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人类的皮肤

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Body organs aren't all internal like the brain or the heart. There's one we wear on the outside. Skin is our largest organ—adults carry some 8 pounds (3.6 kilograms) and 22 square feet (2 square meters) of it. This fleshy covering does a lot more than make us look presentable. In fact, without it, we'd literally evaporate.
皮肤不像大脑和心脏一样全是内部器官。有一部分我们是“穿”在外面的。皮肤是我们最大的器官——一个成人的皮肤约有8磅重(约3.6千克)22平方英尺(约2平米)。这种肉质的表面可绝不仅是让我们看起来体面。事实上,没有它的话我们肯定会死掉。

Skin acts as a waterproof, insulating shield, guarding the body against extremes of temperature, damaging sunlight, and harmful chemicals. It also exudes antibacterial substances that prevent infection and manufactures vitamin D for converting calcium into healthy bones. Skin additionally is a huge sensor packed with nerves for keeping the brain in touch with the outside world. At the same time, skin allows us free movement, proving itself an amazingly versatile organ.
皮肤扮演着防水层,隔离盾的角色,保护我们的身体免受极限温度,破坏性的阳光和有害化学物质的侵害。它还会分泌抗菌物质来预防感染并且产生维他命D将钙质转化成健康的骨骼。除此之外皮肤还是汇集了众多神经元的感觉器官,能够让大脑感受到外面世界。与此同时,皮肤能让我们自由运动,这体现了皮肤是如此神奇的多功能器官。

 

 

Skin is made up of three layers. The outermost is the epidermis. This consists mainly of cells called keratinocytes, made from the tough protein keratin (also the material in hair and nails). Keratinocytes form several layers that constantly grow outwards as the exterior cells die and flake off. It takes roughly five weeks for newly created cells to work their way to the surface. This covering of dead skin is known as the stratum corneum, or horny layer, and its thickness varies considerably, being more than ten times thicker on the soles of the feet than around the eyes. The epidermis harbors defensive Langerhans cells, which alert the body's immune system to viruses and other infectious agents.
皮肤分为三层。最外面的一层叫表皮。这一层主要由粗质角蛋白(也是头发的主要成分)构成的角化细胞组成。角化细胞形成多层细胞层随着最外层的细胞死亡消失不断往外生长。新生的细胞只要用5周的时间就可以成为最外层。这层死亡的覆盖层称之为组织层或者叫做角质层,其厚度跨度很大,脚后跟的上角质层的厚度是眼部的10倍。表皮包含保护性的朗格罕氏细胞,能够向身体的免疫系统预警病毒和其他形式感染的入侵。

The epidermis is bonded to a deeper skin layer below known as the dermis, which gives the organ its strength and elasticity thanks to fibers of collagen and elastin. Blood vessels here help regulate body temperature by increasing blood flow to the skin to allow heat to escape, or by restricting the flow when it's cold. A network of nerve fibers and receptors pick up feelings such as touch, temperature, and pain, relaying them to the brain.
跟表皮连接的深层皮肤叫真皮,由含有胶原蛋白和弹性蛋白构成的纤维能够提供细胞活力和延展性。此处的血管通过加速血液流动带走多余的热量及当温度寒冷时限制血液流动等方式调节体温。神经纤维和接收器形成的网络系统接收诸如触摸、温度、疼痛这样的感觉,传递给大脑。

The dermis houses hair follicles and glands with ducts that pass up through the skin. Sweat glands bring down internal temperature through perspiration while ridding the body of the waste fluids urea and lactate. Apocrine glands, which develop during puberty, produce a scented sweat linked to sexual attraction that can also cause body odor, especially around the armpits. Sebaceous glands secrete oil-like sebum for lubricating the hair and skin.
真皮包含了毛囊和纵贯皮肤的带导管的腺体。汗腺通过出汗降低体内温度同时去除体内废弃的尿素和乳酸盐。青春期生长的泌离腺产生带有可以吸引异性的特殊气味的汗液,也可以导致腋臭尤其是在腋窝附近。皮脂腺分泌油状皮脂润滑毛发和皮肤。

The skin's base layer is the subcutis, which includes a seam of fat laid down as a fuel reserve in case of food shortage. It also works as insulation and cushions us from knocks and falls.
皮肤最里层的部分叫皮下组织,包含狭长的脂肪层——作为缺血时的储备。这一层也可以作为我们摔打时的隔离层或缓冲垫。

Skin Color
肤色

 


Skin color is due to melanin, a pigment produced in the epidermis to protect us from the sun's potentially cancer-causing ultraviolet (UV) rays. Dark-skinned people produce more numerous and deeper-colored melanin particles. People with the darkest complexions are native to tropical regions, particularly those with few densely forested areas.
皮肤的颜色取决于黑色素。这是一种产生于表皮的色素,能够保护我们免受来自紫外线的侵袭。紫外线正是来自太阳的潜在致癌物。深色皮肤的人产生更多深色的黑色素。肤色最深的人是生长于森林覆盖最低的赤道地区。

Fair skin is an adaptation found in people from northern latitudes where solar rays are relatively weak. Here the benefits of dark skin are outweighed by the need for bone-strengthening vitamin D, produced through exposure to UV rays. But hotter, sunnier environments bring the risk of serious skin damage. Australia, where the majority of the population is of northern European descent, has the world's highest rates of skin cancer, accounting for more than 80 percent of all cancers diagnosed there each year.
白皙皮肤的人种来自太阳光相对弱的北纬地区。这个地区人们通过照射紫外线来获取骨骼生长所需要的维他命D,所以深肤色的优势已凸显不出。然而更热阳光更充足的地区也具有伤害皮肤的危险。澳大利亚这个大部分人口都是北欧后裔的国家拥有世界最高的皮肤癌发病率,当地的皮肤癌患者约占到所有癌症患者的80%。

标签:皮肤 人类
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2010-06-24 23:03 编辑:kuaileyingyu
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