The Control of Body Temperature | 体温的调控

📚 The Control of Body Temperature | 体温的调控

Body temperature is one of the most tightly regulated variables in the human body. In A-Level Biology, thermoregulation is used as a key example of homeostasis and negative feedback. Understanding how the hypothalamus, thermoreceptors, blood vessels, sweat glands and muscles work together helps to explain how mammals survive in changing environments.

体温是人体内调节最严密的变量之一。在 A-Level 生物课程中，体温调节是内稳态和负反馈的关键实例。理解下丘脑、温度感受器、血管、汗腺和肌肉如何协同工作，有助于解释哺乳动物如何在不断变化的环境中生存。

1. Homeostasis and Core Temperature | 内稳态与核心体温

Homeostasis is the maintenance of a relatively stable internal environment within narrow limits. Core body temperature in humans is kept at approximately 37 °C because this is the optimum temperature for enzyme activity and metabolic reactions. If the temperature deviates too far, enzyme structure can change and reaction rates fall.

内稳态是指将内环境维持在相对稳定且狭窄的范围内。人类核心体温保持在约 37 °C，因为这是酶活性和代谢反应的最适温度。如果温度偏离过大，酶的结构可能发生改变，反应速率随之下降。

Core temperature refers to the temperature of deep structures such as the heart, liver, brain and blood. It is monitored more closely than skin temperature because skin temperature can vary widely with the surrounding air, water or clothing. A stable core temperature is therefore a better indicator of the body’s true thermal state.

核心体温指心脏、肝脏、脑和血液等深层结构的温度。机体监测核心体温比监测皮肤温度更可靠，因为皮肤温度会随周围空气、水或衣物大幅变化。因此，稳定的核心体温更能反映身体真实的热状态。

2. Thermoreceptors and the Hypothalamus | 温度感受器与下丘脑

Thermoreceptors are sensory receptors that detect changes in temperature. Peripheral thermoreceptors are located in the skin and detect external temperature changes. Central thermoreceptors are located mainly in the hypothalamus and detect the temperature of the blood flowing through the brain.

温度感受器是检测温度变化的感觉受体。外周温度感受器位于皮肤，检测外部温度变化。中枢温度感受器主要位于下丘脑，检测流经大脑的血液温度。

The hypothalamus acts as the thermoregulatory centre. It receives nerve impulses from both peripheral and central thermoreceptors. The anterior hypothalamus contains heat-sensitive neurons that respond to rises in core temperature, while other regions respond to cooling. The hypothalamus compares the incoming information with a set point and then coordinates appropriate corrective responses.

下丘脑充当体温调节中枢。它接收来自外周和中枢温度感受器的神经冲动。下丘脑前部含有对核心温度升高敏感的热敏神经元，而其他区域对降温作出反应。下丘脑将传入信息与设定点进行比较，然后协调适当的纠正反应。

3. The Negative Feedback Loop | 负反馈回路

Thermoregulation is a classic example of negative feedback. When core temperature rises above the set point, the hypothalamus activates heat-loss mechanisms. When core temperature falls below the set point, it activates heat-gain or heat-conservation mechanisms.

体温调节是负反馈的典型例子。当核心体温升至设定点以上时，下丘脑启动散热机制。当核心体温降至设定点以下时，下丘脑启动产热或保温机制。

These responses bring the core temperature back towards the set point. As the temperature returns to normal, the stimulus decreases, and the corrective responses are reduced or switched off. This prevents overcorrection and keeps the internal environment stable.

这些反应使核心体温回到设定点附近。当体温恢复正常时，刺激减弱，纠正反应随之减少或停止。这可以防止过度纠正，保持内环境稳定。

Core temperature ≈ 37 °C | 核心体温约为 37 °C

4. Responses to Heat: Vasodilation and Sweating | 对高温的反应：血管舒张与出汗

When core temperature rises, the hypothalamus sends nerve impulses to the skin. Arterioles near the skin surface dilate, a response called vasodilation. More blood flows through the capillary networks close to the skin surface, so more heat is lost from the blood by radiation, conduction and convection.

当核心体温升高时，下丘脑向皮肤发送神经冲动。皮肤表面的小动脉扩张，这种反应称为血管舒张。更多血液流经靠近皮肤表面的毛细血管网，因此血液通过辐射、传导和对流散失更多热量。

Sweat glands also become active. Sweat is secreted onto the skin surface, and as it evaporates, it removes latent heat from the body. Evaporation is particularly effective in dry, breezy conditions, but less effective in humid conditions where the air is already saturated with water vapour.

汗腺也变得活跃。汗液分泌到皮肤表面，蒸发时带走体内的潜热。蒸发在干燥有风的环境中特别有效，但在空气已饱和水蒸气的潮湿环境中效果较差。

5. Responses to Cold: Vasoconstriction and Shivering | 对寒冷的反应：血管收缩与颤抖

When core temperature drops, arterioles in the skin constrict. This vasoconstriction reduces blood flow to the skin surface, so less heat is lost to the environment. Blood is diverted away from the skin and kept deeper inside the body, protecting the core organs.

当核心体温下降时，皮肤中的小动脉收缩。这种血管收缩减少了流向皮肤表面的血流量，因此向环境散失的热量减少。血液被转移到身体深处，保护核心器官。

Skeletal muscles may also undergo rapid, involuntary contractions called shivering. Shivering generates heat through increased respiration in muscle cells. In addition, erector muscles in the skin contract, causing hairs to stand on end. In furry mammals this traps an insulating layer of air, although the effect is very small in humans.

骨骼肌也可能进行快速、不自主的收缩，称为颤抖。颤抖通过增加肌肉细胞中的呼吸作用产生热量。此外，皮肤中的竖毛肌收缩，使毛发竖起。在有毛的哺乳动物中，这可以捕获一层隔热空气，但在人类中作用很小。

6. Role of Hair and Behavioural Responses | 毛发与行为反应的作用

In many mammals, the hair erector muscle response is important for insulation. Raising the hairs increases the thickness of the trapped air layer, reducing heat loss by convection and radiation. Humans have much less body hair, so piloerection produces only ‘goosebumps’ and provides little insulation.

在许多哺乳动物中，竖毛肌反应对隔热非常重要。毛发竖起会增加被捕获空气层的厚度，减少对流和辐射造成的热量散失。人类的体毛少得多，因此竖毛反应只会产生“鸡皮疙瘩”，几乎没有隔热作用。

Humans rely heavily on behavioural responses to control body temperature. Examples include moving into shade, removing extra clothing, curling up to reduce surface area, seeking shelter, putting on warm clothes, or drinking warm fluids. These behaviours are coordinated by the cerebral cortex rather than by the autonomic nervous system.

人类在很大程度上依靠行为反应来控制体温。例如移到阴凉处、脱去多余衣物、蜷缩身体以减少表面积、寻找庇护所、穿上保暖衣物或饮用温热液体。这些行为由大脑皮层协调，而不是由自主神经系统协调。

7. Hormonal Control of Body Temperature | 体温的激素调控

Hormones provide longer-term adjustments to body temperature. Thyroxine from the thyroid gland increases the basal metabolic rate, raising heat production throughout the body. It is released over hours and days, so its effect is slower than nervous responses.

激素对体温提供较长期的调节。来自甲状腺的甲状腺素提高基础代谢率，增加全身产热。它的释放需要数小时到数天，因此其作用比神经反应慢。

Adrenaline released from the adrenal medulla during cold stress also increases metabolic rate and promotes glycogen breakdown. In newborns and some hibernating mammals, brown adipose tissue carries out non-shivering thermogenesis. Brown fat mitochondria contain uncoupling proteins that allow respiration to produce heat instead of ATP.

冷应激时肾上腺髓质释放的肾上腺素也提高代谢率并促进糖原分解。在新生儿和某些冬眠哺乳动物中，棕色脂肪组织进行非颤抖性产热。棕色脂肪线粒体含有解偶联蛋白，使呼吸作用产生热量而不是 ATP。

8. Thermoregulation in Newborns and Ageing | 新生儿与衰老中的体温调节

Newborn babies have a high surface area to volume ratio, so they lose heat quickly to the surroundings. They cannot shiver effectively in the first weeks of life and rely heavily on brown fat for non-shivering thermogenesis. This is why keeping newborns warm is especially important.

新生儿的表面积与体积之比较大，因此向周围环境散热很快。他们在出生后最初几周无法有效颤抖，高度依赖棕色脂肪进行非颤抖性产热。因此给新生儿保暖尤为重要。

Elderly people may have a reduced ability to vasoconstrict and shiver, making them more vulnerable to hypothermia. Their temperature set point may also be slightly lower, and they may have a weaker febrile response. As a result, infections in older adults may not always present with a high fever.

老年人血管收缩和颤抖的能力可能下降，使它们更容易发生低体温。他们的体温设定点也可能略低，发热反应较弱。因此，老年人感染时并不总是出现高热。

9. Fever and the Set Point | 发热与体温设定点

Fever occurs when chemicals called pyrogens raise the hypothalamic set point. Pyrogens may come from pathogens, such as bacterial cell wall components, or from the body’s own immune cells. They often act by stimulating the production of prostaglandins in the hypothalamus.

当称为致热原的化学物质使下丘脑设定点升高时，就会发热。致热原可能来自病原体，如细菌细胞壁成分，也可能来自机体自身的免疫细胞。它们通常通过刺激下丘脑产生前列腺素而起作用。

The hypothalamus then treats normal body temperature as if it were too low. This triggers shivering and vasoconstriction, which is why a person feels cold and shivers during the onset of fever. When the set point returns to normal, vasodilation and sweating help cool the body.

下丘脑随后将正常体温视为过低。这会引发颤抖和血管收缩，因此人在发热初期会感到寒冷并颤抖。当设定点恢复正常时，血管舒张和出汗有助于身体降温。

10. Hypothermia and Hyperthermia | 低体温与高体温

Hypothermia occurs when core temperature falls below about 35 °C. As temperature drops, enzyme activity slows, nerve conduction becomes less efficient, and the person may become confused, drowsy or unconscious. Severe hypothermia can be fatal because the heart and respiratory centres stop working normally.

当核心体温降至约 35 °C 以下时，就会发生低体温。随着体温下降，酶活性减慢，神经传导效率降低，人可能出现意识模糊、嗜睡或昏迷。严重低体温可致命，因为心脏和呼吸中枢停止正常工作。

Hyperthermia occurs when core temperature rises above about 40 °C. Proteins and enzymes may denature, leading to heat stroke, which can damage the brain, heart and kidneys. Both hypothermia and hyperthermia exceed the normal corrective capacity of homeostasis and require medical intervention.

当核心体温升至约 40 °C 以上时，就会发生高体温。蛋白质和酶可能变性，导致热射病，这可能损害大脑、心脏和肾脏。低体温和高体温都超出了内稳态的正常纠正能力，需要医疗干预。

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The Control of Body Temperature | 体温的调控