Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 6 Skin and its Appendages

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 2 Introduction  Skin (integument) is body’s largest organ  Approximately 1.6 to 1.9 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 © 2007, 2003 by Mosby, Inc.Slide 3 Structure of the Skin  Skin classified as a cutaneous membrane  Two primary layers—epidermis and dermis; joined by dermal-epidermal junction (Figures 6-1 and 6-2)  Hypodermis lies beneath dermis

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 4 Structure of the Skin  Thin and thick skin (Figure 6-3)  “Thin skin”—covers most of body surface (1 to 3 mm thick)  “Thick skin”—soles and palms (4 to 5 mm thick)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 5 Structure of the Skin  Epidermis  Cell types Keratinocytes—constitute over 90% of cells present; principal structural element of the outer skin Keratinocytes—constitute over 90% of cells present; principal structural element of the outer skin Melanocytes—pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet light Melanocytes—pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet light Langerhans cells—dendritic (branched) antigen- presenting cells (APCs), they play a role in immune response Langerhans cells—dendritic (branched) antigen- presenting cells (APCs), they play a role in immune response

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 6 Structure of the Skin  Epidermis (cont.)  Cell layers Stratum germinativum (growth layer)—describes the stratum spinosum and stratum basale together Stratum germinativum (growth layer)—describes the stratum spinosum and stratum basale together  Stratum basale (base layer)—single layer of columnar cells; only these cells undergo mitosis, then migrate through the other layers until they are shed  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 © 2007, 2003 by Mosby, Inc.Slide 7 Structure of the Skin  Cell layers (cont.) Stratum granulosum (granular layer)—cells arranged in two to four layers and filled with keratohyalin granules; contain high levels of lysosomal enzymes 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 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) Stratum corneum (horny layer)—most superficial layer; dead cells filled with keratin (barrier area)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 8 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 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 Shortened turnover time will increase the thickness of the stratum corneum and result in callus formation Shortened turnover time will increase the thickness of the stratum corneum and result in callus formation Normally 10% to 12% of all cells in stratum basale enter mitosis daily 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 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 © 2007, 2003 by Mosby, Inc.Slide 9 Structure of the Skin  Dermal-epidermal junction  A definite basement membrane, specialized 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 © 2007, 2003 by Mosby, Inc.Slide 10 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 area for storage of water and electrolytes

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 11 Structure of the Skin  Dermis (cont.)  Contains various structures: Arrector pili muscles and hair follicles (Figure 6-4) Arrector pili muscles and hair follicles (Figure 6-4) Sensory receptors (Figure 6-5) Sensory receptors (Figure 6-5) Sweat and sebaceous glands Sweat and sebaceous glands Blood vessels Blood vessels  Rich vascular supply plays a critical role in temperature regulation

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 12 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 dermal-epidermal junction; forms a unique pattern that gives individual fingerprints Papillary layer—composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers; contains the dermal-epidermal 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 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 © 2007, 2003 by Mosby, Inc.Slide 13 Structure of the Skin  Dermis (cont.)  Dermal growth and repair The dermis does not continually shed and regenerate itself as does the epidermis The dermis does not continually shed and regenerate itself as does the epidermis During wound healing, the fibroblasts begin forming an unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar During wound healing, the 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 6-6)—patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines Cleavage lines (Figure 6-6)—patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 14 Structure of the Skin  Hypodermis  Also called subcutaneous layer or superficial fascia  Deep to the dermis, forming connection between the skin and other structures  Not part of the skin

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 15 Skin Color  Melanin  Basic determinant of skin color is quantity, type, and distribution of melanin  Types of melanin Eumelanin—group of dark brown (almost black) melanins Eumelanin—group of dark brown (almost black) melanins Pheomelanin—group of reddish and orange melanins Pheomelanin—group of reddish and orange melanins

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 16 Skin Color  Melanin (cont.)  Melanin formed from tyrosine by melanocytes (Figure 6-7) Melanocytes release melanin in packets called melanosomes Melanocytes release melanin in packets called melanosomes Melanosomes are ingested by surrounding keratinocytes and form a cap over the nucleus Melanosomes are ingested by surrounding keratinocytes and form a cap over the nucleus  Albinism—congenital absence of melanin  Process regulated by tyrosinase, exposure to sunlight (UV radiation), and certain hormones including ACTH (Figure 6-8)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 17 Skin Color  Other pigments  Beta carotene (group of yellowish pigments from food) can also contribute to skin color  Hemoglobin—color changes also occur as a result of changes in blood flow Redder skin color when blood flow to skin increases 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 6-9) Cyanosis—bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide (Figure 6-9) Bruising can cause a rainbow of different colors to appear in the skin (Figure 6-10) Bruising can cause a rainbow of different colors to appear in the skin (Figure 6-10)  Other pigments—from cosmetics, tattoos, and bile pigments in jaundice (Box 6-3)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 18 Functions of the Skin (Table 6-2)  Protection  Physical barrier to microorganisms  Barrier to chemical hazards  Reduces potential for mechanical trauma  Prevents dehydration  Protects (via melanin) excess UV exposure

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 19 Functions of the Skin  Protection (cont.)  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 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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 20 Functions of the Skin  Surface film (cont.) Functions Functions  Antibacterial, antifungal activity  Lubrication  Hydration of skin surface  Buffer of caustic irritants  Blockade of toxic agents

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 21 Functions of the Skin  Surface film (cont.) Chemical composition Chemical composition  From epithelial elements—amino acids, sterols, and complex phospholipids  From sebum—fatty acids, triglycerides, and waxes  From sweat—water and ammonia, urea, and lactic acid and uric acid

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 22 Functions of the Skin  Sensation  Skin acts as a sophisticated sense organ  Somatic sensory receptors detect stimuli that permit us to detect pressure, touch, temperature, pain, and other general sensations

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 23 Functions of the Skin  Flexibility  Skin is supple and elastic, thus permitting change in body contours without injury  Excretion  Water  Urea/ammonia/uric acid

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 24 Functions of the Skin  Hormone (Vitamin D) production (Figure 6-11)  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 © 2007, 2003 by Mosby, Inc.Slide 25 Functions of the Skin  Immunity  Phagocytic cells destroy bacteria  Langerhans cells trigger helpful immune reaction working with “helper T cells”

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 26 Functions of the Skin  Homeostasis of body temperatures  To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process  Heat production By metabolism of foods in skeletal muscles and liver By metabolism of foods in skeletal muscles and liver Chief determinant of heat production is the amount of muscular work being performed Chief determinant of heat production is the amount of muscular work being performed

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 27 Functions of the Skin  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 6-12) 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 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 Radiation—transfer of heat from one object to another without actual contact; important method of heat loss in cool environmental temperatures Radiation—transfer of heat from one object to another without actual contact; important method of heat loss in cool environmental temperatures

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 28 Functions of the Skin  Heat loss (cont.) Conduction—transfer of heat to any substance actually in contact with the body; accounts for relatively small amounts of heat loss 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 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 © 2007, 2003 by Mosby, Inc.Slide 29 Functions of the Skin  Homeostatic regulation of heat loss (Figure 6-13) Heat loss by the skin is controlled by a negative feedback loop Heat loss by the skin is controlled by a negative feedback loop Receptors in the hypothalamus monitor the body’s internal temperature Receptors in the hypothalamus monitor the body’s internal temperature If the body temperature is increased, the hypothalamus sends a nervous signal to the sweat glands and blood vessels of the skin If the 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 The hypothalamus continues to act until the body’s temperature returns to normal

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 30 Appendages of the Skin  Hair (Figure 6-14)  Development of hair Distribution—over entire body except palms of hands and soles of feet and a few other small areas Distribution—over entire body except palms of hands and soles of feet and a few other small areas Fine and soft hair coat present before birth called lanugo Fine and soft hair coat present before birth called lanugo Coarse pubic and axillary hair that develops at puberty called terminal hair Coarse pubic and axillary hair that develops at puberty called terminal hair

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 31 Appendages of the Skin  Hair (cont.)  Development of hair (cont.) Hair follicles and hair develop from epidermis; stratum germinativum forms innermost layer of follicle and germinal matrix; mitosis of cells of germinal matrix forms hairs Hair follicles and hair develop from epidermis; stratum germinativum forms innermost layer of follicle and germinal matrix; mitosis of cells of germinal matrix forms hairs Papilla—cluster of capillaries under germinal matrix Papilla—cluster of capillaries under germinal matrix Root—part of hair embedded in follicle in dermis Root—part of hair embedded in follicle in dermis Shaft—visible part of hair Shaft—visible part of hair Medulla—inner core of hair; cortex—outer portion Medulla—inner core of hair; cortex—outer portion

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 32 Appendages of the Skin  Hair (cont.)  Appearance of hair Color—result of different amounts, distribution, types of melanin in cortex of hair (Figure 6-15) Color—result of different amounts, distribution, types of melanin in cortex of hair (Figure 6-15) Growth—hair growth and rest periods alternate; hair on head averages 5 inches of growth per year 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 Sebaceous glands—attach to and secrete sebum (skin oil) into follicle Male pattern baldness results from combination of genetic tendency and male sex hormones (Figure 6-16) Male pattern baldness results from combination of genetic tendency and male sex hormones (Figure 6-16)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 33 Appendages of the Skin  Nails (Figure 6-17)  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 © 2007, 2003 by Mosby, Inc.Slide 34 Appendages of the Skin  Nails (cont.)  Nail bed—layer of epithelium under nail body; contains abundant blood vessels Appears pink under translucent nails Appears pink under translucent nails Nails may have pigmented streaks (Figure 6-18) Nails may have pigmented streaks (Figure 6-18) Separation of nail from nail bed is called onycholysis (Figure 6-19) Separation of nail from nail bed is called onycholysis (Figure 6-19)  Growth—nails grow by mitosis of cells in stratum germinativum beneath the lunula; average growth about 0.5 mm per week, or slightly over 1 inch per year

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 35 Appendages of the Skin  Skin glands (Figure 6-20)  Two types of sweat glands: Eccrine 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 © 2007, 2003 by Mosby, Inc.Slide 36 Appendages of the Skin  Two types of sweat glands (cont.): Apocrine glands 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 © 2007, 2003 by Mosby, Inc.Slide 37 Appendages of the Skin  Skin glands (cont.)  Sebaceous glands Secrete sebum—oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from the skin Secrete sebum—oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from the skin Lipid components have antifungal activity Lipid components have antifungal activity Simple, branched glands Simple, branched glands Found in dermis except in palms and soles Found in dermis except in palms and soles Secretion increases in adolescence; may lead to formation of pimples and blackheads Secretion increases in adolescence; may lead to formation of pimples and blackheads

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 38 Appendages of the Skin  Skin glands (cont.)  Ceruminous glands Modified apocrine sweat glands Modified apocrine sweat glands Simple, coiled, tubular glands Simple, coiled, tubular glands Empty contents into external ear canal alone or with sebaceous glands Empty contents into external ear canal alone or with sebaceous glands Mixed secretions of sebaceous and ceruminous glands called cerumen (wax) Mixed secretions of sebaceous and ceruminous glands called cerumen (wax) Function of cerumen to protect area from dehydration; excess secretion can cause blockage of ear canal and loss of hearing Function of cerumen to protect area from dehydration; excess secretion can cause blockage of ear canal and loss of hearing

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 39 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 © 2007, 2003 by Mosby, Inc.Slide 40 Cycle of Life: Skin  Adults  Development and activation of sebaceous and sweat glands  Increased sweat production Body odor Body odor  Increased sebum production Acne Acne

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 41 Cycle of Life: Skin  Old age  Decreased sebaceous and sweat gland activity Wrinkling (Figure 6-21) Wrinkling (Figure 6-21) Decrease of body’s ability to cool itself Decrease of body’s ability to cool itself

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 42 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