Chapter 7: Skin and Appendages

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Lesson 7-1 Objectives

• List six functions of the skin.• Define stratum germinativum and stratum

corneum.• Describe the two layers of the skinepidermis

and dermis.• List the two major functions of the

subcutaneous layer.

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Introduction

Skin (integument) is body’s largest organ

Integumentary system describes the skin and its appendages—the hair, nails, and skin glands

You shed about 1.5 lbs per year

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Skin Perspective • On average, 1 cm2 of

skin contains:– 3,000,000 cells– 10 hairs– 15 sebaceous glands– 3 feet of blood vessels– 700 sweat glands

– 3000 sensory cells at nerve endings

– 12 feet of nerves• 200 pain receptors• 2 cold receptors• 12 sensors for heat

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Functions of the Skin

• Serves as mechanical barrier• Protects internal structures • Participates in the immune response• Acts as a gland for vitamin D synthesis• Performs excretory function• Performs sensory role• Helps regulate body temperature

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Structure of the Skin

• Layers– Epidermis

• (lays upon dermis)

– Dermis (skin)• Subcutaneous

• a.k.a: Hypodermis

• Accessory structures

• Hair, nails, glands..etc.

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Overview Structure of the Skin

Skin classified as cutaneous membraneTwo primary layers—epidermis and dermis; joined by dermoepidermal junctionHypodermis lies beneath dermisThin 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

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Layers of EpidermisFrom deep to Superfical:• Stratum Basale

• A.k.a Stratum Germinativum

• Stratum Spinosum• Stratum Granulosum• Stratum Lucidum• Stratum Corneum• 2. **• 3. 4.

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Layers uncovered

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Epidermis: Outer Layer continued…• Layers of the epidermis

– Stratum corneum (surface layer); composed of dead, flattened cells that slough off , our horns

– Stratum germinativum (deepest), a.k.a. stratum basale: cells continuously dividing and moving toward surface

• Keratinization: The protein keratin makes skin cells hard, flat, and water resistant.

• (Keratinocytes…cells that actually produce protein) 14

Epidermal growth and repair

• Shortened turnover time increase thickness of the stratum corneum; results in callus formation

• Normally 10% to 12% of all cells in stratum basale enter mitosis daily

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Structure of the SkinDermopidermal junction (DEJ)A basement membrane Polysaccharide gel serve to “glue” the epidermis to the dermis belowPartial barrier to the passage of some cells and large molecules

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Dermis

• Our “hide”, strong and stretchy– “true skin”

• Lies under and supports the epidermis– Gives strength

• Sits on the subcutaneous layer or hypodermis• Embedded with accessory structures

– Includes blood vessels that nourish epidermis– Reservoir storage for water and electrolytes

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Dermis continued…• 2 major regions:

– Papillary: upper/superficial dermal layer • Pain receptors (free nerve endings)• Touch receptors: Meissner’s corpuscles• Allow for grip• Genetically unique= fingerprints• Arrector pili (goose bumps)

– Reticular: Deepest of skin layer• Blood vessel, sweat glands, oil glands• Pacinian corpuscles: Deep pressure receptors• Last line of defense• Leather 18

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Dermis (cont)During wound healingfibroblasts begin forming an unusually dense mass of new connective fibersif not replaced by normal tissue, this mass remains a scarCleavage lines (Figure 7-7)—patterns formed by the collagenous fibers of the reticular layer of the dermis

also called Langer’s lines20

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Langer’s lines

Scar formation

• Cleavage lines - patterns formed by the collagenous fibers of the reticular layer also

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Subcutaneous Layer: Hypodermis• A.k.a = subcutaneous layer• Connection point to tissue that lies beneath

skin• Highly vascularized• Two main roles:

– Its fat insulates body from extreme temperature changes.

– Its connective tissue anchors the skin to underlying structures.

• NOT PART OF THE SKIN23

Problems…

• Decubitus ulcers; Bed sores– Blood supply is cut off– Bedridden patients who

are not regularly moved– Pressure of bone on skin

eventually cuts off supply line

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Real life…

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Skin ColorDetermined by: genes, physiology, and sometimes pathologyDark pigment: Melanin• Eumelanin-dark brown-black• Pheomelanin-red-brown• Melanocyte= Make melanin

in epidermis(St.Basale)• Melanocyte malfunctions:

– Albinism (defect in melanin)– Vitiligo (loss of brown pigment)

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Skin color continued

• Beta-carotene: Orange-yellow (some veggies)– Presence of melanin overshadows carotene’s tint

in most people• Lipofuscin: brown-yellow age spots• Hemoglobin

– Red coloring from blood cells in dermis capillaries– Oxygen content determines the extent of red

coloring

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Skin Color (cont’d.)

• Physiological changes:– Blushing: Blood vessel dilation – Pallor: Blood vessel constriction

• Pathological changes:– Cyanosis or bluish tint: Poor oxygenation – Jaundice or yellowing: Bilirubin deposition (Bile

and Liver products)– Bronzing: Melanin overproduction– Ecchymosis: Black and blue bruising

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Accessory Structures: Hair• Functions: Detect

insects, protect eyes, keep dust out of lungs

• Hormones affect growth.

• Melanin influences color.

• Hair arises in epidermis.• Cosmetic role

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Developmental of Hair• Distribution-over entire body

– Except palms and soles of feet• Lanugo: fine and soft hair before birth• Vellus Hair: fine, barely noticeable hair,

childhood• Body Hair

– Head hair– Androgenic Hair: Coarse body hair– Terminal Hair: coarse pubic hair and axillary hair

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Make up of hair• Papilla—cluster of capillaries under germinal

matrix; “feed” follicle• Root(hair follicle): part of hair embedded in

follicle in dermis but hair develops from epidermis

• Shaft—visible part of hair• Medulla—inner core of hair• Cortex—outer portion

– What conditioner works on• Growth is erratic

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Accessory Structures: Nails

• Protect tips of fingers and toes from injury• Condition affected by oxygenation of blood

supply, trauma, and nutritional deficiencies

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Nails

• Consist of epidermal cells converted to hard keratin

• Nail body—visible part of each nail– It is what you trim

• Root—part of nail in groove hidden by fold of skin, the cuticle

• Lunula—moon-shaped white area nearest root

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Nails continued…

• Nail bed—layer of epithelium under nail body; contains abundant blood vessels– Appears pink under translucent nails

• Nails may have pigmented streaks• Growth—nails grow by mitosis of cells in

statum basale beneath the lunula– Average growth about 0.5 mm per week, or

slightly over 1 inch per year

Accessory Structures: Glands • Sebaceous glands:

– Oil glands– Secrete sebum and in

fetus vernix caseosa • Sudoriferous

– Sweat glands

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Sudoriferous Glands

• Apocrine glands: Found with hair follicles; more active at puberty– Axillary and Genital Regions

• Eccrine glands: Everywhere; Critical for temperature regulation

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Eccrine glands

• Most numerous sweat glands; quite small

• Over total body surface • Simple, coiled, tubular

glands• Function throughout life• Secrete perspiration, or

sweat; • Eliminate wastes and help

maintain a constant core temperature

• Hyperhidrosis: over sweating

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Apocrine gland

• Large; in subcutaneous layer• Limited distribution—axilla,

areola of breast, and around anus

• Simple, branched, tubular glands

• Begin to function at puberty• Thicker liquid full of nutrients

for bacteria– causing B.O.

Sweat and Its FunctionComposition

· Mostly water· Some metabolic waste· Fatty acids and proteins (apocrine only)

Function· Helps dissipate excess heat· Excretes waste products· Acidic nature inhibits bacteria growth

Odor is from associated bacteria

Sweet SweatTypes of modified sweat glands:• Mammary glands: Secrete milk• Ceruminous glands: Secrete ear wax

(cerumen)• Pheromones: Sex attractants

– Copuline (copulation)

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Black head vs. Pimple

• Sebaceous gland closure

• Blackhead– Partially clogged trapped

sebum– Black due to oxygen

exposure

• Pimple– Fully clogged pore– Infected and inflamed

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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)

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Surface film

• Barrier formed by mixing sweat and sebaceous glands with sloughed epithelial cells from skin surface

• Functions– Antibacterial, antifungal activity– Lubrication– Hydration of skin surface– Buffer of caustic irritants– Blockade of toxic agents

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 (small amounts)

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Functions continued…

• Hormone– (vitamin D) production Exposure of skin

synthesizes vitamin D– Blood transports = classified as a hormone

• Immunity– Phagocytic cells destroy bacteria

Body Temperature: Key Terms

• Core temperature: The inner parts of the body• Shell temperature: The surface areas of the

body• Thermoregulation: Balance of heat production

and heat loss

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Homeostasis of body temperature

Heat production By metabolism of foods in skeletal muscles

and liver Chief determinant of heat production is the

amount of muscular work being performedHeat loss

approximately 80% through the skinremaining 20% through the respiratory, digestive, and urinary tracts

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Temperature Regulation

• Hypothalamus– Heat lost by:

• Dilation of blood vessels

• Sweating

– Heat conserved by• Shivering• Blood vessel

constriction• Less sweat

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Issues in Temperature Regulation

• Hyperthermia: Syncope (fainting), cramps, heat exhaustion, heat stroke

• Hypothermia: Slowed metabolism, fibrillation (random heart beat)

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BurnsTissue damage and cell death caused by heat, electricity, UV radiation, or chemicals

· Associated dangers

· Dehydration

· Electrolyte imbalance

· Circulatory shock

Burns: Classified by Depth

• Partial thickness burns– First-degree– Second-degree

• Full-thickness burn– Third-degree

• Extends to muscle and bones– Fourth degree

Severity of Burns· First-degree burns

· Only epidermis is damaged

· Skin is red and swollen· Second degree 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

Types of Burns

1st Degree Burn 2nd Degree Burn

2nd vs. 3rd

Severe 2nd Degree Burn 3rd Degree Burn

3RD Degree Burns

Rules of Nines

· Way to determine the extent of burns

· Body is divided into 11 areas for quick estimation

· Each area represents about 9%

Rule of Nines

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· Burns are considered critical if:· Over 25% of body has second degree

burns

· Over 10% of the body has third degree burns

· There are third degree burns of the face, hands, or feet

Critical Burns

Burns: Classified by Extent

• “Rule of nines”

• Eschar (scab)– Acts like a

tourniquet– Breeds

bacteria– Secretes

toxins

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Roman breastplate; escharotomy

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Cycle of Life: Skin

Children Skin is smooth, unwrinkled, and

characterized by elasticity and flexibility

Few sweat glands Rapid healing

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Cycle of Life: Skin

Adults Development and activation of

sebaceous and sweat glands Increased sweat production; can

result in body odor Increased sebum production; can

result in acne

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Cycle of Life: Skin

Old age Decreased sebaceous and

sweat gland activity Wrinkling (Figure 7-24) Decrease in body's ability to

cool itself

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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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Skin Care

• All ages:– Reduce exposure to UV radiation.

• Especially in older adults:– Skin dries out more easily; retain moisture by

limiting excessive bathing and use of soap.– Thinner skin bruises more easily and does not

insulate as well.

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Skin, Drugs, and Chemicals

• Skin can absorb many chemicals.• Drug delivery systems:

• Hypodermic injections• Transdermal patches• Intradermal injections (allergy testing)• Topical applications

• Danger of absorption of toxins

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