Shier, Butler, and Lewis: Hole’s Human Anatomy and Physiology, 12th ed. Chapter 6: Skin and the Integumentary System

Chapter 6: Integumentary System

I. Introduction and
II. Skin and Its Tissues
A. Introduction
1. The skin is composed of several kinds of tissues.
2. Skin is a protective covering that prevents many harmful substances from entering the body.
3. Skin also retards water loss and helps regulate body temperature.
4. Skin houses sensory receptors and contains immune system cells.
5. Skin synthesizes vitamin D and excretes a small amount of waste products.
6. The two distinct layers of skin are epidermis and dermis.
7. The outer layer is called the epidermis and is composed of stratified squamous epithelium.
8. The inner layer is called dermis and is made up of connective tissues, muscle tissue, nervous tissue, and blood.
9. A basement membrane separates the two skin layers.
10. The subcutaneous layer is beneath the dermis.
11. The subcutaneous layer is composed of loose connective tissues and adipose tissues.
12. No sharp boundary separates the dermis and subcutaneous layer because the fibers of the dermis are continuous with the fibers of the subcutaneous layer.
13. The adipose tissue of the subcutaneous layer insulates the body.
14. The subcutaneous layer also contains major blood vessels that supply the skin.
B. Epidermis
1. The epidermis lacks blood vessels.
2. The deepest layer of the epidermis is called the stratum basale.
3. The stratum basale is nourished by blood vessels in the dermis.
4. Cells of the stratum basale can divide and grow because they are nourished so well.
5. When new cells enlarge they push old epidermal cells away from the dermis toward the surface of skin.
6. The farther the cells are moved, the poorer their nutrient supply becomes and eventually they die.
7. Older skin cells are called keratinocytes and are held together with desmosomes.
8. Keratinization is the accumulation of keratin in epidermal cells which hardens the epidermis.
9. As a result of keratinization many layers of tough, tightly packed cells
accumulate in the epidermis.
10. The outermost layer of the epidermis is called the stratum corneum.
11. The epidermis is thickest on the palms of the hands and the soles of the feet.
12. Most areas of epidermis have 4 layers.
13. The four layers starting with the deepest are stratum basale, stratum spinosum, stratum germinativum, and stratum corneum.
14. An additional layer called stratum lucidum is in thickened skin of the palms and soles.
15. In healthy skin, production of epidermal cells is balanced with loss of dead cells from the stratum corneum.
16. The rate of cell division increases where the skin is frequently rubbed or pressed.
17. Calluses are a thickening of the stratum corneum.
18. Corns are keratinized conical masses on the toes.
19. Specialized cells in the epidermis called melanocytes produce melanin.
20. Melanin provides skin color and absorbs UV radiation.
21. Melanocytes lie in the stratum basale and in the underlying connective tissues of the dermis.
22. The extensions of melanocytes transfer melanin granules to epidermal cells by a process called cytocrine secretion.
C. Dermis
1. The boundary between the dermis and epidermis is uneven because the epidermis projects inward and the dermis has papillae between the ridges of the epidermis.
2. Fingerprints form from the undulations of the dermis and epidermis at the distal end of the palmar surface of a finger.
3. The dermis binds the epidermis to the underlying tissues.
4. The dermis is largely composed of irregular dense connective tissue that includes tough collagenous fibers and elastic fibers in a gel-like ground substance.
5. The dermis also contains smooth muscles that can wrinkle the skin of the scrotum.
6. Some smooth muscle of the skin is associated with hair follicles.
7. In the face, skeletal muscles are anchored to the dermis.
8. Nerve cell processes are scattered throughout the dermis.
9. Pacinian corpuscles are stimulated by heavy pressure.
10. Meissner’s corpuscles are stimulated by light touch.
D. Genetic Factors
1. Regardless of racial origin, all people have about the same number of melanocytes in their skin.
2. Differences in skin color result from the differences in the amount of melanin melanocytes produce.
3. The more melanin produced, the darker the skin.
4. The distribution and size of pigment granules within melanocytes also influence skin color.
E. Environmental Factors
1. Environmental factors such as sunlight, ultraviolet light from sunlamps, and X-rays affect skin color.
2. These factors stimulate melanocytes to produce more pigment and transfer it to nearby epidermal cells within a few days.
3. Tans fade as pigmented epidermal cells become keratinized and wear away.
F. Physiological Factors
1. When blood is well oxygenated, the blood pigment hemoglobin is bright red and the skin of light-complexioned people appears pink.
2. When blood oxygen concentration is low, hemoglobin is dark red and the skin appears bluish.
3. If dermal blood vessels are dilated, more blood enters skin and skin appears pinkish or reddish.
4. If dermal blood vessels are constricted, more blood enters the dermis,
and causes reddening the skin of a light-complexioned person.
5. Carotene is a yellow-orange pigment found in certain vegetables.
6. Carotene can give skin a yellowish color.
III. Accessory Structures of the Skin
A. Hair Follicles
1. Hair is present on all skin surfaces except the palms, soles, lips, nipples, and parts of external reproductive organs.
2. A hair follicle is a group of epidermal cells at the base of a tubelike depression in the dermis of skin.
3. A follicle extends from the surface of skin into the dermis.
4. The hair root is the portion of hair embedded in skin.
5. The hair papilla is a projection of connective tissue at the end of the hair follicle. It contains blood vessels.
6. The hair shaft is the portion of hair that extends from the surface of skin.
7. A hair is composed of dead epidermal cells.
8. Baldness results when hairs fall out and are not replaced.
9. Genes determine hair color by directing the type and amount of pigment that epidermal melanocytes produce.
10. Dark hair has more melanin than blond hair.
11. White hair of people with albinism lacks melanin.
12. Red hair contains an iron pigment called trichosiderin.
13. Hairs appear gray from a mix of pigmented and unpigmented cells.
14. An arrector pili muscle is a band of smooth muscle and attaches to hair follicles.
15. Goose bumps are produced when arrector pili muscles contract.
B. Nails
1. Nails are protective coverings on the ends of fingers and toes.
2. Each nail consists of a nail plate that overlies a surface of skin called the nail bed.
3. The lunula of a nail is the whitish, thickened, half-moon shaped region at the base of a nail plate with the most active growth.
C. Skin Glands
1. Sebaceous glands contain groups of specialized epithelial cells and are associated with hair follicles.
2. Sebaceous glands are holocrine glands and their cells produce sebum.
3. Sebum is a mixture of fatty material and cellular debris.
4. Sebum is secreted into hair follicles and helps keep hair and skin soft, pliable and waterproof.
5. Sebaceous glands are not found on palms and soles.
6. Sebaceous glands open directly onto the surface of the skin in some regions, such as the lips, corners of the mouth, and parts of the external reproductive organs.
7. Sweat glands are also called sudoriferous glands.
8. Each sweat gland consists of a tiny tube in the dermis or superficial subcutaneous layer.
9. The most numerous sweat glands are eccrine glands.
10. Eccrine glands respond to body temperature elevated by environmental heat or exercise.
11. Eccrine glands are common on the forehead, neck, and back.
12. A pore is the opening of a sweat gland duct.
13. Sweat contains water, wastes, and salts.
14. Apocrine glands become active at puberty.
15. They can wet certain areas of skin when a person is nervous or stressed.
16. Apocrine glands are most numerous in the axillary regions, groin, and around the nipples.
17. Ceruminous glands of the external ear canal secrete ear wax.
18. Mammary glands secrete milk.
IV. Regulation of Body Temperature
A. Introduction
1. Regulation of body temperature is important because even slight shifts can disrupt the rates of metabolic reactions.
2. A normal temperature of deeper body parts remains close to 37oC.
B. Heat Production and Loss
1. Heat is a product of cellular metabolism.
2. When body temperature rises above the set point, nerve impulses stimulate structures in the skin and other organs to release heat.
3. During physical activity, active muscles release heat, which the blood carries away.
4. When warmed blood reaches the hypothalamus, muscles in the walls of dermal blood vessels relax.
5. As dermal blood vessels dilate, heat escapes to the outside world.
6. Skin reddens because dermal blood vessels are dilated.
7. The primary means of body heat loss is radiation.
8. Radiation is the spread of infrared heat from warm surfaces to cooler surroundings.
9. Conduction is the movement of heat into molecules of cooler objects.
10. Convection is the continuous circulation of air over a warm surface.
11. Evaporation is the change of a liquid to a gas.
12. When sweat evaporates, it carries heat away from the skin surface.
13. When body temperature falls below the set point, muscles of dermal blood vessels constrict which decreases the flow of blood through the skin.
14. When body temperature falls, sweat glands become inactive.
15. When body temperature continues to fall, small groups of muscles contract rhythmically to produce shivering.
C. Problems in Temperature Regulation
1. Hyperthermia is a rise in body temperature.
2. If air temperature is high, heat loss by radiation is less effective.
3. Hypothermia is a low body temperature.
4. Hypothermia can result from prolonged exposure to cold or as part of an illness.
5. Hypothermia can lead to mental confusion, lethargy, and loss of consciousness.
6. Elderly, very thin individuals, homeless and the very young are at a higher risk for developing hypothermia.
V. Healing of Wounds and Burns
A. Introduction
1. Inflammation is a normal response to injury or stress.
2. During inflammation, blood vessels dilate and become more permeable.
3. Inflamed skin may become reddened, swollen, warm, and painful to the touch.
4. The dilated blood vessels provide the tissues with more nutrients and oxygen, which aids healing.
5. The specific events of healing depend on the nature and extent of the injury.
B. Cuts
1. If a break in the skin is shallow, epithelial cells are stimulated to divide more rapidly than normal.
2. If a cut extends into the dermis or subcutaneous layer, blood vessels break and the escaping blood forms a clot.
3. A clot consists mainly of fibrin, plasma, blood cells, and platelets.
4. A scab is a blood clot and dried fluids.
5. Fibroblasts migrate into the injured area and begin forming new collagenous fibers that bind the edges of the wound together.
6. Connective tissue matrix releases growth factors that stimulate certain cells to divide and regenerate damaged tissues.
7. As healing continues, blood vessels extend into the area beneath the scab.
8. Phagocytic cells remove dead cells and other debris.
9. A scar results when the wound is extensive.
10. A granulation consists of a branch of a blood vessel, and a cluster of collagen-secreting fibroblasts.
C. Burns
1. A first degree burn is one that only affects the epidermis.
2. A second degree burn is one that affects a part of the dermis and epidermis.
3. Blisters appear in second degree burns.
4. The healing of second degree burns depends on accessory structures of the skin that survive the burn.
5. A third degree burn is one that destroys the epidermis, dermis, and the accessory structures.
6. In a third degree burn, the skin becomes dry and leathery.
7. If a third degree burn is extensive, treatment may involve removing a thin layer of skin from an unburned region of the body and transplanting it to the injured area.
8. An autograft is a graft from the same person.
9. A homograft is a graft from a cadaver.
10. Skin substitutes include amniotic membranes, membranes of silicone, polyurethane or nylon.
11. The treatment of a burn patient requires estimating the extent of the body’s surface that is affected.
12. To estimate, physicians use the rule of nines.
13. This rule divides the skin’s surface into 11 areas of 9% each.
VI. Life-Span Changes
A. Aging skin affects appearance, temperature regulation and vitamin D production.
B. Age spots or liver spots are patches of pigments.
C. The dermis becomes reduced as synthesis of the connective tissue proteins collagen and elastin slows.
D. Wrinkling and sagging skin result from the shrinking of the dermis and loss of fat from the subcutaneous layer.
E. Skin becomes drier because sebaceous glands produce less oil.
F. Slowed melanin production causes gray or white hair.
G. Nail growth is impaired because the blood supply to the nail beds is diminished.
H. Sensitivity to pain and pressure diminishes with age.
I. An older person is less able to tolerate heat because the sweat glands and hair follicles shrink, and the number of dermal blood vessels decreases.
J. Vitamin D is necessary for bone tissue to absorb calcium.