5-2a Epidermis



5-1 Functions of the SkinThe skin has seven functions:Skin is a covering for the underlying, deeper tissues, protecting them from dehydration, injury, and germ invasion.Skin helps regulate body temperature by controlling the amount of heat loss. Evaporation of water from the skin, in the form of perspiration, helps rid the body of excess heat.Skin helps to manufacture vitamin D. The ultraviolet light on the skin is necessary for the first stages of vitamin D formation.Skin is the site of many nerve endings (Figure 5-1). A square inch of skin contains about 72 feet of nerves and hundreds of receptors.Figure?5-1The skin is well supplied with nerves? Cengage Learning 2014Skin has tissues for the temporary storage of fat, glucose, water, and salts such as sodium chloride. Most of these substances are later absorbed by the blood and transported to other parts of the body.Skin serves to reduce the harmful ultraviolet radiation contained in sunlight.Skin has special properties that permit it to absorb certain drugs and other chemical substances. We can apply drugs locally, as in the case of treating rashes; or we can apply medications that can be absorbed through the skin and have a general effect in the body. An example of this is Nitro-Bid paste, which is used to help dilate blood vessels in the treatment of angina pectoris (chest pain).5-2 Structure of the SkinSkin animationWatch the animation to learn about the largest organ in the body.Volume 90%?? Cengage LearningThe skin consists of two basic layers:The?epidermis?(ep-ih-DER-mis)?or outermost covering is made of epithelial cells with no blood vessels present (avascular).The?dermis?or true skin is made of connective tissue and is vascular.See?Figure 5-2.Figure?5-2A cross section of the skinA, ? Cengage Learning 2014; B, Courtesy of University of Wisconsin Medical School, Madison, WI.5-2a EpidermisThe epidermis consists of four distinct cell types and five layers. The thickness of the epidermis varies: It is thinnest on the eyelids and thickest on the palms of the hands and the soles of the feet. The surface layer (stratum corneum) consists of dead cells rich in keratin.?Keratin?(KER-ah-tin)?is a protein that renders the skin dry and provides a waterproof covering, thus resisting evaporation and preventing excessive water loss. It also serves as a barrier against ultraviolet light, bacteria, abrasions, and some chemicals.The epidermal cells are as follows:Keratinocytes comprise most of the epidermis and produce the protein keratin.Merkel cells are the sensory receptors for touch.Melanocytes?(MEL-ah-noh-sightz)?make the protein?melanin?(MEL-ah-nin), which protects the skin against the ultraviolet rays of the sun.Langerhans cells (not the same as the islets of Langerhans in the pancreas) are macrophages that are effective in the defense of the skin against microorganisms.Following are the epidermal layers from the deepest to the most superficial:The?stratum germinativum?(STRAT-um jer-mih-NAY-tih-vum), or stratum basale, undergoes continuous cell division; it is the deepest epidermal layer. It consists of a layer of cells that are mostly keratinocytes. They grow upward and become part of the more superficial layers, the stratum spinosum. Melanocytes and merkel cells are also found in the germinativum layer.As seen in?Figure 5-2, the lower edge of the stratum germinativum is thrown into ridges. These ridges are known as the?papillae?(pah-PILL-ee)?of the skin. The papillae actually arise from the dermal layer of the skin and push into the stratum germinativum of the epidermis. In the skin of the fingers, soles of the feet, and the palms of the hands, these papillae are quite pronounced; they raise the skin into permanent ridges. These ridges are so arranged that they provide maximum resistance to slipping when grasping and holding objects; thus, they are also referred to as?friction ridges. The ridges form the fingerprint patterns used in identification. Feet contain the same structures and newborn infants are footprinted as a means of identification.The?stratum spinosum?(spye-NOH-sum)?is 8 to 10 cell layers thick. Contained in it are melanocytes, keratinocytes, and Langerhans cells. When seen under a microscope, the cells in this layer look prickly, and thus the name?spinosum, meaning “little spine.”The?stratum granulosum?(gran-yoo-LOH-sum)?is where the keratinization process begins and the cells begin to die. Keratinization is the process whereby the keratinocyte cells change their shape, lose their nucleus, lose most of their water, and become mainly hard protein or keratin.The?stratum lucidum?(LOO-sid-um)?is found only on the palms of the hand and the soles of the feet. The cells in this layer appear clear.The?stratum corneum?(COR-nee-um)?is composed of dead, flat, scalelike keratinized cells, which slough off daily. Complete cell turnover occurs every 28 to 30 days in young adults, while the same process takes 45 to 50 days in elderly adults. This layer is also slightly acidic, which helps in the defense against harmful microorganisms.5-2b Skin ColorThree pigments contribute to skin color: melanin, carotene, and hemoglobin.Melanocytes produce two distinct classes of melanin: pheomelanin, which is red to yellow in color, and eumelanin, which is dark brown to black. People who have light skin generally have a greater proportion of pheomelanin in their skin than those who have dark skin. Both classes of melanin bind to a wide variety of compounds, including some drugs. Because of their affinity for melanin, some drugs make the skin burn more easily (photosensitive). In the elderly, melanin collects in spots, often called “aging” or “liver” spots.The environment can modify skin coloring. Exposure to sunlight may result in a temporary increase of eumelanin, causing a darkened or tanned effect. Prolonged exposure to the ultraviolet rays of sunlight is dangerous because it may lead to the development of skin cancers.Carotene is a yellow to orange pigment found in certain plants. It tends to accumulate in the stratum corneum. The yellowish tinge of the skin of some Asians is due to variations in melanin as well as to carotene. The pinkish color of some fair-skinned people is due to the presence of oxygen in the hemoglobin of the red blood cells circulating through the dermal capillaries.Alterations in skin color may indicate disease conditions or emotional states, as listed in?Table 5-1.Table?5-1Skin Color as Indicator of a Disease ConditionSkin ColorCauseConditionRedness—erythema?(er-ih-THEE-mah)Dilation of capillary networkFever, allergic reaction, inflammation, or embarrassmentBluish tint—cyanosis?(sigh-ah-NOH-sis)?Grayish tint may be present in darker skinned peopleDecrease in oxygen in capillary networkHeart or respiratory diseaseYellow; term?jaundice?is also used to denote yellow coloringAccumulation of bile in capillary networkGallbladder or liver diseasePallorConstriction of capillary network or decrease in red blood cellsEmotional stress or anemia5-2c DermisThe dermis, or corium, is the thicker, inner layer of the skin that lies directly below the epidermis. It is composed of dense connective tissue, collagen tissue bands,?elastic fibers (through which pass numerous blood vessels), muscle fibers, some mast cells and white blood cells, oil and fat glands, and fat cells.The mast cells in the dermis respond to injury, infection, or allergy and produce histamine and heparin. Histamine is released in response to allergens, causing the signs of an allergic reaction, itching, and increased mucus secretions. Heparin is released in response to injury and prevents blood clotting (anticoagulant).The thickness of the dermis varies over different parts of the body. It is, for instance, thicker over the soles of the feet and the palms of the hand. The skin covering the shoulders and back is thinner than that over the palms, but thicker than the skin over the abdomen and thorax.The dermal layer contains many nerve receptors of different types. The sensory nerves end in nerve receptors, which are sensitive to heat, cold, touch, pain, and pressure. The locations of nerve endings vary. The receptors for touch are closer to the epidermis so you can feel someone's touch. However, the pressure receptors are deeper in the dermal layer. This explains why you can sit for a long period before you feel uncomfortable. Nerve endings that sense pain are located under the epidermis and around the hair follicles. These pain receptors are especially numerous on the lower arm, breast, and forehead.Blood vessels in the dermis aid in the regulation of body temperature to maintain homeostasis. When external temperatures increase, blood vessels in the dermis dilate to bring more warmed blood flow to the surface of the body from deeper tissues. On a hot day, the heat brought to the skin's surface can be lost through the process of radiation (transfer of heat from a warm body to a cooler environment), convection (air currents that pick up and transfer heat away from a warm surface), conduction (transfer of heat from a warm object to a cooler object it is in contact with), or evaporation (transfer of heat into body fluids, which are then evaporated from the body surface to the air). Heat loss through these means will cool the body. If the body is exposed to cold for an extended period of time, the blood vessels will constrict to bring warmed blood closer to vital organs to warm and preserve them. This process cannot be maintained for long periods of time.5-2d Subcutaneous or Hypodermal LayerThe subcutaneous or hypodermal layer is not a true part of the integumentary system. It lies under the dermis and sometimes is called superficial fascia. It consists of loose connective tissue and contains about one-half of the body's stored fat. The hypodermal layer attaches the integumentary system to the surface muscles underneath. Injections given in this area are called hypodermic or subcutaneous.5-3 Appendages of the SkinThe appendages of the skin include the hair, nails, sudoriferous (sweat) glands, and sebaceous (oil) glands and their ducts.5-3a HairHairs are distributed over most of the surface area of the body. They are missing from the palms of hands, soles of feet, glans penis, and inner surfaces of the vaginal labia.The length, thickness, type, and color of hair vary with the different body parts and different races. The hairs of the eyelids, for example, are extremely short, whereas hair from the scalp can grow to a considerable length. Facial and pubic hair is quite thick.A hair is composed of a root shaft, the outer cuticle layer, the?cortex, and the inner?medulla. The cuticle consists of a single layer of flat, scalelike, keratinized cells that overlap each other. The cortex consists of elongated, keratinized, nonliving cells. Hair pigment is located in the cortex. In dark hair, the cortex contains pigment granules; as one ages, pigment granules are replaced with air, which gives a gray or white appearance to hair.The?root?is the part of the hair that is implanted in the skin. The?shaft?projects from the skin surface. The root is embedded in an inpocketing of the epidermis called the?hair follicle,?Figure 5-3. Hair varies from straight to curly. The shape of the hair follicle determines the curl of the hair. A round follicle makes straight hair, an oval follicle makes wavy hair, and a flat follicle makes curly hair. Toward the lower end of the hair follicle is a tuft of tissue called the papilla, which extends upward into the hair root. The papilla contains capillaries that nourish the hair follicle cells. This is important because the division of cells in the hair follicle gives rise to a new hair.Figure?5-3The anatomy of an individual hair? Cengage Learning 2014There is a genetic predisposition in some people to a condition known as?alopecia?(al-oh-PEE-shee-ah)?or baldness, which is a permanent hair loss. The normal hair is replaced by a very short hair that is transparent and for practical purposes invisible. Males typically experience more hair loss than women and at a younger age. Treatment for baldness includes medications (topical and oral) and hair transplants.Attached to each hair follicle on the side toward which it slopes is a smooth muscle called the? HYPERLINK "javascript://" arrector pili muscle?(ah-RECK-tor?PYE-lye?). When it is stimulated, as by a sudden chill, it contracts and causes the skin to pucker around the hair. This reaction may be called “goosebumps” or “gooseflesh.”5-3b NailsThe nails are hard structures at the ends of the fingers and toes. They are slightly convex on their upper surfaces and concave on their lower surfaces. A nail is formed in the nail bed or matrix,?Figure 5-4. Here the epidermal cells first appear as elongated cells. These then fuse together to form hard, keratinized plates. Air mixed in the keratin matrix forms the white crescent at the proximal end of each nail called the lunula ) and the white at the free edge of the nail. As long as a nail bed remains intact, a nail will always be formed. Healthy nails are usually pink in color and grow 1 mm per week. Fingernails grow faster than toe-nails, and as we age nails grow more slowly.Figure?5-4Diagram of the fingernail bed? Cengage Learning 2014Some disease conditions may be revealed by the color of a person's nails.ConditionNail ColorLiver diseaseWhite nailsKidney diseaseHalf of nail is pink, half is whiteHeart conditionNail bed is redLung diseaseYellow and thickening nailsAnemiaPale nail bedDiabetesYellowish with a slight blush at the baseHypoxiaBluish in color5-3c Sweat GlandsWhile actual excretion is a minor function of the skin, certain wastes dissolved in perspiration are removed. Perspiration is 99% water with only small quantities of salt and organic materials (waste products).?Sweat glands, also called sudoriferous glands, are distributed over the entire skin surface. They are present in large numbers under the arms, and on the palms of the hands, soles of the feet, and forehead.Sweat glands are tubular, with a coiled base and a tubelike duct that extends to form a pore in the skin, see?Figure 5-2. Perspiration is excreted through the pores. Under the control of the nervous system, these glands may be activated by several factors including heat, pain, fever, and nervousness.The amount of water lost through the skin is almost 500 mL a day, although this varies according to the type of exercise and the environmental temperature. In profuse sweating, a great deal of water may be lost; it is vital to replace the lost water as soon as possible.Ceruminous or wax glands are modifications of the sweat glands. These are found in the ear canals and produce ear wax.5-3d Sebaceous GlandsThe skin is protected by a thick, oily substance known as?sebum?(SEE-bum)?secreted by the?sebaceous glands?(see-BAY-shus)?. Sebum contains amino acids, lactic acids, lipids, salt, and urea. Sebum lubricates the skin, keeping it soft and pliable.5-4 The Integument and Its Relationship to MicroorganismsAn intact skin surface is the best way the body can defend itself against pathogens (disease-producing toxins) and water loss. If skin is especially dry, lotions or creams may prevent cracking.Most of the skin surface is not a favorable place for microbial growth because it is too dry. Microbes live only on moist skin areas where they adhere to and grow on the surfaces of dead cells that compose the outer epidermal layer. The types of microbes found are of the?Staphylococcus?or?Corynebacterium?bacterial species. The other common types found on the skin are?fungi?and?yeasts.*?(See?Chapter 16).Most skin bacteria are associated with the hair follicles or sweat glands, where nutrients are present and the moisture content is high. Underarm perspiration odor is caused by the interaction of bacteria on perspiration. This odor can be minimized or prevented either by decreasing perspiration with antiperspirants or killing the bacteria with deodorant soaps.5-4a HandwashingHandwashing videoWatch the video to learn the proper technique for handwashing.Volume 90%?? Cengage LearningThe number one way to prevent the spread of disease is by handwashing. Wash hands in running water, using soap and friction, Be sure to scrub the backs of hands, between the fingers, and under the nails. Rub hands for at least 20 seconds (time yourself by singing “Happy Birthday” silently to yourself two times). Rinse and dry hands using a paper towel or air dryer. If you are in contact with infectious material, the washing time should be from 2 to 4 minutes. If you may come in contact with blood, infectious material, or any body secretions, first wash the hands and apply gloves before exposure. After exposure, remove the gloves, and wash the hands again.If soap and water are not available, use an alcohol-based hand sanitizer that contains at least 60% alcohol. Sanitizers quickly reduce the number of germs on the hands in some situations but do not eliminate all types of germs.5-8 BurnsBurns animationWatch the animation to learn about first, second and third degree burns.Volume 90%?? Cengage LearningBurns are a traumatic injury that results from exposure to radiation from the sun (sunburn), a heat lamp, or contact with boiling water, steam, fire, chemicals, or electricity. When the skin is burned, dehydration and infection may occur—either condition can be life threatening. The?rule of nines?measures the percent of the body burned: The body is divided into 11 areas and each area accounts for 9% of the total body surface. For example, each arm is 4.5%; the perineal area accounts for 1%,?Figure 5-8.Figure?5-8The rule of nines is used to calculate percentage of body surface burned? Cengage Learning 2014Burns are usually referred to as first, second, or third degree, depending on the skin layers affected and the symptoms,?Figure 5-9.Figure?5-9Burns are usually referred to as (A) first degree (superficial), (B) second degree (partial thickness), or (C) third degree (full thickness)A, B, and C Photos courtesy of The Phoenix Society for Burn Survivors, Inc.; ? Cengage Learning 2014.Researchers are developing methods of treating burns that take advantage of stem cell therapy. HYPERLINK "javascript://" First-degree?or?superficial burns?involve only the epidermis. Sunburns are often considered to be first-degree burns. Symptoms are redness, swelling, and pain. Treatment consists of the application of cold water. Healing usually occurs within one week.Second-degree?or?partial-thickness burns?may involve the epidermis and dermis. Symptoms include pain, swelling, redness, and blistering. The skin may also be exposed to infection. Treatment may include pain medication and dry sterile dressings applied to open skin areas. Healing generally occurs within 2 weeks.Third-degree?or?full-thickness burns?involve complete destruction of the epidermis, dermis, and subcutaneous layers. Symptoms include loss of skin,?eschar?(ah-BRAY-zhun)?(blackened skin), yet possibly no pain since nerve endings may have also been affected by the burns. This may be a life-threatening situation, depending on the amount of skin damaged and fluid and blood plasma lost. The person requires immediate hospitalization. Treatment consists of prevention of infection, contracture (a condition of shortening and hardening of tissue often leading to deformity and rigidity of joints), and fluid replacement. Skin grafting is done as soon as possible.5-9 Skin LesionsThe health care professional should be familiar with the different types of skin disorders or lesions. Sometimes skin lesions indicate only an outer skin disorder. An abrasion is an injury in which superficial layers of the skin are scraped or rubbed away. A fissure is a groove or crack-like break in the skin. A laceration is a torn or jagged wound.5-9a Pressure Ulcer/DecubitusPressure ulcers, also known as?decubitus ulcers?(de-KEW-bih-tus)?or bedsores, are preventable and are a primary concern of health care professionals. Decubitus ulcers occur when a person is constantly sitting or?lying in the same position without shifting his or her weight. Any area of tissue that lies over a bone is much more likely to develop a decubitus ulcer. These areas include the spine, coccyx, hips, elbows, and heels. The constant pressure against the area causes a decrease in the blood supply and thus the tissue begins to decay. These ulcers are classified in stages according to their severity:Stage I?involves surface reddening, but the skin is unbroken. Treatment is to alleviate the pressure.Stage II?is characterized by blistered areas that are either broken or unbroken; the surrounding area is red and irritated. Treatment is to protect and clean the area and alleviate the pressure.Stage III?presents with skin breaks through all layers of skin. It becomes a primary site for infection. Medical treatment is necessary to treat and prevent infection and promote healing.Stage IV?ulcers have an ulcerated area that extends through skin and involves underlying muscles, tendons, and bones. This can produce a life-threatening situation. Treatment is with surgical removal of necrotic (dead) or decayed areas and antibiotics.The best treatment for decubitus ulcers is prevention. Frequent turning and relief of pressure on bony prominences is essential. If the person is at home, family members must be educated on how to prevent the disorder.Table 5-2?and?Figure 5-10?describe some of the different types of skin lesions, their characteristics, and their dimensions.Table?5-2Different Types of Skin Lesions, Their Characteristics, Sizes, and Examples of EachType of Skin LesionCharacteristicsSizeExample(s)Bulla (large blister)Fluid-filled areaGreater than 10 mm acrossA large blisterMaculeFlat area usually distinguished from its surrounding skin by its change in colorSmaller than 1 cmFrecklePetechiaNoduleElevated solid area, deeper and firmer than a papuleGreater than 10 mm acrossWartPapuleElevated solid area5 mm or less acrossElevated nevusPustuleDiscrete, pus-filled raised areaVarying sizeAcneUlcerA deep loss of skin surface that may extend into the dermis that can bleed periodically and scarVaries in sizeVenous stasis ulcerDecubitusTumorSolid abnormal mass of cells that may extend deep through cutaneous tissueLarger than 1 to 2 cmBenign (harmless) epidermal tumorBasal cell carcinoma (rarely metastasizing)Vesicle small blisterFluid-filled raised area10 mm or less acrossChickenpoxHerpes simplexHives (wheal)Itchy, temporarily elevated area with an irregular shape formed as a result of localized skin edemaVaries in sizeHivesInsect bites??Cengage Learning?2014Figure?5-10Different types of skin lesions? Cengage Learning 2014Career Profile?5-1PhysiciansPhysicians diagnose illnesses and prescribe and administer treatments for people suffering from illness and disease. Physicians examine patients, obtain medical histories, and order, perform, and interpret diagnostic tests. They counsel patients on hygiene, diet, and preventive health care.Two types of physicians are the doctor of medicine (M.D.), and the doctor of osteopathy (D.O.). Both physicians may use all methods of treatment. Doctors of osteopathy place special emphasis on the body's musculoskeletal system and preventive and holistic medicine.Some physicians are primary care physicians who practice general and family medicine. Some are specialists who are experts in their medical field such as dermatology, cardiology, or pediatrics.Most physicians work long, irregular hours. Increasingly, they practice in groups or health care organizations. To become a physician requires 4 years of undergraduate study, 4 years of medical school, and 3 to 8 years of internship and residency, depending on the specialization. Physicians must pass their medical boards to obtain a license to practice. Formal education and training requirements are among the longest of any occupation, but the earnings are among the highest.??Cengage Learning?2014One BodyHow the Integumentary System Interacts With Other Body SystemsSkeletal SystemActs as a protective covering for bones.The ultraviolet rays of sun and skin are precursors to vitamin D, which is needed for absorption of calcium and phosphorus for bones.Muscular SystemProvides protective covering for muscles.Provides the vitamin D necessary for muscle contraction.Nervous SystemProvides a protective covering for the nervous system.The skin has sensory receptors for pain, touch, pressure, and temperature.Endocrine SystemProtects the glands.Stores fat necessary for production of hormones.Circulatory SystemProvides a protective covering for the capillary network.Dilation and constriction of the capillary network regulates body temperature.Mast cells help in production of heparin.Lymphatic SystemProvides a protective covering for lymph vessels.Acts as a waterproof, intact covering to protect against infection.Macrophages help activate the immune system.Respiratory SystemProvides a protective covering for organs of respiration.Hair on skin guards the entrance to the nasal cavity.Digestive SystemActs as a protective covering for the organs of digestion.Provides the vitamin D necessary for absorption of calcium and phosphorus.Urinary SystemProvides a protective covering for the organs of the urinary system.Helps excrete waste products through sweat glands.Reproductive SystemProvides a protective covering for the organs of reproduction.Sensory receptors in genitalia stimulate sexual interest.??Cengage Learning?2014Medical Terminologyalopecbaldness-iaabnormal conditionalopec/iaabnormal condition of baldnessa-withoutvascullittle blood vessels-arpertaining toa/vascul/arbeing without little blood vesselsdecubitbedsore-uspresence ofdecubit/uspresence of bedsore, pressure soredermatskin-itisinflammationdermat/itisinflammation of the skinepi-uponepi/dermisupon the skin; top layer of skinhyper-above normal-thermiaheathyper/thermiaabove normal heathypo-belowhypo/thermiabelow normal heatmelanblack-omatumormelan/omatumor of blackness, usually malignantpapillpimple-apresence ofpapill/apresence of pimplesebacgrease or oil-ouspertaining tosebac/e/ouspertaining to oil glandsstratumlayercorneumhornystratum corneumhorny layer of skin ................
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