CHAPTER 6: SKIN AND THE INTEGUMENTARY SYSTEM

OBJECTIVES:

1. Explain why the skin is called the cutaneous membrane.

2. Name the layers of the skin, describe the structure (tissues) of each, and name a general function of each.

3. Discuss the four cell types present in the epidermis.

4. List the four/five layers of the epidermis and explain the process of keratinization.

5. Explain the protective role of keratin, and in turn, the epidermis.

6. Name the pigment responsible for skin and hair color, and explain how people of different races (i.e. and skin color) differ in regards to it, and the cell that produces it.

7. List some factors that promote the production of melanin (besides DNA).

8. Distinguish between the papillary layer and reticular layer of the dermis, and locate the appropriate sensory receptor in each of these layers.

9. Compare and contrast Meissner's and Pacinian Corpuscles in terms of their structure, function, and location.

10. Describe the structure and function of the subcutaneous layer.

11. Explain what is meant by the term epidermal derivative, and list four examples.

12. Describe the general structure of a hair follicle and identify two other structures that are usually associated with them.

13. Distinguish between merocrine (eccrine) and apocrine sweat glands in terms of structure, secretion content and odor, activation, and major body locations.

14. Name two modified apocrine glands of the skin.

15. Describe the structure, function, secretion, and location of sebaceous glands.

16. Discuss the many functions of skin.

17. Describe some major homeostatic imbalances of the skin.

18. Sketch a typical layer of skin and label each layer and all structures. Then in complete sentences, discuss the function of each layer and structure.

I. INTRODUCTION

The integumentary system is the first body system studied. Before we begin any study of a body system, we will first think about the organs/tissues that work together to perform the function(s) of that system.

The integumentary system consists of a major organ, skin, and many epidermal derivatives (accessory organs), which include hair follicles, sebaceous glands, sweat glands, and nails.

In addition, the organs of the integumentary system are composed of many different tissues that perform common functions. Look at Figure 6.1, page 159 and Figure 6.2, page 160, and name as many different tissues as you can. These tissues include stratified squamous epithelium, glandular epithelium, dense irregular CT, smooth muscle tissue, adipose tissue, and nervous tissue. The functions that these tissues collectively perform are many. Functions of the skin include protection, excretion, regulation of body temperature, sensory reception, immunity, synthesis of Vitamin D, and blood reservoir.

II. SKIN AND ITS TISSUES (Cutaneous Membrane)

A. General Structure: See Fig 6.2, page 160. 1. Two distinct regions or layers compose the skin: a. Epidermis = outermost layer;

o keratinized stratified squamous ET.b. Dermis = inner layer;

o keratinized epithelium (hair follicles),o glandular epithelium (sweat, sebaceous glands), o dense irregular CT (collagen), o smooth muscle tissue (arrector pili muscles), o nervous tissue (Meissner's & Pacinian Corpuscles), ando blood vessels.

2. Subcutaneous layer = adipose tissue;distinct layer beneath skinalso called hypodermis

II. SKIN AND ITS TISSUES (Cutaneous Membrane)

B. Skin Functions

1. Protection:o Physical barrier

a. from water loss;b. from injury;c. from chemicals and microorganisms.

o Chemical barriera. pH or 5-6b. prevents microorganism growth

o Biological barriera. Langerhan’s cells (epidermis)b. Macrophages and mast cells (dermis)

2. Excretion (minimal, most through kidneys!):o urea;o uric acid.

3. Regulation of body temperature: Review negative-feedback mechanisms from Ch. 1 and see Figure 6.11, page 170.

4. Cutaneous Sensation:o Light touch detection = Meissner's Corpuscle's;

a. egg-shaped;b. located in dermal papillae;c. populate areas in the fingertips, palms, soles, eyelids, tip of

tongue, nipples, clitoris, tip of penis.

o Pressure detection = Pacinian Corpuscle's;a. onion-shaped;

b. located in deep dermis and subcutaneous regions;

5. Vitamin D Synthesis:

o UV rays in sunlight activate its synthesis;o Vitamin D is required for bone homeostasis.

6. Blood Reservoir:o The dermis houses about 10% of the body's blood vessels.o Skin only requires 1-2% of the body’s blood

7. Immunity:o Langerhan’s cells (macrophages);

o interact with T-helper cells in immune responses.

II. SKIN AND ITS TISSUES (Cutaneous Membrane)

C. Epidermis: 1. Structure = keratinized stratified squamous epithelium;

See Fig 6.3, page 161 and Table 6.1, page 161.

a. Four distinct layers determined by the extent of keratinization in the epithelial cells:

1. Stratum corneum = outermost layer.

o composed of dead epithelial cells filled with the

protein keratin;

*** Stratum lucidum = translucent layer cells separating s. corneum from s. granulosum.

o extra layer only in thick skin of soles & palms;

2. Stratum granulosum is composed of 3-5 layers of flattened granular cells (filled with keratin granules);

3. Stratum spinosum is composed of many layers of spiky cells with large nuclei;

4. Stratum basale (germinativum)= innermost layer;

o directly above basement membrane; o composed of a single row mitosing cuboidal

epithelial cells and o composed of melanocytes.

a. specialized cells that produce the pigment melanin.

b. See Figure 6.4, page 162, which illustrates the pigmentation in melanocytes.

2. Main Function = Protection (keratin): a. prevents moisture loss (waterproof); b. prevents injury by penetration; c. prevents microorganisms/chemicals entry

II. SKIN AND ITS TISSUES (Cutaneous Membrane)

C. Epidermis:

3. Pigment = Melanin: See Fig 6.4, page 162.

a. determines skin color: b. is produced by melanocytes in stratum

basale (germinativum);

D. Dermis: inner layer of skin; binds epidermis to underlying tissues.

1. Structure: See Fig 6.2, page 160.

a. two distinct layers: 1. papillary layer (20%) is below epidermis:

o composed of loose areolar CT;o surface forms dermal papillae (finger-like

projections into the epidermis) that form fingerprints in thick skin

o Meissner's Corpuscles (sensory receptor for light touch).

2. reticular layer (80%) = dense irregular CT;

o bundles of collagen fibers, o elastic fibers, and o reticular fibers which give skin itso strength and resiliency.o Pacinian corpuscles –sensory receptors for deep

pressure

b. The dermis houses epidermal derivatives or accessory organs (see below).

2. Main Function = nourishment of epidermis.

E. Subcutaneous Layer (hypodermis) = beneath skin.1. Structure = adipose tissue & blood vessels;2. Function = insulation.

III. ACCESSORY ORGANS OF THE SKIN (Epidermal Derivatives)

A. Hair Follicles: See Fig 6.5 and 6.6, page 165. 1. Structure: a. root or base in deep dermis; b. follicle throughout dermis; c. hair shaft in epidermis.

2. Keratinization a. cells are epithelium; b. cells in root = active mitosis; c. cells in follicle = maturing & accumulating

keratin; d. cells in epidermis = dead epithelial cells;

full of keratin = exposed hair or hair shaft.

3. Pigment = Melanin

4. Arrector Pili Muscle = a bundle of smooth muscle associated with every hair follicle. See Fig 6.5a, page 165.a. causes hair to stand on end ("goose bumps") when frightened or

cold.

B. Nails: See Fig 6.7, page 167.1. Epithelium undergoing keratinization (active mitosis in lunula).

2. Functions: a. manipulation;b. protection of digit ends.

C. Sebaceous Glands: See Fig 6.8, page 167.

1. holocrine gland (simple cuboidal epithelium);

2. associated with every hair follicle;

3. Secretion (holocrine) = sebum (i.e. oil).a. fat b. cellular material

4. Sebum is secreted into hair follicle;

5. Function: Sebum keeps skin & hair soft, pliable and virtually waterproof!

6. Disorders: a. acne (hypersecretion of sebum; ducts clog &

inflame); See Clinical Application 6.3, page 169.

b. seborrhea (hyperproduction of sebum; oily scales)

III. ACCESSORY ORGANS OF THE SKIN (Epidermal Derivatives)

D. Skin Glands (Sweat Glands or Sudoriferous Glands) 1. Two types

(based on glandular secretion): See Fig 6.9 & 6.10, page 168.

a. Merocrine (Eccrine) Glands:

Structure: 1. coil in deep dermis2. duct in dermis3. pore at surface

Characteristics: 1. respond to

elevated temperature / exercise 2. no odor in

secretion 3. function

throughout life 4. not associated

with hair follicles 5.

Location: forehead

neck

back Secretion (merocrine) = water plus

1. salts and 2. wastes (urea and uric acid)

b. Apocrine glands:

Structure:ducts terminate into hair follicles

Characteristics: 1. respond to

stress / emotions 2. odor in

secretion 3. begin to

function at puberty & continue through life 4. associated

with hair follicles

5.Location: armpits

groin

Secretion (apocrine) = sweat above plus 1. oil and 2. cellular debris.

Modified Apocrine Glands 1. Ceruminous

glands = external ear; secretion = earwax;2. Mammary glands = breasts; milk.

***Note that the above structures under III. ACCESSORY ORGANS OF THE SKIN (Epidermal Derivatives) are epithelial in nature and are actually specialized parts of the epidermis, even though their location is within the dermis.

IV. REGULATION OF BODY TEMPERATURE – normally near 98.6 F set point

A. Heat production and loss.

1. Heat production is mostly a by-product of cellular metabolism.

2. Heat loss is controlled by regulating dermal blood flow.a. Vasodilation – increases dermal blood flow, which also increases

heat lossb. Vasoconstriction – decreases derma blood flow which decreases

heat loss

3. Heat loss is by four methodsa. Radiation

o most heat loss by this modeo infrared heat rays move from area of high heat (i.e. the

blood) to areas of low heat (i.e. the environment)b. Conduction

o less heat losso heat moves by physical contacto the reason the seat you sit in is warm when you stand up

c. Convectiono heat loss to surrounding airo increases as air movement increases, that is why turning on

a fan cools your bodyd. Evaporation

o heat loss varieso if heat increases our sweating increases, so we lose more

heat by evaporating the sweat on the surface of our skin

4. Low body temperatures require heat loss to be minimizeda. The Hypothalamus signals for sweating to

decrease (decreasing heat loss by evaporation) and dermal vasoconstriction (decreasing heat loss by radiation)

b. Usually this brings the body temperature back to normal

5. If the body temperature remains low after the above action

a. Heat must be producedb. Shivering occurs and the tiny muscle contractions

involved produce heatc. See Figure 6.11 page 170

IV. REGULATION OF BODY TEMPERATURE

B. Problems in Temperature Regulation

1. Hyperthermia – elevated body temperaturea. Two common causes

o humid air decreases evaporationo air temperature exceeds body temperature, thus heat is

gained not losto See Clinical Application 6.4 page 171.

2. Hypothermia – low body temperaturea. very dangerous if core body temperature drops below 94 Fb. limbs can withstand about 65 F because they contain no vital

organsc. cause is intentional during some surgical procedures, see box on the bottom of page 171.

V. SKIN COLOR

A. Genetic Factors

1. People of different races have essentially the same # of melanocytes, but the amount of melanin produced varies (determined by DNA);

B. Environmental Factors affect melanin production: by affecting gene expression

1. UV rays, 2. chemicals, 3. drugs (antihistamines & antibiotics);

C. Physiologic Factors may affect skin color (but not melanin production):

1. Carotene may accumulate in s. corneum = orange; 2. Hemoglobin (Hb) in dermal blood vessels =

pink; 3. Lack of Hb in dermal blood vessels = blue

(cyanosis.)4. Inability to breakdown Hb (liver problems) = yellow (jaundice)

VI. HEALING OF WOUNDS AND BURNSInflammation – process that involves blood flow changes and chemical signaling leading to healing.

A. Cuts

1. Epidermal cuts are closed by increased cell division in the stratum basale

2. Deep cuts involve blood vessel damage resulting in:

a. Inflammationb. Blood clotting (See Hemostasis Chapter 14, pages 526-531)c. Scab formationd. Fibroblast infiltration and repaire. Scab falls offf. Scar may or may not remaing. See Figure 6.13 page 174

B. Burns

1. Superficial partial-thickness burns (1st degree)

a. Epidermis onlyb. Reddening due to increased blood flowc. Mild paind. Common in sunburn e. Heals in a few days-2 weeks

2. Deep partial-thickness burns (2nd degree)

a. Epidermis and some dermal damageb. Reddening and blistering caused by blood vessel damagec. Moderate paind. Common to physical contact with hot objectse. Heals in 2-6 weeks without scars unless infected

3. Full-thickness burns (3rd degree)

a. Epidermis, entire dermis, and potentially subcutaneal damageb. Dry, leathery tissue with red or black colorc. Severe paind. Caused by prolonged heat or chemical contact

e. Healing rarely occurs due to lack of surviving skin cells, skin replacements (grafts) are usually needed, usually extensive scarringo Autograft – transplant from undamaged area of yourselfo Homograft – temporary transplant from cadavero Skin substitutes – From Science to Technology 5.2 page 153

VI. HEALING OF WOUNDS AND BURNS

B. Burns

4. Body Surface affected

a. Estimated by “rule of nines”b. Important for determining treatment and prognosisc. See Figure 6.14 page 175.

VII. LIFE SPAN CHANGES

A. Aging skin exhibits:1. wrinkling2. sagging3. age spots or liver spots

a. See Fig 6.15, page 176.

B. Efficient regulation of body temperature declines with age.1. The number of sweat glands changes.2. Capillary beds in the skin shrink.

C. Synthesis of vitamin D declines as skin ages, which affects skeletal health.

VIII. HOMEOSTATIC IMBALANCES OF THE SKINThroughout the text of each chapter, your authors present selected imbalances, disorders, and diseases of each system. Although you may only discuss some major disorder in class, these disorders and diseases are very interesting to learn about. You are strongly encouraged to study them.

A. Epidermolysis bullosa. See blue box on page 158.B. Psoriasis. See blue box on page 160.C. Contact dermatitis. See blue box on page 164.D. Rashes. See Table 6.2, page 161.E. Skin Cancer = carcinoma. See Clinical Application 6.1, pages 163.F. Folliculitis. See blue box on page 166.G. Hair loss. See Clinical Application, page 166.H. Acne. See Clinical Application, page 169.I. Hypothermia. See blue box on page 171.J. Albinism. See Fig 4.26, page 127, Fig 6.12, page 172, and blue box on page 172.K. Elevated body temperature. See Clinical Application 6.4, page 171.

L. Jaundice. See blue box on page 172.

IX. COMMON SKIN DISORDERS – See pages 176 and 178.

X. Innerconnections between the Integumentary System and other organ systems: Page 177.

Chapter 6: Skin and the Integumentary System

I. 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, epithelial

tissue, 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.

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 travel, 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 palms of the hand 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.

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.

3. The dermis binds the epidermis to the subcutaneous layer.

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. Subcutaneous Layer

1. The subcutaneous layer consists of loose connective tissue and adipose tissue.

2. No sharp boundary separates the dermis and subcutaneous layer because the

fibers of the dermis are continuous with the fibers of the subcutaneous layer.

3. The adipose tissue of the subcutaneous layer insulates the body.

4. The subcutaneous layer contains major blood vessels that supply the skin.

II. Accessory Organs 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 cell 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 keratinocytes.

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 albinos lack melanin.

12. Red hair contains an iron pigment called trichosiderin.

13. Hairs appear gray from a mix of pigmentation and unpigmentation.

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.

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 and

pliable.

5. Sebaceous glands are not found on palms and soles.

6. Sebaceous glands open directly onto 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.

10. Eccrine glands respond to heat.

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 axilla, groin, and around the

nipples.

17. Ceruminous glands of the external ear canal and secrete cerumen.

18. Mammary glands secrete milk.

III. 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 heat from warm areas to cooler areas.

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 to contract

slightly 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 an illness.

5. Hypothermia can lead to mental confusion, lethargy, and loss of

consciousness.

6. Children and the elderly are at a higher risk for developing hypothermia.

IV. Skin Color

A. 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.

B. Environmental Factors

1. Environmental factors such as sunlight and X rays affect skin color.

2. These factors stimulate melanocytes to produce more pigment.

3. Tans fade as pigmented epidermal cells become keratinized and wear away.

C. 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, less blood enters skin and skin appears

pale.

5. Carotene is a yellow-orange pigment found in certain vegetables.

6. Carotene can give skin a yellowish color.

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,

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 fibers that

bind the edges of the wound together.

6. Connective tissue matrix secretes 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 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 organs of the skin

that survive the burn.

5. A third degree burn is one that affects the entire thickness of skin.

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 silicon,

polyurethane or nylon.

11. The treatment of a burn patient requires estimating the extent fo 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 nails 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

follicle shrink, and the number of dermal blood vessels decrease.

J. Vitamin D is necessary for calcium absorption.