1 essentials of human anatomy essentials of human anatomy skin

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Essentials of Human AnatomyEssentials of Human Anatomy

Skin

• Skin (integument) is body’s largest organSkin (integument) is body’s largest organ• Approximately 1.6 to 1.9 mApproximately 1.6 to 1.9 m22 in average-sized adult in average-sized adult• Integumentary system describes the skin Integumentary system describes the skin

and its appendages—the hair, nails, and and its appendages—the hair, nails, and skin glandsskin glands

• Thin and thick skinThin and thick skin– ““Thin skin”—covers most of body surface Thin skin”—covers most of body surface

(1 to 3 mm thick)(1 to 3 mm thick)

– ““Thick skin”—soles and palms Thick skin”—soles and palms (4 to 5 mm thick)(4 to 5 mm thick)

Anatomy of Skin

Functions of Skin

Function of Integumentary System

A. Regulation of Body Temperature

B. Protection from Dehydration and Infection

C. Respond to Temperature, Pressure, Pain

D. Excretion of Water, Salts, Urea (nitrogenous waste)

E. Synthesis Vitamin D (essential for Ca + P absorption)

F. First Defensive Barrier of Immune Response

Functions of the Skin

• ProtectionProtection– Physical barrier to microorganismsPhysical barrier to microorganisms– Barrier to chemical hazardsBarrier to chemical hazards– Reduces potential for mechanical traumaReduces potential for mechanical trauma– Prevents dehydrationPrevents dehydration– Protects (via melanin) excess UV exposureProtects (via melanin) excess UV exposure


• SensationSensation– Skin acts as a sophisticated sense organSkin acts as a sophisticated sense organ– Somatic sensory receptors detect stimuli that Somatic sensory receptors detect stimuli that

permit us to detect pressure, touch, permit us to detect pressure, touch, temperature, pain, and other general temperature, pain, and other general sensationssensations


• FlexibilityFlexibility– Skin is supple and elastic, thus permitting Skin is supple and elastic, thus permitting

change in body contours without injurychange in body contours without injury

• ExcretionExcretion– WaterWater– Urea/ammonia/uric acidUrea/ammonia/uric acid


• Hormone (Vitamin D) productionHormone (Vitamin D) production– Exposure of skin to UV light converts Exposure of skin to UV light converts

7-dehydrocholesterol to cholecalciferol— 7-dehydrocholesterol to cholecalciferol— a precursor to vitamin Da precursor to vitamin D

– Blood transports precursor to liver and Blood transports precursor to liver and kidneys, where vitamin D is producedkidneys, where vitamin D is produced

– Process and end result fulfill the necessary Process and end result fulfill the necessary steps required for vitamin D to be classified as steps required for vitamin D to be classified as a hormonea hormone


• ImmunityImmunity– Phagocytic cells destroy bacteriaPhagocytic cells destroy bacteria– Langerhans cells trigger helpful immune Langerhans cells trigger helpful immune

reaction working with “helper T cells”reaction working with “helper T cells”


– Heat lossHeat loss• approximately 80% of heat loss occurs approximately 80% of heat loss occurs

through the skin; remaining 20% occurs through the skin; remaining 20% occurs through the mucosa of the respiratory, through the mucosa of the respiratory, digestive, and urinary tractsdigestive, and urinary tracts

Layers of Skin

• Epidermis• Dermis• Subcutaneous layer• beneath dermis • not part of skin

Epidermis

• Lacks blood vessels• Keratinized• Thickest on palms and soles (0.8-1.4mm)• Melanocytes provide melanin• Rests on basement membrane• Stratified squamous

Structure of the Skin

• EpidermisEpidermis– Cell typesCell types

• Keratinocytes—Keratinocytes— constitute over 90% of cells present; constitute over 90% of cells present; principal structural element of the outer skinprincipal structural element of the outer skin

• Melanocytes—Melanocytes— pigment-producing cells (5% of the total); pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet lightcontribute to skin color; filter ultraviolet light

• Langerhans cells—Langerhans cells— dendritic (branched) antigen-presenting dendritic (branched) antigen-presenting cells (APCs), they play a role in immune responsecells (APCs), they play a role in immune response

Epidermis

Layers of Epidermis• stratum corneum• stratum lucidum• stratum granulosum• stratum spinosum• stratum basale


• EpidermisEpidermis– Cell layersCell layers

• Stratum germinativum (growth layer)—Stratum germinativum (growth layer)— describes the stratum spinosum and stratum describes the stratum spinosum and stratum basale togetherbasale together

– Stratum basale (base layer)—Stratum basale (base layer)—single layer of single layer of columnar cells; only these cells undergo mitosis, then columnar cells; only these cells undergo mitosis, then migrate through the other layers until they migrate through the other layers until they are shed are shed

– Stratum spinosum (spiny layer)—Stratum spinosum (spiny layer)—cells arranged in 8 cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNAshapes; cells rich in RNA


– Cell layersCell layers• Stratum granulosum (granular layer)—Stratum granulosum (granular layer)—cells cells

arranged in two to four layers and filled with arranged in two to four layers and filled with keratohyalin granules; contain high levels of keratohyalin granules; contain high levels of lysosomal enzymes lysosomal enzymes

• Stratum lucidum (clear layer)—Stratum lucidum (clear layer)—cells filled with cells filled with keratin precursor called keratin precursor called eleidin;eleidin; absent in thin skin absent in thin skin

• Stratum corneum (horny layer)Stratum corneum (horny layer)—most superficial —most superficial layer; dead cells filled with keratin (barrier area)layer; dead cells filled with keratin (barrier area)


• Dermal-epidermal junctionDermal-epidermal junction– A definite A definite basement membrane, basement membrane,

specialized fibrous elementsspecialized fibrous elements, and a , and a polysaccharide gel serve to polysaccharide gel serve to “glue” the “glue” the epidermis to the dermis belowepidermis to the dermis below

– The junction serves as The junction serves as a partial barrier a partial barrier to to the passage of some cells and large the passage of some cells and large moleculesmolecules


• DermisDermis– Sometimes called “true skin”—much thicker Sometimes called “true skin”—much thicker

than the epidermis and lies beneath itthan the epidermis and lies beneath it– Gives strength to the skinGives strength to the skin– Serves as a reservoir area for storage of Serves as a reservoir area for storage of

water and electrolyteswater and electrolytes

Dermis

• Contains dermal papillae

• Binds epidermis to underlying tissues

• Irregular dense connective tissue

• On average 1.0-2.0mm thick

• Muscle cells• Nerve cell processes• Specialized sensory receptors• Blood vessels• Hair follicles• Glands


• DermisDermis– Contains various structures:Contains various structures:

• Arrector pili muscles and hair follicles Arrector pili muscles and hair follicles • Sensory receptors Sensory receptors • Sweat and sebaceous glandsSweat and sebaceous glands• Blood vesselsBlood vessels

– Rich vascular supply plays a critical role in Rich vascular supply plays a critical role in temperature regulationtemperature regulation


• Dermis Dermis – Layers of dermis:Layers of dermis:

• Papillary layer—Papillary layer— composed of dermal papillae composed of dermal papillae that that project into the epidermisproject into the epidermis; contains fine ; contains fine collagenous and elastic fiberscollagenous and elastic fibers; contains the ; contains the dermal-epidermal junctiondermal-epidermal junction; forms a unique ; forms a unique pattern that gives pattern that gives individual fingerprintsindividual fingerprints

• Reticular layer—Reticular layer— contains contains dense, interlacing dense, interlacing white collagenous fibers and elastic fiberswhite collagenous fibers and elastic fibers to to make the skin make the skin tough yet stretchabletough yet stretchable; when ; when processed from animal skin, produces processed from animal skin, produces leatherleather

Lines of Cleavage

• Tension lines in the skin identify the predominant orientation of collagen fiber bundles.

• Clinically and surgically significant because cuts can result in slow healing and increased scarring.

Subcutaneous Layer

• hypodermis

• loose connective tissue

• adipose tissue

• insulates

• major blood vessels


• Hypodermis Hypodermis – Also called subcutaneous layer or superficial Also called subcutaneous layer or superficial

fasciafascia– Deep to the dermis, forming connection Deep to the dermis, forming connection

between the skin and other structuresbetween the skin and other structures– Not part of the skinNot part of the skin

Skin Color

Genetic Factors• varying amounts of melanin• varying size of melanin granules• albinos lack melanin

Environmental Factors• sunlight• UV light from sunlamps• X rays• darkens melanin

Physiological Factors• dilation of dermal blood vessels• constriction of dermal blood vessels• accumulation of carotene• jaundice

Skin Color– Melanin

• Basic determinant of skin color is quantity, type, and distribution of Basic determinant of skin color is quantity, type, and distribution of melaninmelanin

– Beta carotene • (group of yellowish pigments from food) can also contribute to (group of yellowish pigments from food) can also contribute to

skin colorskin color

– Hemoglobin• color changes also occur as a result of changes in blood flow color changes also occur as a result of changes in blood flow

– Redder skin color when blood flow to skin increasesRedder skin color when blood flow to skin increases– Cyanosis—bluish color caused by darkening of hemoglobin Cyanosis—bluish color caused by darkening of hemoglobin

when it loses oxygen and gains carbon dioxide (Figure 6-9)when it loses oxygen and gains carbon dioxide (Figure 6-9)– Bruising can cause a rainbow of different colors to appear in Bruising can cause a rainbow of different colors to appear in

the skin the skin

– Other pigments• from cosmetics, tattoos, and bile pigments in jaundice cosmetics, tattoos, and bile pigments in jaundice

Basis of Skin Color• The color of skin and mucous membranes can provide The color of skin and mucous membranes can provide

clues for diagnosing certain problems, such asclues for diagnosing certain problems, such as

– JaundiceJaundice• yellowish color to skin and whites of eyesyellowish color to skin and whites of eyes• buildup of yellow bilirubin in blood from liver diseasebuildup of yellow bilirubin in blood from liver disease

– CyanosisCyanosis• bluish color to nail beds and skinbluish color to nail beds and skin• hemoglobin depleted of oxygen looks purple-bluehemoglobin depleted of oxygen looks purple-blue

– ErythemaErythema• redness of skin due to enlargement of capillaries in dermisredness of skin due to enlargement of capillaries in dermis• during inflammation, infection, allergy or burnsduring inflammation, infection, allergy or burns

Sebaceous glandsSebaceous glands• Secrete sebum—oily substance that keeps hair Secrete sebum—oily substance that keeps hair

and skin soft and pliant; prevents excessive water and skin soft and pliant; prevents excessive water loss from the skinloss from the skin

• usually associated with hair follicles• Lipid components have antifungal activityLipid components have antifungal activity• Simple, branched glandsSimple, branched glands• Found in dermis except in palms and solesFound in dermis except in palms and soles• Secretion increases in adolescence; may lead to Secretion increases in adolescence; may lead to

formation of pimples and blackheadsformation of pimples and blackheads

Skin glands

Sweat Glands

• Widespread in skin

• Originates in deeper dermis Or hypodermis

• Eccrine glands

• Apocrine glands

• Ceruminous glands

• Mammary glands

• Eccrine glandsEccrine glands

–Most numerous sweat glands; quite smallMost numerous sweat glands; quite small–Distributed over total body surface with Distributed over total body surface with

exception of a few small areasexception of a few small areas–Simple, coiled, tubular glandsSimple, coiled, tubular glands–Function throughout lifeFunction throughout life–Secrete perspiration or sweat; eliminate Secrete perspiration or sweat; eliminate

wastes; and help maintain a constant wastes; and help maintain a constant core temperaturecore temperature

Sweat glands

• Apocrine glandsApocrine glands

–Located deep in subcutaneous layerLocated deep in subcutaneous layer–Limited distribution—axilla, areola of Limited distribution—axilla, areola of

breast, and around anusbreast, and around anus–Large (often more than 5 mm in diameter)Large (often more than 5 mm in diameter)–Simple, branched, tubular glandsSimple, branched, tubular glands–Begin to function at pubertyBegin to function at puberty–Secretion shows cyclic changes in female Secretion shows cyclic changes in female

with menstrual cyclewith menstrual cycle

Sweat glands

Hair

• Distribution—over entire body except Distribution—over entire body except palms of hands and soles of feet and a palms of hands and soles of feet and a few other small areasfew other small areas

• Fine and soft hair coat present before birth called Fine and soft hair coat present before birth called lanugolanugo

• Coarse pubic and axillary hair that develops at Coarse pubic and axillary hair that develops at puberty called puberty called terminal hairterminal hair

Functions of Hair

• Protection • Heat retention • Prevents the loss of conducted heat from the

scalp to the surrounding air • Facial expression• Sensory reception • Visual identification • Chemical signal dispersal

Hair Follicles

• Epidermal cells• Tube-like depression• Extends into dermis• Hair root• Hair shaft• Hair papilla• Dead epidermal cells• Melanin• Arrector pili muscle

A. Shaft - projects above surface of epidermis

1. medulla - polyhedral cells with eleidin2. cortex - elongated cells with/out

pigment3. cuticle - outermost layer, like shingles

on roof B. Root - below epidermis, penetrates

into the dermis C. Hair Follicle - at the base a single

hair 1. external root sheath - basale and

spinosum extension2. internal root sheath - internal hair

cell layers3. bulb - base of hair cell4. papilla - in the bulb, provides

nourishment for hair5. matrix - origin of new hair cellsD. arrector pili - smooth muscle, cause

hair to risenerve bundle responds to touch

E. hair root plexuses

• ColorColor– result of different amounts, distribution, types of melanin in result of different amounts, distribution, types of melanin in

cortex of haircortex of hair

• GrowthGrowth– hair growth and rest periods alternate; hair on head averages 5 hair growth and rest periods alternate; hair on head averages 5

inches of growth per yearinches of growth per year

• Sebaceous glandsSebaceous glands– attach to and secrete sebum attach to and secrete sebum

(skin oil) into follicle(skin oil) into follicle

• Male pattern baldness results from combination of genetic Male pattern baldness results from combination of genetic tendency and male sex hormonestendency and male sex hormones

Appearance of hair

Hair Thinning and Baldness

• Alopecia – hair thinning in both sexes

• True, or frank, baldness – Genetically determined and sex-influenced

condition

Consist of epidermal cells converted to hard Consist of epidermal cells converted to hard keratinkeratin

– Nail body—visible part of each nailNail body—visible part of each nail– Root—part of nail in groove hidden by fold of Root—part of nail in groove hidden by fold of

skin, the cuticleskin, the cuticle– Lunula—moon-shaped white area nearest Lunula—moon-shaped white area nearest

rootroot

Nails

• Nail bed—layer of epithelium under nail bodyNail bed—layer of epithelium under nail body– contains abundant blood vesselscontains abundant blood vessels

• Appears pink under translucent nailsAppears pink under translucent nails• Growth—nails grow by mitosis of cells in stratum germinativum Growth—nails grow by mitosis of cells in stratum germinativum

beneath the lunula; average growth about 0.5 mm per week, or beneath the lunula; average growth about 0.5 mm per week, or slightly over 1 inch per yearslightly over 1 inch per year

Types of Burns• First-degreeFirst-degree

– only epidermis (sunburn)only epidermis (sunburn)

Types of Burns• Second-degree burn Second-degree burn

– destroys entire epidermis & part of dermis destroys entire epidermis & part of dermis – fluid-filled blisters separate epidermis & dermisfluid-filled blisters separate epidermis & dermis– epidermal derivatives are not damagedepidermal derivatives are not damaged– heals without grafting in 3 to 4 weeks & may scarheals without grafting in 3 to 4 weeks & may scar

Types of Burns

• Third-degree or full-thicknessThird-degree or full-thickness– destroy epidermis, dermis & epidermal derivativesdestroy epidermis, dermis & epidermal derivatives– damaged area is numb due to loss of sensory nervesdamaged area is numb due to loss of sensory nerves

1 essentials of human anatomy essentials of human anatomy skin

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