chapter 7 skin and its appendages n.
Skip this Video
Loading SlideShow in 5 Seconds..
Chapter 7: Skin and Its Appendages PowerPoint Presentation
Download Presentation
Chapter 7: Skin and Its Appendages

Chapter 7: Skin and Its Appendages

224 Vues Download Presentation
Télécharger la présentation

Chapter 7: Skin and Its Appendages

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Chapter 7: Skin and Its Appendages Anatomy & Physiology

  2. Introduction • Skin (integument) is body’s largest organ • Skin measures approximately 1.6 to 1.8 m2 in average-sized adult • Integumentary system describes the skin and its appendages—the hair, nails, and skin glands 2

  3. Structure of the Skin • 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 3

  4. 4

  5. 5

  6. 6

  7. 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 7

  8. 8

  9. 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; stratumgerminativum (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 9

  10. 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) 10

  11. 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), insulin-like growth factor 1 (EGF-1), and growth hormone (GH) 11

  12. Structure of the Skin • Epidermal growth and repair (cont) • 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 • 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 12

  13. 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 13

  14. 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 14

  15. 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 15

  16. 16

  17. 17

  18. 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 18

  19. 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 19

  20. 20

  21. 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 21

  22. 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 22

  23. 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 23

  24. 24

  25. 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) 25

  26. 26

  27. 27

  28. 28

  29. 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 29

  30. 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) 30

  31. 31

  32. 32

  33. 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) 33

  34. 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 34

  35. 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 35

  36. 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 senses • Flexibility • Skin is supple and elastic, thus permitting change in body contours without injury • Excretion • Water • Urea/ammonia/uric acid 36

  37. 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 37

  38. 38

  39. 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 39

  40. 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 40

  41. 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 41

  42. 42

  43. 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 43

  44. 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 44

  45. 45

  46. 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 46

  47. 47

  48. 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 48

  49. 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) 49

  50. 50