates the superficial blood flow to increase or decrease the heat emitted by the body surface. (2) Heat dissipation regulation: There are four physical mechanisms of heat dissipation, namely radiation, convection, conduction and evaporation.
Radiation: Moving in a straight line from the surface to the surroundings in the form of electromagnetic waves and at the speed of light. Under standard conditions, that is, when the temperature is 25, radiant heat dissipation accounts for about 60% of the total heat dissipation.
When the temperature between ** and the environment is larger, or the effective radiation area of the body is larger, the more radiation heat dissipation. Convection: The change in the flow of air due to heat is called convection.
The body emits approximately 20% of the total heat loss by convection under standard conditions. When the ambient air temperature is low or the air moves fast, the convection heat dissipation effect is also enhanced. Conduction:
The process by which heat moves from one object to another through contact is called conduction. The heat in the deep part of the body moves to the surface of the body in a conductive manner, and then directly conducts it to the objects that come into contact with it. Since it is a poor conductor of heat, conduction is of little significance in heat dissipation.
Evaporation: In addition to the evaporation of respiration, evaporation heat dissipation is at standard temperature, accounting for about 26% of the total heat dissipation. When the outside temperature is equal to or exceeds the ** temperature, radiation, conduction, and convection all stop working, and evaporation becomes the only way to dissipate heat.
Evaporation is divided into two ways: insensible sweating and overt sweating. The former actually has nothing to do with sweating, even when the human body is in low temperature conditions and there is no sweat secretion, ** and the respiratory tract still have water that continues to seep out and evaporate. The latter is overt sweating, and evaporating ml sweat can dissipate heat.
Water needs heat when it turns into steam, so when the surface water evaporates, it cools.
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