章节大纲

  • lesson content

    What is waterproof and the body's largest organ ?
    ::什么是防水的 身体最大的器官?

    Your skin. The skin is a living (though the outermost layer is made of dead cells), constantly regenerating organ that has numerous functions.
    ::你的皮肤。皮肤是活的(虽然最外层是死细胞组成的), 不断的再生器官, 有多种功能。

    Skin
    ::皮肤

    The skin is a vital organ that covers the entire outside of the body, forming a protective barrier against and injuries from the environment. The skin is the body's largest organ, and it is only about 2 mm thick. It shields the body against heat, light, injury, and infection. The skin also helps regulate body temperature, gathers sensory information from the environment, stores , fat, and vitamin D , and acts as a physical barrier in protecting us from diseases.
    ::皮肤是覆盖整个身体外部的重要器官,形成一种抵御和伤害环境的防护屏障。皮肤是身体最大的器官,只有2毫米厚。它保护身体免受热、光、伤害和感染。皮肤也有助于调节身体温度,收集来自环境、储存、脂肪和维生素D的感官信息,并成为保护我们免受疾病的物理屏障。

    Your skin is constantly in contact with your external environment, so it gets cut, scratched, and exposed to radiation such as ultraviolet (UV) light. You also naturally shed many skin every day. Your body replaces damaged or missing skin cells by growing more of them through the process of . Two distinct layers make up the skin: the epidermis and the dermis . A fatty layer, called subcutaneous tissue or hypodermis (below skin), lies under the dermis, but it is not considered to be part of your skin. The layers that make up your skin are shown in the Figure .
    ::您的皮肤经常与外部环境接触, 因此它会切开, 划伤, 并暴露于辐射之下, 比如紫外线( UV) 光线( 紫外线) 。 您还自然地每天剥下许多皮肤。 您的身体会通过通过过程的生长来替换受损或缺失的皮肤细胞。 皮肤上有两个不同的层: 皮层和皮层。 一个脂肪层, 叫做皮下组织或皮下组织( 皮肤下) , 位于皮肤下, 但不被认为是皮肤的一部分 。 您皮肤上的层在图中显示 。

    lesson content

    The structure of the skin. The structures of the epidermis, dermis, and the subcutaneous tissue. Note how there are no blood vessels in the epidermis.
    ::皮肤结构, 皮皮、 皮肤和皮下组织的结构。 注意皮下没有血管。

    The color, thickness, and texture of skin vary over the body. There are two general types of skin: thin and hairy, which is the most common type on the body, and thick and hairless, which is found on parts of the body that are used heavily and experience a lot of friction such as the palms of the hands or the soles of the feet.
    ::皮肤的颜色、厚度和纹理在身体上各有不同。 皮肤有两种一般的皮肤类型:薄和毛,这是身体上最常见的类型;厚和毛,在大量使用身体的部位上发现,并且经历了许多摩擦,例如手掌或脚底的摩擦。

    Epidermis
    ::流行病

    Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of many layers of epithelial cells, as shown in the Figure .
    ::Epidermis是皮肤最外层的一层,它构成防水、身体表面的保护性包装,由许多层的上皮细胞组成,如图所示。

    lesson content

    The epidermis is made up of many layers of epithelial cells. The uppermost layer is made up of many flat, dead, keratin-filled cells called keratinocytes. Every day, thousands of keratinocytes get scraped off the surface of your skin and are replaced by cells that move up from lower layers.
    ::后皮细胞由许多层的上皮细胞组成。 上皮细胞由许多平坦的、死灰的、填满氯酸盐的细胞组成,称为乳腺细胞。 每天,成千上万的乳腺细胞从皮肤表面被刮掉,取而代之的是从下皮细胞向上移动的细胞。

    The epidermis is divided into several layers, and epithelial cells are formed through mitosis in the lowest layer. The epithelial cells move up through the layers of the epidermis, changing shape and composition as they differentiate and become filled with a tough, fibrous called keratin . At this point, the cells are called keratinocytes. Keratinocytes at the surface of the epidermis form a thin layer of flattened, dead cells (the stratum corneum in the Figure ). Although the top layer of epidermis is only about as thick as a sheet of paper, it is made up of 25 to 30 layers of keratinocytes. Keratinocytes get scraped off through everyday activities and are usually shed about a month after they reach the surface of the epidermis.
    ::上皮细胞分为几层, 上皮细胞通过最小层的松化形成。 上皮细胞通过上皮细胞的层向上移动, 形状和构成随着它们的不同而变化, 并被一个硬的、 纤维化的、 叫做Keratin 的细胞填满。 此时, 这些细胞被称作乳腺细胞。 在上皮细胞表面的Keratino细胞形成一层薄薄的扁状死细胞( 图中的直角角角角)。 虽然上皮细胞的厚度只有一张纸厚, 由25至30层的红皮细胞组成。 皮肤细胞通过日常活动被刮掉, 通常在到达上皮细胞表面后一个月左右被剥出。

    The epidermis also contains cells called melanocytes that produce the pigment melanin . Melanin is the brownish pigment that gives skin and hair their color. Melanocytes are located in the bottom layer of the epidermis: the stratum basale, shown in the Figure . The difference in skin color between light-skinned people and dark-skinned people is not due to the number of melanocytes in their skin, but to the melanocytes' level of activity. The amount of melanin produced in a person’s skin is dependent on his or her genetics and the amount of ultraviolet (UV) light exposure. Melanin absorbs UV rays from the sun or other sources of UV light such as a tanning bed. When UV light penetrates the skin and damages , the damaged DNA triggers the synthesis of more melanin. The skin also makes vitamin D by absorbing energy from UV light. Melanin acts like a UV filter, so the more melanin there is in a person’s skin, the more time the person has to spend in sunlight to produce the same amount of vitamin D as a person with less melanin in their skin.
    ::上皮层也包含产色色色色色的细胞。 美兰素是褐色色色素, 使皮肤和毛发染色。 美兰素位于皮层底层: 图中显示的是底色; 浅皮人和深皮人之间的肤色差异不是由于皮肤上的青皮动物数量,而是由于青皮动物的活动水平。 一个人皮肤上生产的美兰素数量取决于他或她的基因和紫外线照射量。 梅兰宁吸收了太阳或其他紫外线光源的紫外线光线,如晒黑床。 当紫外线穿透皮肤和损伤时, 受损害的DNA触发了更多黑皮的合成。 皮肤也通过吸收紫色光的能量而使维他维他命D成为维他命。 Melanin的行为像紫外线过滤器一样, 因此, 在一个人的皮肤中, 较薄的薄线素在一个人的皮肤上消耗量越少, 其光线在他身上消耗的光度就越少。

    The epidermis also contains cells that take up and process certain marker proteins (called antigens) from microbes that enter through the skin. This helps the immune system recognize the microbe as an intruder and mount an attack on it. The epidermis contains no , so the lower portion of the epidermis is nourished by from the blood vessels of the dermis.
    ::皮层外皮还包含细胞,细胞接收和处理通过皮肤进入皮肤的微生物的某些标记蛋白(称为抗原),这有助于免疫系统承认微生物是入侵者,并对它发动攻击。皮层内没有,因此皮层下部由皮肤血管养成。

    Structure and Function of Dermis
    ::衍生物的结构和功能

    The dermis is the layer of skin directly under the epidermis that is made of tough, elastic connective tissue . The dermis is tightly connected to the epidermis by a membrane made of collagen fibers. The dermis contains the hair follicles , sweat glands , sebaceous glands , and blood vessels. It also holds many nerve endings that provide the sense of touch, pressure, heat, and pain. Tiny , called arrector pili, contract and pull on hair follicles, which cause hair to stand up. This can happen when you are cold or afraid, and the resulting little “bumps” in the skin are commonly called goose bumps.
    ::皮肤是由坚硬的弹性连接组织制成的皮层。 皮层与皮层紧密相连。 皮层由用碳基纤维制成的膜与皮层紧密相连。 皮层包含毛发泡、 汗毛腺、 羊皮和血管。 皮层还包含许多神经端, 提供触摸、 压力、 热和疼痛感。 细微的, 叫做羊皮, 合同和拉扯毛发, 导致毛发站起来。 这可能发生在你寒冷或害怕时, 导致皮肤上的小“ 肿块” 通常被称为鹅斑。

    The dermis has two layers, each of which contains different structures:
    ::皮肤分为两层,每层结构不同:

    The papillary region (upper layer) is made up of loose connective tissue and contains touch receptors, which communicate with the . It is named for its finger-like projections called papillae, which extend toward the epidermis and help secure the dermis to the epidermis. The papillae can be seen in the Figure . The papillae provide the dermis with a "bumpy" surface that causes distinctive friction ridges. They are called friction ridges because they help the hand or foot to grasp things by increasing friction. Friction ridges, as shown in the Figure , occur in patterns that are unique to the individual, making it possible to use fingerprints or footprints as a means of identification.
    ::毛虫区域( 上层) 由松散的连接组织组成, 含有触摸感应器, 这些感应器与它交流。 它的名字来自它的指形投影, 叫做papillae, 指向粘膜, 帮助保护皮质。 papillae 可以在图中看到。 papillae 向皮肤提供一种“ bumpy” 表面, 造成独特的摩擦脊。 它们被称为摩擦脊, 因为它们通过增加摩擦帮助手或脚抓住东西。 图中显示, 摩擦脊以个人独特的模式出现, 从而有可能使用指纹或脚印作为识别手段。

    lesson content

    A close-up image of a fingerprint. The friction ridges that originate in the dermis and make up the whorls and lines of finger and toe prints are clearly visible. Both fingers and toes have these distinctive ridges.
    ::指纹的近距离图像。摩擦脊源自于皮肤,构成指尖和脚趾指纹的胡作非为和线条的摩擦脊明显可见。手指和脚趾都有这些独特的脊。

    The reticular region (lower layer) is made of dense, elastic fibers (collagen), which contain the hair follicles and , nerves, and glands. It gets its name from the dense concentration of protein fibers that weave throughout it. These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Heat, cold, and pressure receptors , nails, and blood vessels are also located in this region. Tattoo ink is injected into the dermis. Stretch marks are also located in the dermis.
    ::视网膜区域(低层)由稠密、弹性纤维(collagen)组成,其中含有毛发泡、神经和腺,其名称来自其整个编织的蛋白纤维密度的浓度,这些蛋白纤维赋予其强度、可伸缩性和弹性的皮质特性。热、冷和压力受体、指甲和血管也位于该地区。纹身墨被注入皮肤。伸缩标记也位于皮肤中。

    Glands and Follicles
    ::地表和冰块

    Glands and follicles open out into the epidermis, but they originate within the dermis. A sebaceous gland, also known as an oil gland, secretes an oily substance, called sebum , into the hair follicle. Sebum is made of and the debris of dead lipid-producing cells. The word sebum comes from the Latin word for fat, or tallow. It “waterproofs” hair and the skin surface to prevent them from drying out. It can also inhibit the growth of microorganisms on the skin. Sebum is the cause of the oily appearance of skin and hair. It is odorless, but the breakdown of sebum by can cause odors. A sebaceous gland is shown in the Figure . If a sebaceous gland becomes plugged and infected, it develops into a pimple (also called acne).
    ::地壳和鹅卵石向后皮裂开,但是它们来自皮肤。一个叫做油腺的沙斑腺,将一种油质物质,即叫塞布姆(sebum),隐藏在毛发柱中。塞布姆是用死脂肪产细胞制造的,碎片来自死脂肪产细胞。塞布姆的字词来自拉丁语中的脂肪或高地。“防水”毛发和皮肤表面,以防止它们干涸。它也可以抑制皮肤微生物的生长。塞布姆是皮肤和毛发油状出现的原因。它是无味的,但塞布姆的分解可以引起臭味。图中显示的是塞巴塞格兰。如果塞巴切的腺被塞住和感染,它会发展成一个小便道(也称为“acne ”) 。

    lesson content

    A sebaceous gland and its associated hair follicle. Sebum acts to protect and waterproof hair and skin and keep them from becoming dry, brittle, and cracked.
    ::腐烂的甘蓝及其相关的毛发泡,塞邦采取行动保护、防水的毛发和皮肤,防止它们干燥、易碎和裂开。

    Sweat glands open to the epidermal surface through the skin pores. They occur all over the body and are controlled by the sympathetic . Evaporation of sweat from the skin surface helps lower the skin temperature, which in turn helps to control body temperature. The skin also functions as an excretory organ because it releases excess water, salts, and other wastes in sweat. A sweat gland is shown in the Figure . There are two types of sweat glands: eccrine glands and apocrine glands. Eccrine glands are the “regular” sweat glands that release sweat to cool the body. Apocrine glands are larger than eccrine glands and are located in the armpits and groin areas. They effectively act as scent glands because they produce a solution that bacteria break down to produce "body odor."
    ::皮肤表面的汗水蒸发有助于降低皮肤温度,这反过来又有助于控制体温。皮肤的皮肤还起到排泄器官的作用,因为它释放出过多的水、盐类和其他在汗中的废物。图中显示了一种汗水腺。有两种类型的汗水腺:乳液腺和甲状腺。羊腺是释放出汗液的“普通”汗腺,以冷却身体。水浆腺的干燥面积大于乳液腺,位于腹部和腹部区域。它们实际上起到嗅觉作用,因为它们产生一种溶液,细菌破裂以产生“体臭”。

    Mammary glands are the organs that, in female mammals , produce milk to feed their young. Mammary glands are enlarged and modified sweat glands and are a major characteristic of mammals.
    ::在雌性哺乳动物中,哺乳腺是生产牛奶喂养其幼年的器官,哺乳腺扩大并改变出汗腺,是哺乳动物的主要特征。

    lesson content

    The location of sweat glands in the dermis. Note that the sweat glands are called sudoriferous glands in this image.
    ::注意,在这种图象中,汗腺被称为水底腺。

    Subcutaneous Tissue
    ::密质组织

    The subcutaneous tissue (also called the hypodermis) lies below the dermis and contains fat and loose connective tissue that holds larger blood vessels and nerves. Its purpose is to attach the skin to underlying and muscle as well as to supply the skin with blood vessels and nerves. This layer is important to the regulation of body temperature. It is mostly made up of adipose tissue (which is made up of fat cells or adipocytes); the subcutaneous tissue contains about 50 percent of the body’s fat. The functions of subcutaneous tissue include insulation and the storage of nutrients . The size of this layer varies throughout the body and from person to person.
    ::皮下组织(也称为皮下组织)位于皮肤下方,内含脂肪和松散的连接组织,内含较大的血管和神经。其宗旨是将皮肤与底部和肌肉绑在一起,并为皮肤提供血管和神经。这一层对于调节身体温度十分重要。它主要由脂肪组织(由脂肪细胞或二细胞组成)组成;皮下组织包含大约50%的身体脂肪。皮下组织的作用包括绝缘和营养素储存。这一层的大小在身体和人之间各不相同。

    Skin and Homeostasis
    ::皮肤和软骨

    The skin has multiple roles in including protection, control of body temperature, sensory reception, water balance , synthesis of vitamins and , and absorption of materials. The skin's main functions are to serve as a barrier to the entry of microbes and and to prevent water and extracellular fluid loss. Acidic secretions from skin glands also stop the growth of on the skin. Melanocytes form a second barrier: protection from the damaging effects of UV radiation . When a microbe gets into the skin (or when the skin is cut) an immune system reaction occurs.
    ::皮肤在保护、控制身体温度、感官接收、水平衡、维他命和维他命合成以及材料吸收等方面有多重作用,皮肤的主要功能是作为进入微生物的障碍,防止水和细胞外液体流失,皮肤腺酸性分泌还阻止皮肤的生长。梅拉诺细胞形成第二个屏障:防止紫外线辐射的有害影响。当微生物进入皮肤(或皮肤切除时)时,会发生免疫系统反应。

    Heat and cold receptors are located in the skin. When the body temperature rises, the hypothalamus sends a nerve signal to the sweat-producing skin glands, causing them to release sweat onto the skin surface. The evaporation of sweat helps reduce the temperature of the skin surface, which cools the body. The hypothalamus also causes dilation of the blood vessels of the skin, allowing more to flow into those areas, causing heat to be released from the skin surface. When body temperature falls, the sweat glands constrict, and sweat production decreases. If the body temperature continues to fall, the body will start to generate heat by raising the body's metabolic rate and by causing the muscles to shiver.
    ::皮肤是热感和冷感应器。当身体温度上升时,下脑膜会向出汗的皮肤腺发出神经信号,导致它们向皮肤表面释放出汗。汗的蒸发有助于降低皮肤表面的温度,使身体冷却。下脑膜还导致皮肤血管膨胀,允许更多的血流进入这些区域,导致皮肤表面释放热量。当体温下降时,汗腺收缩,汗液产量下降。如果身体温度继续下降,身体将开始通过提高身体代谢率和造成肌肉颤抖来产生热量。

    The homeostatic functions of the skin include the following:
    ::皮肤的恒定功能包括:

    • Protection of the body’s internal tissues and organs.
      ::保护身体的内部组织和器官。
    • Protection against invasion by infectious organisms .
      ::防止感染性生物侵入。
    • Protection of the body from dehydration.
      ::保护身体不脱水。
    • Protection of the body against large changes in temperature.
      ::保护身体免受温度大幅变化的影响。
    • Excretion of wastes through sweat.
      ::通过汗水排出废物。
    • Acts as a receptor for the of touch, pressure, pain, heat, and cold.
      ::作为触摸、压力、疼痛、热和寒冷的受体
    • Makes vitamin D through exposure to UV radiation.
      ::通过接触紫外线辐射使维生素D成为维生素D。
    • Stores water, fat, and vitamin D.
      ::储水、脂肪和维生素D

      

     

    Summary
    ::摘要

    • The epidermis provides an outer layer of protection and also contains melanocytes, which protect the body against UV rays.
      ::上皮动物提供外层保护,并含有甲状腺素,保护身体免受紫外线的侵袭。
    • The dermis contains hair follicles, sweat glands, sebaceous glands, and blood vessels.
      ::皮肤中含有毛发泡、汗腺、精细腺和血管。
    • The hypodermis is not considered part of your skin, but its main purpose is to attach the skin to underlying bone and muscle as well as to supply the skin with blood vessels and nerves.
      ::皮下皮不被视为皮肤的一部分,但其主要目的是将皮肤附在骨骼和肌肉上,并为皮肤提供血管和神经。

    Review
    ::回顾

    1. How do epithelial cells change as they move up through the epidermis?
      ::肾上腺细胞在通过皮皮层移动时 是如何变化的?
    2. What are the two types of sweat glands?
      ::这两类汗腺是什么?
    3. What kind of glands are mammary glands?
      ::哺乳腺是什么样的腺?
    4. Why are there differences in skin color between humans?
      ::为什么人类的肤色有差异?
    5. How does the epidermis aid the immune system?
      ::突袭如何帮助免疫系统?