Anatomy Physiology Chapter 7 Skin and Its Appendages

Introduction Skin (integument) is body’s largest organ Skin measures approximately 1. 6 to 1.

Structure of the Skin classified as cutaneous membrane Two primary layers—epidermis and dermis; joined

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. ,

Structure of the Skin Epidermis Cell types (Figure 7 -4) Keratinocytes—constitute over 90% of

Structure of the Skin Epidermis (cont) Cell layers Stratum basale (base layer)—single layer of

Structure of the Skin Cell layers Stratum granulosum (granular layer)— cells arranged in two

Structure of the Skin Epidermis (cont) Epidermal growth and repair Turnover or regeneration time

Structure of the Skin Epidermal growth and repair (cont) Shortened turnover time will increase

Structure of the Skin Dermopidermal junction (DEJ) A basement membrane, with unique fibrous elements,

Structure of the Skin Dermis Sometimes called “true skin”—much thicker than the epidermis and

Structure of the Skin Dermis (cont) Contains various structures Arrector pili muscles and hair

Structure of the Skin Dermis (cont) Layers of dermis Papillary layer—composed of dermal papillae

Structure of the Skin Dermis (cont) Dermal growth and repair The dermis does not

Structure of the Skin Hypodermis Also called the subcutaneous layer or superficial fascia Located

Skin Color Melanin Basic determinant is quantity, type, distribution of melanin Types of melanin

Skin Color Melanin (cont) Melanin formed from tyrosine by melanocytes (Figure 7 -8) Melanocytes

Skin Color Melanin (cont) Process regulated by tyrosinase, exposure to sunlight (UV radiation), and

Skin Color Other Pigments Beta-carotene (group of yellowish pigments from food) can also contribute

Skin Color Other Pigments (cont) Hemoglobin—color changes also occur as a result of changes

Functions of the Skin (Table 7 -2) Protection Physical barrier to microorganisms Barrier to

Functions of the Skin Surface film Emulsified protective barrier formed by mixing of residue

Functions of the Skin Surface film (cont) Chemical composition From epithelial elements—amino acids, sterols,

Functions of the Skin Sensation Somatic sensory receptors detect stimuli that permit us to

Functions of the Skin Hormone (vitamin D) production (Figure 7 -14) Exposure of skin

Functions of the Skin Immunity Phagocytic cells destroy bacteria Epidermal dendritic cells trigger helpful

Functions of the Skin Homeostasis of body temperature (cont) Heat production By metabolism of

Functions of the Skin Homeostasis of body temperature (cont) Heat loss—approximately 80% of heat

Functions of the Skin Homeostasis of body temperature (cont) Heat loss (cont) Radiation—transfer of

Functions of the Skin Homeostasis of body temperature (cont) Homeostatic regulation of heat loss

Appendages of the Skin Hair (Figure 7 -17) Development of hair Distribution—over entire body

Appendages of the Skin Hair (cont) Development of hair (cont) Papilla—cluster of capillaries under

Appendages of the Skin Hair (cont) Appearance of hair Color—result of different amounts, distribution,

Appendages of the Skin Nails (Figure 7 -20) Consist of epidermal cells converted to

Appendages of the Skin Nails (cont) Nail bed—layer of epithelium under nail body; contains

Appendages of the Skin glands (Figure 7 -23) Two types of sweat glands Eccrine

Appendages of the Skin Two types of sweat glands (cont) Apocrine glands Located deep

Appendages of the Skin glands (cont) Sebaceous glands Secrete sebum—oily substance that keeps hair

Appendages of the Skin glands (cont) Ceruminous glands Modified apocrine sweat glands Simple, coiled,

Cycle of Life: Skin Children Skin is smooth, unwrinkled, and characterized by elasticity and

Cycle of Life: Skin Adults Development and activation of sebaceous and sweat glands Increased

Cycle of Life: Skin Old age Decreased sebaceous and sweat gland activity Wrinkling (Figure

The Big Picture: Skin and the Whole Body Skin is a major component of

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Introduction Skin (integument) is body’s largest organ Skin measures approximately 1. 6 to 1. 8 m 2 in average-sized adult Integumentary system describes the skin and its appendages—the hair, nails, and skin glands Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 2

Structure of the Skin classified as cutaneous membrane Two primary layers—epidermis and dermis; joined by dermoepidermal junction (Figures 7 -1 and 7 -2) Hypodermis lies beneath dermis Thin and thick skin (Figure 7 -3) “Thin skin” —covers most of body surface (1 to 3 mm thick); has hair and smooth surface “Thick skin”—soles and palms (4 to 5 mm thick); ridged surface with no hair Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 3

Structure of the Skin Epidermis Cell types (Figure 7 -4) Keratinocytes—constitute over 90% of cells present; principal structural element of the outer skin; sometimes called corneocytes after they are fully keratinized Melanocytes—pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet light Epidermal dendritic cells—branched antigen-presenting cells (APCs); they play a role in immune response; also called Langerhans cells Tactile epithelial cells (Merkel cells)—attach to sensory nerve endings to form “light touch” receptors Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 7

Structure of the Skin Epidermis (cont) Cell layers Stratum basale (base layer)—single layer of columnar cells; only these cells undergo mitosis and then migrate through the other layers until they are shed; stratum germinativum (growth layer) is another name for stratum basale (or stratum spinosum and stratum basale together) Stratum spinosum (spiny layer)—cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNA Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 9

Structure of the Skin Cell layers Stratum granulosum (granular layer)— cells arranged in two to four layers and filled with keratohyalin granules; contain high levels of lysosomal enzymes Stratum lucidum (clear layer)—cells filled with keratin precursor called eleidin; absent in thin skin Stratum corneum (horny layer)—most superficial layer; dead cells filled with keratin (barrier area) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 10

Structure of the Skin Epidermis (cont) Epidermal growth and repair Turnover or regeneration time refers to time required for epidermal cells to form in the stratum basale and migrate to the skin surface—about 35 days Several hormones support normal growth and repair of the epidermis: epidermal growth factor (EGF), insulinlike growth factor 1 (EGF-1), and growth hormone (GH) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 11

Structure of the Skin Epidermal growth and repair (cont) Shortened turnover time will increase thickness of the stratum corneum and result in callus formation Normally 10% to 12% of all cells in stratum basale enter mitosis daily Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes is called an epidermal proliferating unit, or EPU Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 12

Structure of the Skin Dermopidermal junction (DEJ) A basement membrane, with unique fibrous elements, and a polysaccharide gel serve to “glue” the epidermis to the dermis below The junction serves as a partial barrier to the passage of some cells and large molecules Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 13

Structure of the Skin Dermis Sometimes called “true skin”—much thicker than the epidermis and lies beneath it Gives strength to the skin Serves as a reservoir storage area for water and electrolytes Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 14

Structure of the Skin Dermis (cont) Contains various structures Arrector pili muscles and hair follicles (Figure 7 -5) Sensory receptors (Figure 7 -6) Sweat and sebaceous glands Blood vessels Rich vascular supply plays a critical role in temperature regulation Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 15

Structure of the Skin Dermis (cont) Layers of dermis Papillary layer—composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers; contains the dermoepidermal junction; forms a unique pattern that gives individual fingerprints Reticular layer—contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processed from animal skin, produces leather Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 18

Structure of the Skin Dermis (cont) Dermal growth and repair The dermis does not continually shed and regenerate itself as does the epidermis During wound healing, fibroblasts begin forming an unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar Cleavage lines (Figure 7 -7)—patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 19

Structure of the Skin Hypodermis Also called the subcutaneous layer or superficial fascia Located deep to the dermis; forms connection between skin and other structures Not part of the skin Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 21

Skin Color Melanin Basic determinant is quantity, type, distribution of melanin Types of melanin Eumelanin—group of dark brown (almost black) melanins Pheomelanin—group of reddish and orange melanins Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 22

Skin Color Melanin (cont) Melanin formed from tyrosine by melanocytes (Figure 7 -8) Melanocytes release melanin in packets called melanosomes Melanosomes are ingested by surrounding keratinocytes and form a cap over the nucleus Albinism—congenital absence of melanin Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 23

Skin Color Melanin (cont) Process regulated by tyrosinase, exposure to sunlight (UV radiation), and certain hormones, including melanocortins (ACTH, a-MSH) and ET-1 (Figures 7 -9 and 7 -10) Cumulative effects of UV exposure may produce age spots (Figure 7 -11) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 25

Skin Color Other Pigments Beta-carotene (group of yellowish pigments from food) can also contribute to skin color Lipofuscin—accumulates in cells that have ceased mitosis in aging skin, producing brown-yellow age spots Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 29

Skin Color Other Pigments (cont) Hemoglobin—color changes also occur as a result of changes in blood flow Redder skin color when blood flow to skin increases Cyanosis—bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide (Figure 7 -12) Bruising can cause a rainbow of different colors to appear in the skin (Figure 7 -13) Other pigments—from cosmetics, tattoos, bile pigments in jaundice (Box 7 -4) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 30

Functions of the Skin (Table 7 -2) Protection Physical barrier to microorganisms Barrier to chemical hazards Reduces potential for mechanical trauma Prevents dehydration Protects against excess UV exposure (melanin function) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 33

Functions of the Skin Surface film Emulsified protective barrier formed by mixing of residue and secretions of sweat and sebaceous glands with sloughed epithelial cells from skin surface; shedding of epithelial elements is called desquamation Functions Antibacterial, antifungal activity Lubrication Hydration of skin surface Buffer of caustic irritants Blockade of toxic agents Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 34

Functions of the Skin Surface film (cont) Chemical composition From epithelial elements—amino acids, sterols, and complex phospholipids From sebum—fatty acids, triglycerides, and waxes From sweat—water, ammonia, urea, and lactic acid and uric acid Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 35

Functions of the Skin Sensation Somatic sensory receptors detect stimuli that permit us to detect pressure, touch, temperature, pain, and other general senses Flexibility Skin acts as a sophisticated sense organ Skin is supple and elastic, thus permitting change in body contours without injury Excretion Water Urea/ammonia/uric acid Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 36

Functions of the Skin Hormone (vitamin D) production (Figure 7 -14) Exposure of skin to UV light converts 7 dehydrocholesterol to cholecalciferol—a precursor to vitamin D Blood transports precursor to liver and kidneys where vitamin D is produced Process and end result fulfill the necessary steps required for vitamin D to be classified as a hormone Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 37

Functions of the Skin Immunity Phagocytic cells destroy bacteria Epidermal dendritic cells trigger helpful immune reaction working with “helper T cells” Homeostasis of body temperature To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 39

Functions of the Skin Homeostasis of body temperature (cont) Heat production By metabolism of foods in skeletal muscles and liver Chief determinant of heat production is the amount of muscular work being performed Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 40

Functions of the Skin Homeostasis of body temperature (cont) Heat loss—approximately 80% of heat loss occurs through the skin; remaining 20% occurs through the mucosa of the respiratory, digestive, and urinary tracts (Figure 7 -15) Evaporation—to evaporate any fluid, heat energy must be expended; this method of heat loss is especially important at high environmental temperatures when it is the only method by which heat can be lost from the skin Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 41

Functions of the Skin Homeostasis of body temperature (cont) Heat loss (cont) Radiation—transfer of heat from one object to another without actual contact; important method of heat loss in cool environmental temperatures Conduction—transfer of heat to any substance actually in contact with the body; accounts for relatively small amounts of heat loss Convection—transfer of heat away from a surface by movement of air; usually accounts for a small amount of heat loss Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 43

Functions of the Skin Homeostasis of body temperature (cont) Homeostatic regulation of heat loss (Figure 7 -16) Heat loss by the skin is controlled by a negative feedback loop Receptors in the hypothalamus monitor the body’s internal temperature If body temperature is increased, the hypothalamus sends a nervous signal to the sweat glands and blood vessels of the skin The hypothalamus continues to act until the body’s temperature returns to normal Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 44

Appendages of the Skin Hair (Figure 7 -17) Development of hair Distribution—over entire body except palms of hands and soles of feet and a few other small areas Fine and soft hair coat existing before birth called lanugo Coarse pubic and axillary hair that develops at puberty called terminal hair Hair follicles and hair develop from epidermis; mitosis of cells of germinal matrix forms hairs Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 46

Appendages of the Skin Hair (cont) Development of hair (cont) Papilla—cluster of capillaries under germinal matrix Root—part of hair embedded in follicle in dermis Shaft—visible part of hair Medulla—inner core of hair; cortex— outer portion Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 48

Appendages of the Skin Hair (cont) Appearance of hair Color—result of different amounts, distribution, types of melanin in cortex of hair (Figure 7 -18) Growth—hair growth and rest periods alternate; hair on head averages 5 inches of growth per year Sebaceous glands—attach to and secrete sebum (skin oil) into follicle Male pattern baldness (androgenic alopecia) results from combination of genetic tendency and male sex hormones (Figure 7 -19) Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 49

Appendages of the Skin Nails (Figure 7 -20) Consist of epidermal cells converted to hard keratin Nail body—visible part of each nail Root—part of nail in groove hidden by fold of skin, the cuticle Lunula—moon-shaped white area nearest root Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 52

Appendages of the Skin Nails (cont) Nail bed—layer of epithelium under nail body; contains abundant blood vessels Appears pink under translucent nails Nails may have pigmented streaks (Figure 7 -21) Separation of a nail from the nail bed is called onycholysis (Figure 7 -22) Growth—nails grow by mitosis of cells in statum basale beneath the lunula; average growth about 0. 5 mm per week, or slightly over 1 inch per year Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 54

Appendages of the Skin glands (Figure 7 -23) Two types of sweat glands Eccrine glands Most numerous sweat glands; quite small Distributed over total body surface with exception of a few small areas Simple, coiled, tubular glands Function throughout life Secrete perspiration, or sweat; eliminate wastes and help maintain a constant core temperature Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 57

Appendages of the Skin Two types of sweat glands (cont) Apocrine glands Located deep in subcutaneous layer Limited distribution—axilla, areola of breast, and around anus Large (often more than 5 mm in diameter) Simple, branched, tubular glands Begin to function at puberty Secretion shows cyclic changes in female with menstrual cycle Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 59

Appendages of the Skin glands (cont) Sebaceous glands Secrete sebum—oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from skin Lipid components have antifungal activity Simple, branched glands Found in dermis except in palms and soles Secretion increases in adolescence; may lead to formation of pimples and blackheads Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 60

Appendages of the Skin glands (cont) Ceruminous glands Modified apocrine sweat glands Simple, coiled, tubular glands Empty contents into external ear canal alone or with sebaceous glands Mixed secretions of sebaceous and ceruminous glands called cerumen (wax) Function of cerumen to protect area from dehydration; excess secretion cause blockage of ear canal and loss of hearing Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 61

Cycle of Life: Skin Children Skin is smooth, unwrinkled, and characterized by elasticity and flexibility Few sweat glands Rapid healing Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 62

Cycle of Life: Skin Adults Development and activation of sebaceous and sweat glands Increased sweat production; can result in body odor Increased sebum production; can result in acne Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 63

Cycle of Life: Skin Old age Decreased sebaceous and sweat gland activity Wrinkling (Figure 7 -24) Decrease in body's ability to cool itself Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 64

The Big Picture: Skin and the Whole Body Skin is a major component of the body’s structural framework Skin defines the internal environment of the body Primary functions are support and protection Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc. , an affiliate of Elsevier Inc. 65