1. Chapter 6: Skin and Its Appendages
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Chapter 6: Skin and Its Appendages
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2. INTRODUCTION Skin (integument) is the body’s largest organ
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INTRODUCTION
Skin (integument) is the body’s largest organ
Approximately 1.6 to 1.9 m2 in average-sized adult
Integumentary system describes the skin and its appendages: hair, nails, and skin glands
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3. STRUCTURE OF THE SKIN Skin classified as a cutaneous membrane
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STRUCTURE OF THE SKIN
Skin classified as a cutaneous membrane
Two primary layers: epidermis and dermis; joined by dermoepidermal junction (Figures 6-1 and 6-2)
Hypodermis lies beneath dermis
Thin and thick skin (Figure 6-3)
Thin skin covers most of the body’s surface (1 to 3 mm thick)
Thick skin covers soles and palms (4 to 5 mm thick)
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7. STRUCTURE OF THE SKIN: EPIDERMIS
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STRUCTURE OF THE SKIN: EPIDERMIS
Epidermis
Cell types (Figure 6-4)
Keratinocytes: constitute more than 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 and filter ultraviolet (UV) light
Epidermal dendritic cells: branched antigen-presenting cells; 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
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9. STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
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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 spinosum (spiny layer): cells arranged in eight to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNA
Stratum germinativum (growth layer): another name for stratum basale or stratum spinosum and stratum basale together
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10. STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
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STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
Stratum granulosum (granular layer): cells arranged in two to four layers and filled with keratohyalin granules; contains 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; thin squamous cells, dead cells filled with keratin (barrier area – to environment and water loss)
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11. STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
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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—approximately 35 days
Epidermal growth factor regulates epidermal growth and repair
Shortened turnover time due to abrasion 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
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12. STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
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STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
Dermoepidermal junction
A basement membrane with unique fibrous elements and a polysaccharide gel “glue” the epidermis to the dermis below
The junction is a partial barrier to the passage of some cells and large molecules
Separation of the epidermis from the DEJ result in blisters
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13. STRUCTURE OF THE SKIN: DERMIS
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STRUCTURE OF THE SKIN: DERMIS
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
Contains various structures
Arrector pili muscles and hair follicles (Figure 6-5)
Sensory receptors (Figure 6-6)
Sweat and sebaceous glands
Blood vessels
Rich vascular supply plays a critical role in temperature regulation
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16. STRUCTURE OF THE SKIN: DERMIS (cont.)
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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 and 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
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17. STRUCTURE OF THE SKIN: DERMIS (cont.)
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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: patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines (Figure 6-7)
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19. STRUCTURE OF THE SKIN: HYPODERMIS
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STRUCTURE OF THE SKIN: HYPODERMIS
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
Rich blood supply makes it a perfect site for fast a relatively pain free absorption of injected material – insulin
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SKIN COLOR
Melanin
Basic determinant is quantity, type, and distribution of melanin
Types of melanin
Eumelanin: group of dark brown, almost black, melanins
Pheomelanin: group of reddish and orange melanins
Melanin formed from tyrosine by melanocytes (Figure 6-8)
Melanocytes release melanin in packets called melanosomes
Melanosomes are ingested by surrounding keratinocytes and form a cap over the nucleus
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22. SKIN COLOR (cont.) Albinism: congenital absence of melanin
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SKIN COLOR (cont.)
Albinism: congenital absence of melanin
Expression of melanin genes regulated by tyrosinase, exposure to sunlight (UV radiation), and certain hormones, including melanocortins (adrenocorticotropic hormone, alpha melanocyte stimulating hormone) and endothelin-1 (Figures 6-9 and 6-10)
Cumulative effects of UV ray exposure may produce age spots (Figure 6-11)
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25. SKIN COLOR: OTHER PIGMENTS
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SKIN COLOR: OTHER PIGMENTS
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
Cyanosis: bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide (Figure 6-12)
Bruising can cause a rainbow of different colors to appear in the skin (Figure 6-13)
Other pigments: from cosmetics, tattoos, and bile pigments in jaundice (Box 6-4)
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28. FUNCTIONS OF THE SKIN Protection (Table 6-2)
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FUNCTIONS OF THE SKIN
Protection (Table 6-2)
Physical barrier to microorganisms
Barrier to chemical hazards
Reduces potential for mechanical trauma
Prevents dehydration
Protects from excess UV ray exposure (melanin function)
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29. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (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
Functions
Antibacterial, antifungal activity
Lubrication
Hydration of skin surface
Buffer of caustic irritants
Blockade of toxic agents
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30. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (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 and uric acid
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31. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (cont.)
Sensation
Skin acts as a sophisticated sense organ
Somatic sensory receptors detect stimuli that detection of pressure, touch, temperature, pain, and other general senses
Flexibility
Skin is supple and elastic, thus permitting change in body contours without injury
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32. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (cont.)
Excretion
Water
Urea/ammonia/uric acid
Hormone (vitamin D) production (Figure 6-14)
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
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34. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (cont.)
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
Heat production
By metabolism of foods in skeletal muscles and liver
Chief determinant of heat production is the amount of muscular work being performed
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35. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (cont.)
Homeostasis of body temperature
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 6-15)
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 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
Conduction: transfer of heat to any substance 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
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37. FUNCTIONS OF THE SKIN (cont.)
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FUNCTIONS OF THE SKIN (cont.)
Homeostatic regulation of heat loss (Figure 6-16)
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
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39. APPENDAGES OF THE SKIN Hair (Figure 6-17) Development of hair
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APPENDAGES OF THE SKIN
Hair (Figure 6-17)
Development of hair
Distribution is 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
Coarse pubic and axillary hair that develops at puberty called terminal hair
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
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41. APPENDAGES OF THE SKIN: HAIR (cont.)
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APPENDAGES OF THE SKIN: HAIR (cont.)
Appearance of hair
Color: result of different amounts, distribution, types of melanin in cortex of hair (Figure 6-18)
Growth: 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 6-19)
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43. APPENDAGES OF THE SKIN (cont.)
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APPENDAGES OF THE SKIN (cont.)
Nails (Figure 6-20)
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
Nail bed: layer of epithelium under nail body; contains abundant blood vessels
Appears pink under translucent nails
Nails may have pigmented streaks (Figure 6-21)
Separation of a nail from the nail bed is called onycholysis (Figure 6-22)
Growth: nails grow by mitosis of cells in stratum basale beneath the lunula; average growth about 0.5 mm/week, or slightly over 1 inch per year
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47. APPENDAGES OF THE SKIN (cont.)
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APPENDAGES OF THE SKIN (cont.)
Skin glands (Figure 6-23)
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
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
Odor is from bacteria feeding off gland production
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49. APPENDAGES OF THE SKIN: SKIN GLANDS (cont.)
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APPENDAGES OF THE SKIN: SKIN GLANDS (cont.)
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
From hair follicles
Found in dermis except in palms and soles
Secretion increases in adolescence; may lead to formation of pimples and blackheads
Ceruminous glands
Modified apocrine sweat 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 can cause blockage of ear canal and loss of hearing
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50. CYCLE OF LIFE: SKIN Children Adults Old age
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CYCLE OF LIFE: SKIN
Children
Skin is smooth, unwrinkled, and characterized by elasticity and flexibility
Few sweat glands
Rapid healing
Adults
Development and activation of sebaceous and sweat glands
Increased sweat production
Body odor
Increased sebum production
Acne
Old age
Decreased sebaceous and sweat gland activity
Wrinkling (Figure 6-24)
Decrease in body’s ability to cool itself
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52. THE BIG PICTURE: SKIN AND THE WHOLE BODY
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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
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53. Severity of Burns First-degree burns
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Severity of Burns
First-degree burns
Only epidermis is damaged
Skin is red and swollen
Second-degree burns AKA partial thickness burns
Epidermis and upper dermis are damaged
Skin is red with blisters
Third-degree burns
Destroys entire skin layer
Burn is gray-white or black
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