{"id":4270,"date":"2017-03-28T18:57:59","date_gmt":"2017-03-28T18:57:59","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&p=4270"},"modified":"2017-07-05T17:43:35","modified_gmt":"2017-07-05T17:43:35","slug":"functions-of-the-integumentary-system","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-wmopen-biology2\/chapter\/functions-of-the-integumentary-system\/","title":{"raw":"Functions of the Integumentary System","rendered":"Functions of the Integumentary System"},"content":{"raw":"

Describe the different functions of the skin<\/h2>\r\nThe skin and accessory structures perform a variety of essential functions, such as protecting the body from invasion by microorganisms, chemicals, and other environmental factors; preventing dehydration; acting as a sensory organ; modulating body temperature and electrolyte balance; and synthesizing vitamin D. The underlying hypodermis has important roles in storing fats, forming a \u201ccushion\u201d over underlying structures, and providing insulation from cold temperatures.\r\n
\r\n

Learning Objectives<\/h3>\r\n
    \r\n \t
  • Describe the role the integumentary system plays in protection and sensation<\/li>\r\n \t
  • Explain how the skin helps maintain body temperature<\/li>\r\n \t
  • Describe the process of vitamin D synthesis in the body<\/li>\r\n<\/ul>\r\n<\/div>\r\n

    Protection<\/h2>\r\nThe skin protects the body against pathogens and chemicals, minimizes loss or entry of water, and blocks the harmful effects of sunlight.\u00a0It also is the first line of defense against abrasive activity due to contact with grit, microbes, or harmful chemicals.\r\n\r\nThe skin flora, or\u00a0microorganisms which reside on the skin, play an important role in protection. The skin flora can protect the human host by preventing transient pathogenic organisms from colonizing the skin surface, either by competing for nutrients, secreting chemicals against them, or stimulating the skin's immune system.\u00a0Sweat excreted from sweat glands also deters microbes from over-colonizing the skin surface by generating dermicidin, which has antibiotic properties.\u00a0Another factor affecting the growth of pathological bacteria is alkaline conditions. Bacteria are unable to attach effectively to the skin and are more readily shed in alkaline conditions.\r\n\r\nSkin acts as a protective barrier against water loss, due to the presence of layers of keratin and glycolipids in the stratum corneum.\u00a0The cells of the stratum corneum can also absorb water, further aiding in hydration.\r\n

    Sensory Function<\/h2>\r\n[caption id=\"attachment_2858\" align=\"alignright\" width=\"400\"]\"This Figure\u00a01. In this micrograph of a skin cross-section, you can see a Meissner corpuscle (arrow), a type of touch receptor located in a dermal papilla adjacent to the basement membrane and stratum basale of the overlying epidermis. LM \u00d7 100. (credit: \u201cWbensmith\u201d\/Wikimedia Commons)[\/caption]\r\n\r\nThe fact that you can feel an ant crawling on your skin, allowing you to flick it off before it bites, is because the skin, and especially the hairs projecting from hair follicles in the skin, can sense changes in the environment. The hair root plexus surrounding the base of the hair follicle senses a disturbance, and then transmits the information to the central nervous system (brain and spinal cord), which can then respond by activating the skeletal muscles of your eyes to see the ant and the skeletal muscles of the body to act against the ant.\r\n\r\nThe skin acts as a sense organ because the epidermis, dermis, and the hypodermis contain specialized sensory nerve structures that detect touch, surface temperature, and pain. These receptors are more concentrated on the tips of the fingers, which are most sensitive to touch, especially the Meissner corpuscle<\/strong> (tactile corpuscle) (Figure\u00a01), which responds to light touch, and the Pacinian corpuscle<\/strong> (lamellated corpuscle), which responds to vibration. Merkel cells, seen scattered in the stratum basale, are also touch receptors. In addition to these specialized receptors, there are sensory nerves connected to each hair follicle, pain and temperature receptors scattered throughout the skin, and motor nerves innervate the arrector pili muscles and glands. This rich innervation helps us sense our environment and react accordingly.\r\n

    Thermoregulation<\/h2>\r\nBody temperature is primarily regulated by an area in the brain known as the hypothalamus. The hypothalamus sets the body\u2019s temperature and controls it by opening and closing sweat glands and contracting muscles.\r\n\r\nThe integumentary system helps regulate body temperature through its tight association with the sympathetic nervous system, the division of the nervous system involved in our fight-or-flight responses. The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate motor responses.\r\n\r\nRecall that sudoriferous glands, accessory structures to the skin, secrete sweat\u00a0to cool the body when it becomes warm. Even when the body does not appear to be noticeably sweating, approximately 500 mL of sweat (insensible perspiration) are secreted a day. If the body becomes excessively warm due to high temperatures, vigorous activity (Figure\u00a02), or a combination of the two, sweat glands will be stimulated by the sympathetic nervous system to produce large amounts of sweat, as much as 0.7 to 1.5 L per hour for an active person. When the sweat evaporates from the skin surface, the body is cooled as body heat is dissipated.\r\n\r\nIn addition to sweating, arterioles in the dermis dilate so that excess heat carried by the blood can dissipate through the skin and into the surrounding environment (Figure\u00a02). This accounts for the skin redness that many people experience when exercising.\r\n\r\n[caption id=\"attachment_2859\" align=\"aligncenter\" width=\"1024\"]\"Part Figure\u00a02. During strenuous physical activities, such as skiing (a) or running (c), the dermal blood vessels dilate and sweat secretion increases (b). These mechanisms prevent the body from overheating. In contrast, the dermal blood vessels constrict to minimize heat loss in response to low temperatures (b). (credit a: \u201cTrysil\u201d\/flickr; credit c: Ralph Daily)[\/caption]\r\n\r\nWhen body temperatures drop, the arterioles constrict to minimize heat loss, particularly in the ends of the digits and tip of the nose. This reduced circulation can result in the skin taking on a whitish hue. Although the temperature of the skin drops as a result, passive heat loss is prevented, and internal organs and structures remain warm. If the temperature of the skin drops too much (such as environmental temperatures below freezing), the conservation of body core heat can result in the skin actually freezing, a condition called frostbite.\r\n
    \r\n

    Practice Questions<\/h3>\r\nWhy do people sweat excessively when exercising outside on a hot day?\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"666424\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"666424\"]Sweating cools the body when it becomes warm. When the body temperature rises, such as when exercising on a hot day, the dermal blood vessels dilate, and the sweat glands begin to secrete more sweat. The evaporation of the sweat from the surface of the skin cools the body by dissipating heat.\r\n\r\n[\/hidden-answer]\r\n
    \r\n

    Explain your skin\u2019s response to a drop in body core temperature.<\/p>\r\n\r\n<\/div>\r\n

    \r\n
    [practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"916\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"916\"]When the core body temperature drops, the body switches to heat-conservation mode. This can include an inhibition to excessive sweating and a decrease of blood flow to the papillary layers of the skin. This reduction of blood flow helps conserve body heat.[\/hidden-answer]<\/div>\r\n<\/div>\r\n<\/div>\r\n

    Vitamin D Synthesis<\/h2>\r\nThe epidermal layer of human skin synthesizes vitamin D<\/strong> when exposed to UV radiation. In the presence of sunlight, a form of vitamin D3<\/sub> called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys. Vitamin D is essential for normal absorption of calcium and phosphorous, which are required for healthy bones. The absence of sun exposure can lead to a lack of vitamin D in the body, leading to a condition called rickets<\/strong>, a painful condition in children where the bones are misshapen due to a lack of calcium, causing bowleggedness. Elderly individuals who suffer from vitamin D deficiency can develop a condition called osteomalacia, a softening of the bones. In present day society, vitamin D is added as a supplement to many foods, including milk and orange juice, compensating for the need for sun exposure.\r\n\r\nIn addition to its essential role in bone health, vitamin D is essential for general immunity against bacterial, viral, and fungal infections. Recent studies are also finding a link between insufficient vitamin D and cancer.\r\n

    Check Your Understanding<\/strong><\/h2>\r\nAnswer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does\u00a0not<\/strong>\u00a0count toward your grade in the class, and you can retake it an unlimited number of times.\r\n\r\nUse this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/5062","rendered":"

    Describe the different functions of the skin<\/h2>\n

    The skin and accessory structures perform a variety of essential functions, such as protecting the body from invasion by microorganisms, chemicals, and other environmental factors; preventing dehydration; acting as a sensory organ; modulating body temperature and electrolyte balance; and synthesizing vitamin D. The underlying hypodermis has important roles in storing fats, forming a \u201ccushion\u201d over underlying structures, and providing insulation from cold temperatures.<\/p>\n

    \n

    Learning Objectives<\/h3>\n
      \n
    • Describe the role the integumentary system plays in protection and sensation<\/li>\n
    • Explain how the skin helps maintain body temperature<\/li>\n
    • Describe the process of vitamin D synthesis in the body<\/li>\n<\/ul>\n<\/div>\n

      Protection<\/h2>\n

      The skin protects the body against pathogens and chemicals, minimizes loss or entry of water, and blocks the harmful effects of sunlight.\u00a0It also is the first line of defense against abrasive activity due to contact with grit, microbes, or harmful chemicals.<\/p>\n

      The skin flora, or\u00a0microorganisms which reside on the skin, play an important role in protection. The skin flora can protect the human host by preventing transient pathogenic organisms from colonizing the skin surface, either by competing for nutrients, secreting chemicals against them, or stimulating the skin’s immune system.\u00a0Sweat excreted from sweat glands also deters microbes from over-colonizing the skin surface by generating dermicidin, which has antibiotic properties.\u00a0Another factor affecting the growth of pathological bacteria is alkaline conditions. Bacteria are unable to attach effectively to the skin and are more readily shed in alkaline conditions.<\/p>\n

      Skin acts as a protective barrier against water loss, due to the presence of layers of keratin and glycolipids in the stratum corneum.\u00a0The cells of the stratum corneum can also absorb water, further aiding in hydration.<\/p>\n

      Sensory Function<\/h2>\n
      \"This<\/p>\n

      Figure\u00a01. In this micrograph of a skin cross-section, you can see a Meissner corpuscle (arrow), a type of touch receptor located in a dermal papilla adjacent to the basement membrane and stratum basale of the overlying epidermis. LM \u00d7 100. (credit: \u201cWbensmith\u201d\/Wikimedia Commons)<\/p>\n<\/div>\n

      The fact that you can feel an ant crawling on your skin, allowing you to flick it off before it bites, is because the skin, and especially the hairs projecting from hair follicles in the skin, can sense changes in the environment. The hair root plexus surrounding the base of the hair follicle senses a disturbance, and then transmits the information to the central nervous system (brain and spinal cord), which can then respond by activating the skeletal muscles of your eyes to see the ant and the skeletal muscles of the body to act against the ant.<\/p>\n

      The skin acts as a sense organ because the epidermis, dermis, and the hypodermis contain specialized sensory nerve structures that detect touch, surface temperature, and pain. These receptors are more concentrated on the tips of the fingers, which are most sensitive to touch, especially the Meissner corpuscle<\/strong> (tactile corpuscle) (Figure\u00a01), which responds to light touch, and the Pacinian corpuscle<\/strong> (lamellated corpuscle), which responds to vibration. Merkel cells, seen scattered in the stratum basale, are also touch receptors. In addition to these specialized receptors, there are sensory nerves connected to each hair follicle, pain and temperature receptors scattered throughout the skin, and motor nerves innervate the arrector pili muscles and glands. This rich innervation helps us sense our environment and react accordingly.<\/p>\n

      Thermoregulation<\/h2>\n

      Body temperature is primarily regulated by an area in the brain known as the hypothalamus. The hypothalamus sets the body\u2019s temperature and controls it by opening and closing sweat glands and contracting muscles.<\/p>\n

      The integumentary system helps regulate body temperature through its tight association with the sympathetic nervous system, the division of the nervous system involved in our fight-or-flight responses. The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate motor responses.<\/p>\n

      Recall that sudoriferous glands, accessory structures to the skin, secrete sweat\u00a0to cool the body when it becomes warm. Even when the body does not appear to be noticeably sweating, approximately 500 mL of sweat (insensible perspiration) are secreted a day. If the body becomes excessively warm due to high temperatures, vigorous activity (Figure\u00a02), or a combination of the two, sweat glands will be stimulated by the sympathetic nervous system to produce large amounts of sweat, as much as 0.7 to 1.5 L per hour for an active person. When the sweat evaporates from the skin surface, the body is cooled as body heat is dissipated.<\/p>\n

      In addition to sweating, arterioles in the dermis dilate so that excess heat carried by the blood can dissipate through the skin and into the surrounding environment (Figure\u00a02). This accounts for the skin redness that many people experience when exercising.<\/p>\n

      \"Part<\/p>\n

      Figure\u00a02. During strenuous physical activities, such as skiing (a) or running (c), the dermal blood vessels dilate and sweat secretion increases (b). These mechanisms prevent the body from overheating. In contrast, the dermal blood vessels constrict to minimize heat loss in response to low temperatures (b). (credit a: \u201cTrysil\u201d\/flickr; credit c: Ralph Daily)<\/p>\n<\/div>\n

      When body temperatures drop, the arterioles constrict to minimize heat loss, particularly in the ends of the digits and tip of the nose. This reduced circulation can result in the skin taking on a whitish hue. Although the temperature of the skin drops as a result, passive heat loss is prevented, and internal organs and structures remain warm. If the temperature of the skin drops too much (such as environmental temperatures below freezing), the conservation of body core heat can result in the skin actually freezing, a condition called frostbite.<\/p>\n

      \n

      Practice Questions<\/h3>\n

      Why do people sweat excessively when exercising outside on a hot day?<\/p>\n