{"id":4862,"date":"2019-06-24T15:06:55","date_gmt":"2019-06-24T15:06:55","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/12-2-introduction-to-the-integumentary-system-3\/"},"modified":"2023-11-30T18:54:32","modified_gmt":"2023-11-30T18:54:32","slug":"12-2-introduction-to-the-integumentary-system-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/12-2-introduction-to-the-integumentary-system-3\/","title":{"raw":"10.2\u00a0Introduction to the Integumentary System","rendered":"10.2\u00a0Introduction to the Integumentary System"},"content":{"raw":" \r\n\r\n[caption id=\"attachment_3519\" align=\"aligncenter\" width=\"320\"]\"10.2.1\" Figure 10.2.1 The body as a canvas.<\/em>[\/caption]\r\n\r\n
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Art for All Eras<\/h1>\r\n<\/div>\r\nPictured in Figure 10.2.1, is Maud Stevens Wagner, a tattoo artist from 1907. Tattoos are not just a late 20th and early 21st century trend. They have been popular in many eras and cultures. Tattoos literally illustrate the biggest organ of the human body: the skin. The skin is very thin, but it covers a large area \u2014 about 2 m2<\/sup>\u00a0in adults. The skin is the major organ in the [pb_glossary id=\"2905\"]integumentary system[\/pb_glossary].\r\n
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What Is the Integumentary System?<\/h1>\r\n<\/div>\r\nIn addition to the skin, the\u00a0[pb_glossary id=\"2905\"]integumentary system[\/pb_glossary]<\/strong>\u00a0includes the\u00a0hair\u00a0and\u00a0nails, which are organs that grow out of the skin. Because the organs of the integumentary system are mostly external to the body, you may think of them as little more than accessories, like clothing or jewelry, but they serve vital physiological functions. They provide a protective covering for the body, sense\u00a0the environment, and help the body maintain\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary].\r\n
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The Skin<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"3521\"]skin[\/pb_glossary]<\/strong> is remarkable not only because it is the body\u2019s largest organ: the average square inch of skin has 20 blood vessels, 650 sweat glands, and more than 1,000 nerve endings. Incredibly, it also has 60,000 pigment-producing cells. All of these structures are packed into a stack of cells that is just 2 mm thick. Although the skin is thin, it consists of two distinct layers: the epidermis and dermis, as shown in the diagram (Figure 10.2.2).\r\n\r\n[caption id=\"attachment_3522\" align=\"alignnone\" width=\"587\"]\"Skin Figure 10.2.2 The epidermis is the thinner outer layer of skin, and the dermis is the thicker inner layer of skin. The latter contains structures such as blood vessels and sweat glands.<\/em>[\/caption]\r\n

Outer Layer of Skin<\/h2>\r\nThe outer layer of skin is the\u00a0[pb_glossary id=\"5991\"]epidermis[\/pb_glossary]<\/strong>. This layer is thinner than the inner layer (the dermis). The epidermis consists mainly of epithelial\u00a0cells, called\u00a0[pb_glossary id=\"3524\"]keratinocytes[\/pb_glossary],<\/strong>\u00a0which produce the tough, fibrous\u00a0protein\u00a0[pb_glossary id=\"3525\"]keratin[\/pb_glossary].<\/strong>\u00a0The innermost\u00a0cells\u00a0of the epidermis are [pb_glossary id=\"3163\"]stem cells[\/pb_glossary]\u00a0that divide continuously to form new cells. The newly formed cells move up through the epidermis toward the skin surface, while producing more and more keratin. The cells become filled with keratin and die by the time they reach the surface, where they form a protective, waterproof layer. As the dead cells are shed from the surface of the skin, they are replaced by other cells that move up from below. The epidermis also contains [pb_glossary id=\"3526\"]melanocytes<\/strong>[\/pb_glossary], the cells that produce the brown pigment melanin, which gives skin most of its colour. Although the epidermis contains some sensory receptor cells \u2014 called [pb_glossary id=\"3527\"]Merkel cells[\/pb_glossary] \u2014 it contains no nerves, blood vessels, or other structures.\r\n

Inner Layer of Skin<\/h2>\r\nThe\u00a0[pb_glossary id=\"5967\"]dermis[\/pb_glossary]<\/strong> is the inner, thicker layer of skin. It consists mainly of tough [pb_glossary id=\"2815\"]connective tissue[\/pb_glossary], and is attached to the epidermis by collagen fibres. The dermis contains many structures (as shown in Figure 10.2.2), including blood vessels, sweat glands, and hair follicles, which are structures where hairs originate. In addition, the dermis contains many sensory receptors, nerves, and oil glands.\r\n

Functions of the Skin<\/h2>\r\nThe skin has multiple roles in the body. Many of these roles are related to\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary]. The skin\u2019s main functions\u00a0are\u00a0preventing\u00a0water\u00a0loss from the body and serving as a barrier to the entry of microorganisms. Another function of the skin is synthesizing vitamin D, which occurs when the skin is exposed to ultraviolet (UV) light. Melanin in the epidermis blocks some of the UV light and protects the dermis from its damaging effects.\r\n\r\nAnother important function of the skin is helping to regulate body temperature. When the body is too warm, for example, the skin lowers body temperature by producing sweat, which cools the body when it evaporates. The skin also increases the amount of blood flowing near the body surface through vasodilation (widening of blood vessels), bringing heat from the body core to radiate out into the environment. The sweaty hair and flushed skin of the young man pictured in Figure 10.2.3 reflect these skin responses to overheating.\r\n\r\n[caption id=\"attachment_3529\" align=\"aligncenter\" width=\"400\"]\"Man Figure 10.2.3 Both sweating and flushing of the skin are signs that the skin is working to cool the body.<\/em>[\/caption]\r\n\r\n
\r\n\r\nHair<\/span>\r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_3532\" align=\"alignright\" width=\"200\"]\"Eyelashes\" Figure 10.2.4 Eyelashes protect the eyes.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"3531\"]Hair[\/pb_glossary]<\/strong> is a fibre found only in mammals. It consists mainly of keratin-producing [pb_glossary id=\"3524\"]keratinocytes[\/pb_glossary]. Each hair grows out of a [pb_glossary id=\"6015\"]follicle[\/pb_glossary] in the [pb_glossary id=\"5967\"]dermis[\/pb_glossary]. By the time the hair reaches the surface, it consists mainly of dead cells filled with [pb_glossary id=\"3525\"]keratin[\/pb_glossary]. Hair serves several homeostatic functions. Head hair is important in preventing heat loss from the head and protecting its skin from UV radiation. Hairs in the nose trap dust particles and microorganisms in the air, and prevent them from reaching the lungs. Hair all over the body provides sensory input when objects brush against it, or when it sways in moving air. Eyelashes and eyebrows (see Figure 10.2.4) protect the eyes from water, dirt, and other irritants.\r\n
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Nails<\/h1>\r\n<\/div>\r\nFingernails and toenails consist of dead [pb_glossary id=\"3524\"]keratinocytes[\/pb_glossary] filled with [pb_glossary id=\"3525\"]keratin[\/pb_glossary]. The keratin makes them hard but flexible, which is important for the functions they serve. [pb_glossary id=\"5495\"]Nails[\/pb_glossary]\u00a0prevent injury by forming protective plates over the ends of the fingers and toes. They also enhance sensation by acting as a counterforce to the sensitive fingertips when objects are handled. In addition, the fingernails can be used as tools.\r\n
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Interactions with Other Organ Systems<\/h1>\r\n<\/div>\r\nThe skin and other parts of the [pb_glossary id=\"2905\"]integumentary system[\/pb_glossary] work with other organ systems to maintain\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary].\r\n