Why do we sweat? - John Murnan

翻译人员: Lipeng Chen 校对人员: Vivian Hsia

The finish line's in sight and you put on an extra burst of speed.

终点线近在眼前了， 你开始加速。

As your legs pick up the pace, your breathing gets deeper,

你的腿逐渐变快， 呼吸也越来越深，

your heart pounds faster,

你的心脏跳动得更快，

and sweat pours over your skin.

你的汗如雨下。

How does this substance suddenly materialize

汗水是如何突然之间出现的？

and what exactly is its purpose?

它又有什么作用呢？

There are a number of scenarios that can make us sweat:

我们在很多情况下都会流汗：

eating spicy foods,

吃辣的东西，

nervousness,

紧张，

and when we're sick.

以及生病。

But exercise is probably the most familiar and common.

但是运动可能是 其中最寻常的一种情况。

In that case, sweating happens as a response to movement

在这种情况下，出汗是对于

triggered deep inside your cells.

体内细胞运动的一种反应。

As you increase your pace, your muscles work harder,

当你的速度加快， 你身上的肌肉更努力的工作，

increasing their demand for energy.

需要的能量也就越多。

A process called cellular respiration

一种名为细胞呼吸的过程

consumes glucose and oxygen to form ATP,

消耗葡萄糖和氧气来合成ATP，

the energy currency of the cell.

也就是细胞的“能量货币”。

Much of this process takes place in structures called mitochondria.

这一过程大部分发生在线粒体中。

The more you move,

你运动的越多，

the harder mitochondria work to supply your body with energy.

线粒体就越努力工作， 以支持你身体所需的能量。

All this work comes at a cost, though.

但是，这些工作都是有代价的。

As the cells break down the ATP, they release heat.

在细胞分解ATP时， 它们会同时散发热量。

The heat stimulates temperature sensors throughout your body.

这些热量刺激你体内的热量感应器。

Those receptors detect the excess heat being produced by your muscle cells

感应器接收了你 肌肉细胞所产生的多余热量，

and communicate that information to the hypothalamus,

并把这一信息传给

which regulates body temperature.

负责调控体温的下丘脑。

The hypothalamus responds

下丘脑对此作出反应，

by sending signals out through the sympathetic nervous system

通过遍布人体的交感神经系统，

to the sweat glands in your skin.

向皮肤中的汗腺发出信号。

These are distributed all over the body

这些汗腺遍布你的全身，

with especially high concentrations on the palms of your hands,

密集分布于手掌，

the soles of your feet,

脚掌，

and on your head.

和头部。

When a sweat gland first receives the signal,

当汗腺一开始接到信号时，

the fluid surrounding the cells in its coiled base

在汗腺底部细胞周围的液体中

contains high amounts of sodium and chloride.

含有大量的钠离子和氯离子。

The cells pump these ions into a hollow tube

这些细胞将这些离子打进一个

that runs through the sweat gland.

贯穿汗腺的小管。

Then, because it's saltier inside the tube than outside,

紧接着，由于管内比管外盐度更高，

water moves into the tube by osmosis.

渗透作用使水分进入管中。

As what's called the primary secretion builds up in the bottom of the tube,

随着这些主要分泌物 在小管的底部越积越多，

water pressure pushes it up into the long straight part of the duct.

压力使水上升到小管 长而直的部分中。

Before it seeps onto the skin,

在渗出皮肤之前，

cells lining the tube will reclaim as much salt as possible

小管周围的细胞 会尽可能多的吸收盐分

so the process can continue.

以确保这一过程继续进行。

The water in sweat absorbs your body's heat energy

汗液中的水分能吸收你身体的热量

and then evaporates off of you when it reaches the surface,

在到达肌肤表层时蒸发， 带走热量，

which in turn lowers your temperature.

以此来降低你的体温。

This process, known as evaporative cooling,

这一过程叫做蒸发冷却，

was an important adaptation for our ancestors.

是我们的祖先的 一种重要的适应性变化。

This cooling effect isn't only helpful during exercise.

这种冷却效应不光在运动中发挥作用。

We sweat in many other scenarios, too.

我们也在其他情况下出汗。

Eating particularly spicy food makes some people sweat profusely from their faces.

吃辣的东西会让 一些人脸部大量出汗。

That happens because spices trigger the same neural response in the brain

这是因为香辛料同样 会刺激大脑的一些神经反应，

that activates temperature receptors, which usually respond to increased heat.

这些反应会激活 感知热量增高的温度感应器。

Sweating is also part of the fight or flight response

出汗也是“战斗/逃跑反应”的一部分，

stimulated by stressful scenarios, like asking someone on a date

这种反应一般在焦虑的情况下会被激活， 例如邀请某人约会，

or interviewing for a job.

或是工作面试。

This happens because adrenaline stimulates muscle activity

这是因为肾上腺素刺激肌肉运动，

and causes blood vessels to widen,

使血管变宽，

two responses that increase heat and trigger the sweating response.

这两者都会增加热量， 从而触发流汗反应。

And sweating also occurs when we get sick.

我们在生病时也会出汗。

When we're feverish, we sweat because infections

当我们发烧时，我们会出汗是因为

stimulate the hypothalamus to increase muscle activity,

炎症使下丘脑增加肌肉运动，

which in turn releases more energy as heat.

并以散热的方式来释放热量。

That increases your overall temperature,

这会让你的体温整体上升，

a protective mechanism that makes your body less habitable for infectious agents.

这是一种保护机制， 使得传染源在你体内不易生存。

Like with running, sweating helps your body vent that heat.

就像跑步时一样， 流汗帮你带走热量。

When the fever's over or you've won your race,

当你退烧了或是赢了跑步比赛，

your temperature receptors sense the decrease in heat

热量感应器会感受到热量下降，

and the hypothalamus brings your sweating response to an end.

下丘脑也随之终止流汗反应。

In some cases, like after a run,

在一些情况下，例如跑完步后，

the hypothalamus also signals to your body

下丘脑也会向你的身体发送信号，

that you need to replenish the water that you've oozed out.

提醒你补充流失的水分。

So, when you're pushing yourself to reach that next goal,

所以，当你在尽力完成下一个目标时，

you can think of sweat as your body's very own calibrator,

你可以将汗水想成你身体的校准器，

enabling you to go that extra mile.

让你能够再多努力一点。