Why do we sweat? - John Murnan

譯者: Helen Chang 審譯者: S Sung

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

終點線在望，你又加速了一陣

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

當你的雙腿加快步伐時 你的呼吸越來越深

your heart pounds faster,

你的心跳加快

and sweat pours over your skin.

汗水流淌在你的皮膚上

How does this substance suddenly materialize

為何突然滴下汗水？

and what exactly is its purpose?

流汗的目的究竟是什麼？

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

有很多場合會讓我們流汗：

eating spicy foods,

吃辛辣的食物

nervousness,

緊張

and when we're sick.

生病時

But exercise is probably the most familiar and common.

但運動可能最熟悉、最常見

In that case, sweating happens as a response to movement

在那種情況下 運動會觸發細胞的深處

triggered deep inside your cells.

而以出汗回應

As you increase your pace, your muscles work harder,

當你加快步伐時 你的肌肉會更努力工作

increasing their demand for energy.

增加對能源的需求

A process called cellular respiration

這是個細胞呼吸的過程

consumes glucose and oxygen to form ATP,

消耗葡萄糖和氧以形成 ATP （註：三磷酸腺苷）

the energy currency of the cell.

細胞的能量貨幣

Much of this process takes place in structures called mitochondria.

過程大部分發生在「粒線體」結構中

The more you move,

你動的越多

the harder mitochondria work to supply your body with energy.

粒線體就越賣力為你的身體提供能量

All this work comes at a cost, though.

儘管如此，這些全都要付出代價

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

熱量隨著細胞分解 ATP 而釋出

The heat stimulates temperature sensors throughout your body.

熱量刺激整個身體的溫度傳感器

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

這些受體檢測 肌肉細胞產生的多餘熱量

and communicate that information to the hypothalamus,

並將這些信息 傳給調節體溫的「下視丘」

which regulates body temperature.

來調節體溫

The hypothalamus responds

下視丘回應

by sending signals out through the sympathetic nervous system

將信號通過交感神經系統

to the sweat glands in your skin.

發送到到皮膚中的汗腺

These are distributed all over the body

汗腺遍佈全身

with especially high concentrations on the palms of your hands,

特別集中在手掌

the soles of your feet,

腳底

and on your head.

和頭部

When a sweat gland first receives the signal,

當汗腺首次接收到信號時

the fluid surrounding the cells in its coiled base

其捲曲基底細胞周圍的液體

contains high amounts of sodium and chloride.

含有大量的鈉和氯化物

The cells pump these ions into a hollow tube

細胞將這些離子

泵入穿過汗腺的中空管

that runs through the sweat gland.

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

由於管內的鹽分比管外更鹹

water moves into the tube by osmosis.

水「滲透」入管內

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

隨著「主要分泌物」在管底部積聚

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

水壓將其推上長長直直的管道

Before it seeps onto the skin,

在滲透到皮膚表面以前

cells lining the tube will reclaim as much salt as possible

襯管內的細胞盡可能地回收鹽分

so the process can continue.

讓這過程得以繼續

The water in sweat absorbs your body's heat energy

汗水中的水分吸收人體熱能

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

當它到達表面時會蒸發掉

which in turn lowers your temperature.

從而降低體溫

This process, known as evaporative cooling,

這個過程稱為「蒸發冷卻」

was an important adaptation for our ancestors.

是我們祖先的重要的進化

This cooling effect isn't only helpful during exercise.

冷卻效應不僅作用在運動過程中

We sweat in many other scenarios, too.

我們還在其他許多場合出汗

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

吃特別辛辣的食物 會讓一些人的臉部大量流汗

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

這是因為香料在大腦中 引發相同的神經反應

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

激發體溫感受器 通常會增加熱量的產出

Sweating is also part of the fight or flight response

出汗也是「戰鬥或逃跑」反應的一部分

stimulated by stressful scenarios, like asking someone on a date

來自壓力情境的刺激

像是邀請某人約會或面試工作

or interviewing for a job.

This happens because adrenaline stimulates muscle activity

這是因為腎上腺素刺激肌肉活動

and causes blood vessels to widen,

導致血管擴張

two responses that increase heat and trigger the sweating response.

兩種反應增加熱量並引發出汗反應

And sweating also occurs when we get sick.

我們生病時也會出汗

When we're feverish, we sweat because infections

我們發燒時會出汗

因為感染會刺激下視丘增加肌肉活動

stimulate the hypothalamus to increase muscle activity,

which in turn releases more energy as heat.

從而釋放出更多的熱量

That increases your overall temperature,

這會增加你的整體溫度

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

是一種保護機制 使你的身體不適合傳染源生存

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

就像跑步一樣 出汗有助於身體排出熱量

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

退燒後，或你贏了比賽後

your temperature receptors sense the decrease in heat

你的體溫感受器會感受到熱量的減少

and the hypothalamus brings your sweating response to an end.

下視丘會結束你的出汗反應

In some cases, like after a run,

在某些情況下，如跑步後

the hypothalamus also signals to your body

下視丘也會向你的身體發出信號

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

提醒你需要補充流失的水分

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

所以當你盡力達到下一個目標時

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

你可以將汗水看成是自己的校準器

enabling you to go that extra mile.

使你能夠更努力一些