The science of skin - Emma Bryce

翻译人员: David Zhang 校对人员: Cissy Yun

“最精致的衣服是人的皮肤， 当然，社会不仅仅要求你穿着这件衣服一马克·吐温”

Between you and the rest of the world lies an interface

我们的身体和自然界之间 有一层分界线，

that makes up 16% of your physical weight.

占体重的16%，

This is your skin, the largest organ in your body:

它就是我们身上面积最大的器官： 皮肤。

laid out flat, it would cover close to 1.7 square meters of ground.

摊开铺平，能覆盖约1.7平方米。

Its purpose may seem obvious— to keep our insides in.

皮肤的作用显而易见—— 使我们的身体保持一个整体,

But a look beyond the surface

但更深入看,

reveals that it plays a surprising number of roles in our lives.

会发现皮肤在我们的生命中 起到令人震惊的作用。

First, the basics.

首先最基本的是

Skin is the foundation of the integumentary system,

皮肤是表皮系统基本组成部分，

which also incorporates your hair, nails, and specialized glands and nerves.

同时还包括还包括头发、指甲、 特定的腺体和神经。

Made up of three layers,

皮肤分为3层：

the epidermis,

表皮层

dermis,

真皮层

and hypodermis,

和皮下组织。

skin’s thickness varies from 0.5 millimeters at its thinnest

皮肤最薄处为0.5mm，

and up to four millimeters at its thickest.

最厚处为4mm。

It also carries out three key functions:

皮肤还具有3个关键作用：

protecting,

保护作用

regulating,

调节作用

and sensing the world beyond its limits.

以及对外部环境的感知作用。

On a daily basis, its huge surface processes hundreds, if not thousands,

每天，我们的身体会处理

成百上千次的体表感知，

of physical sensations,

relying mostly on large, pressure-sensitive skin components

主要由较大的对压力敏感的组织完成

called Merkel cells.

叫做梅克尔细胞。

In your fingertips alone,

在我们的指尖上，

there are 750 Merkel cells per each square-centimeter of skin,

每1cm²有750个梅克尔细胞

coupled with over 2,500 receptors that give you your sense of touch.

以及构成触感的2500多个受体。

This surface is also the body’s first major line of defense.

皮肤也是身体的第一道防线，

Without it, you’d be a soggy mass of tissue and fluids,

没有皮肤， 我们就是一滩组织和体液，

fatally exposed to the elements.

致命的暴露于各种环境下。

Skin effectively seals off your insides

皮肤有效的将你的身体组织 保持在内部，

and also absorbs pressure and shock

还能够承受外界的压力和冲击。

with flexible collagen that makes up most of its dermal layer.

这得益于真皮层的主要组成： 具有高柔韧性的胶原蛋白

The epidermis is made up mainly of skin cells called keratinocytes

表皮主要由角质细胞构成，

that are completely replaced every four weeks.

每4星期完全更新一次。

As new cells form at the base of the epidermis, older ones are pushed up.

随着新细胞在底部形成， 旧细胞会被推出。

When these cells move upwards,

细胞在向上移动过程中，

they’re filled with a hardened protein called keratin.

会被填充一种硬化的蛋白质， 叫做角蛋白。

Once they reach the surface,

一旦到达表面，

they form a tightly-overlapping, waterproof layer

它们会形成一层紧密重叠的防水层，

that’s difficult for invading microbes to breach.

使得微生物难以进入。

Any harmful microbes that make it into the epidermis

若有害微生物得以侵入,

will encounter Langerhans cells.

就会遇到郎格汉斯细胞。

This group of protective skin cells detects invaders

这种保护性细胞会侦测入侵者，

and communicates their presence to resident immune system T-cells,

并且将其报告给免疫 T 細胞

which react by launching an immune response.

启动免疫反应。

A crucial feature of this immune defense

这个免疫防卫机制的最关键一点是，

is the several thousand species of microorganisms

有数千种存在于

that inhabit the planes,

皮肤表面，

folds,

褶皱

and crevices of your skin.

和皮肤小裂缝的微生物。

These microbes, which include bacteria and fungi,

包括细菌和真菌的这些微生物

thrive in the sebum,

在皮脂内十分活跃，

an oily substance that’s secreted onto the skin’s surface

由紧贴在真皮内的皮脂腺分泌到

by sebaceous glands nestled inside the dermis.

皮肤表面的油性物质。

These skin microbes keep the immune system in a state of constant surveillance,

这些皮肤微生物使得 免疫系统一直处于活跃状态，

ensuring that it’s ready to react if the body really is at risk.

确保在身体处于危险的情况下 能够及时响应。

Beyond this protective role,

除了充当保护的角色，

your skin is also a sensory organ that helps regulate your body’s temperature,

你的皮肤也是帮助调节你体温的感官，

two roles that are closely interlinked.

两种功能紧密相连。

Nerves detect whether your skin is warm or cold

神经会检测你的皮肤是冷还是暖，

and communicate that information to your brain.

并且将感知信息传达给大脑，

In return, the brain instructs localized blood vessels

大脑则进行回应调节局部血管：

to either expand if the body is too warm,

如果身体热时扩张血管

releasing heat from the blood through the skin,

则通过皮肤从血液释放热量，

or to constrict if the body is cold, which retains heat.

如果身体冷时则收缩血管 以保留热量。

At any given time, up to 25% of the body's blood is circulating through the dermis,

在任何时间， 超过25%的身体血液通过真皮循环

making this process extremely efficient.

这使得调节体温这个过程非常有效。

Under warm conditions,

感到热时，

the skin’s sweat glands will secrete sweat via ducts onto the surface,

皮肤的汗腺分泌的汗液 将经由腺体的管道到达表面，

transferring heat out of the body.

将热量带出体外。

Hair can also be stimulated to conserve or release body warmth.

毛发也可以受刺激， 保留或者释放身体的热量。

The average human has 5 million hair follicles

平均每个人有5百万毛囊，

embedded everywhere on the body

除了你的手掌和脚掌

except the palms of your hands and soles of your feet.

身体的每一个地方都有。

Ninety to 150,000 of those are on your scalp,

在你的头皮上有9万~15万个毛囊

where they help shield the large surface area of your head

头皮会保护很大面积的头部远离

from physical damage and sunburn.

物理伤害和晒伤。

When you're cold, tiny muscles called arrector pilli

当你冷时叫做立毛肌的小型肌肉

cause hair to stand upright across the body.

会使你身体的毛发竖起来。

That’s the phenomenon known as goosebumps and it traps body heat close to your skin.

这种现象叫起鸡皮疙瘩， 这可以吸收身体附近的热量。

Skin’s vast surface isn’t just a shield;

皮肤的巨大的表面 不仅仅是一个防护盾，

it also enables us to interact and connect with the world.

它还使我们与这个世界互连，

Its multifunctional layer cools us down and keeps us warm.

其多个功能层可以降温和保持体温。

The integumentary system may be many things,

表皮系统有很多功能，

but it’s certainly more than skin deep.

它对我们身体的帮助， 绝对比表皮更深。