The Integumentary The Integumentary System System (The Skin)(The Skin)

Anatomy & Physiology IChapter 6

Integumentary System – consists of the skin and its accessory organs◦ hair, nails, and cutaneous glands

most visible system and more attention paid to this organ system

skin is the most vulnerable organ◦ exposed to radiation, trauma, infection, and

injurious chemicalsdermatology – study and medical

treatment of the integumentary systeminspection of the skin, hair, and nails is

significant part of a physical exam

The Integumentary SystemThe Integumentary SystemThe Integumentary SystemThe Integumentary System

Skin and Subcutaneous Skin and Subcutaneous TissueTissuethe body’s largest and heaviest organ

◦ 15% of body weightconsists of two layers:

◦ epidermis – stratified squamous epithelium◦ dermis – connective tissue layer

hypodermis – another connective tissue layer below the dermis

thick skin – on palms and sole, and corresponding surfaces on fingers and toes◦ has sweat glands, but no hair follicles or

sebaceous (oil) glandsthin skin – covers rest of the body

◦ possesses hair follicles, sebaceous glands and sweat glands

Cross section of the skin.

EpidermisEpidermisepidermis – surface portion of the skin

keratinized stratified squamous epithelium◦dead cells at the surface packed with tough

protein – keratin◦lacks blood vessels; depends on the diffusion

of nutrients from underlying connective tissue

Stratum basale – deepest layer of epidermis

Stratum corneum – superficial layer of epidermis

Cells of EpidermisCells of Epidermisfive types of cells of the epidermis

◦ stem cells - undifferentiated cells that give rise to keratinocytes in deepest layer of epidermis (stratum basale)

◦ keratinocytes - synthesize keratin great majority of epidermal cells

◦ Melanocytes - synthesize pigment melanin that shields DNA from ultraviolet radiation occur only in stratum basale

◦ tactile (merkel) cells - touch receptor cells associated with dermal nerve fibers in basal layer of epidermis

◦ dendritic (langerhans) cells - macrophages originating in bone marrow that guard against pathogens that penetrate the skin

keratinocytes are produced deep in the epidermis by stem cells in stratum basale

mitosis requires an abundant supply of oxygen and nutrients◦ deep cells acquire from blood vessels in nearby

dermis

newly formed keratinocytes push the older ones toward the surface

in 30 - 40 days a keratinocyte makes its way to the skin surface and flakes off◦ slower in old age

◦ faster in skin injured or stressed calluses or corns – thick accumulations of dead

keratinocytes on the hands or feet

Life History of Life History of KeratinocytesKeratinocytes

Dermal blood vessels

Tactile cell

Melanocyte

Dead keratinocytes

Exfoliatingkeratinocytes

Living keratinocytes

Dendritic cell

Stem cell

Dermis

Stratum lucidum

Stratum basale

Stratum granulosum

Stratum spinosum

Stratum corneum

Sweat pore

Tactile nerve fiber

Dermal papilla

Sweat duct

Cell Types and Layers of the of the EpidermisCell Types and Layers of the of the Epidermis

Epidermal Water BarrierEpidermal Water Barrierepidermal water barrier - forms between

stratum granulosum and stratum spinosumconsists of:

◦ lipids secreted by keratinocytes

◦ tight junctions between keratinocytes

critical to retaining water in the body and preventing dehydration

cells above the water barrier quickly die◦ barrier cuts them off from nutrients below

◦ dead cells exfoliate (dander)

◦ dandruff – clumps of dander stuck together by sebum (oil)

DermisDermisdermis – connective tissue layer beneath the

epidermiscomposed mainly of collagen with elastic

fibers, reticular fiberswell supplied with blood vessels, sweat

glands, sebaceous glands, and nerve endingshair follicles and nail roots are embedded in

dermissmooth muscle (piloerector muscles)

associated with hair follicles◦ contract in response to stimuli, such as cold, fear,

and touch – goose bumps

DermisDermisdermal papillae – upward fingerlike extensions

of the dermis◦ friction ridges on fingertips that leave

fingerprints

The dermis has two layers:◦papillary layer (superficial) – thin layer of

areolar tissue; rich in small blood vessels

◦reticular layer – deeper and much thicker layer of dermis consists of dense, irregular connective tissue stretch marks – tears in the collagen fibers

caused by stretching of the skin due to pregnancy or obesity

Structure of the DermisStructure of the Dermis

Reticular layer of dermis

Papillary layer of dermis

Subcutaneous Layer: Subcutaneous Layer: HypodermisHypodermis(superficial fascia)(superficial fascia)

NOT a layer of skinbinds skin to underlying tissuesAdipose and areolar tissuepads bodyHighly vascular

◦ drugs introduced by injection quickly absorbed

subcutaneous fat◦ energy reservoir; thermal

insulation◦ 8% thicker in women

Nerves and nerve endings

Accessory Structures of Accessory Structures of the Skinthe SkinSome structures of the integumentary system protect the skin and have some more generalized functions as well

Cutaneous Glands Hair Nails

Cutaneous GlandsCutaneous Glands

the skin has five types of glands:

• Two types of sudoriferous glands:

― merocrine (eccrine) sweat glands

― apocrine sweat glands

• sebaceous glands

• ceruminous glands

• mammary glands

Sweat Glands (Sudoriferous)Sweat Glands (Sudoriferous)merocrine (eccrine) sweat glands

◦ most numerous skin glands◦ watery perspiration that helps cool the body

apocrine sweat glands ◦ develop at puberty; ducts lead to nearby hair

follicles◦ occur in groin, anal region, axilla, bearded area in

mature males◦ scent glands that respond to stress and sexual

stimulation◦ produce sweat that is thicker, milky, and contains

fatty acids◦ bromhidrosis - disagreeable body odor produced by

bacterial action on fatty acids

SweatSweatpotassium ions, urea, lactic acid, ammonia,

and some sodium chloride remain in the sweat, most sodium chloride reabsorbed by duct

some drugs are also excreted in sweat

on average, 99% water, with pH range of 4 to 6

◦ acid mantle – inhibits bacterial growth

insensible perspiration – 500 ml per day

◦ does not produce visible wetness of skin

diaphoresis – excessive sweating with wetness of the skin

◦ exercise – may lose one liter of sweat per hour

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Sebaceous GlandsSebaceous Glands

Produce a variety of secretions◦Sebum – oily secretion produced by sebaceous glands

◦Vernix caseosa - the waxy looking white substance that covers a newborn baby

◦Eye lubrication - Sties are formed because of bacterial infection in the Sebaceous glands of the eye.

short ducts opening into hair folliclekeeps skin and hair from becoming

dry, brittle, and crackedlanolin – sheep sebum

Ceruminous GlandsCeruminous Glandsfound only in external ear canal

their secretion combines with sebum and dead epithelial cells to form earwax (cerumen)◦keep eardrum pliable◦waterproofs the canal◦kills bacteria◦makes guard hairs of ear sticky to help

block foreign particles from entering auditory canal

Mammary GlandsMammary Glands

Men and women have mammary glands but they are underdeveloped in men

mammary glands – milk-producing glands that develop only during pregnancy and lactation◦ modified apocrine sweat gland◦ richer secretion released by ducts opening into the

nipple

HairHairComposed mainly of keratin and is not livingHair folliclesMelanocytesArrector pili

•Hair is divisible into three zones along its length– bulb – a swelling at the base where

hair originates in dermis or hypodermis• only living hair cells are in or near bulb

– root – the remainder of the hair in the follicle

– shaft – the portion above the skin surface

Portion of skin showing associated glands and hair

NailsNails

Made of keratin produced by cells that originate in the outer layer of the epidermisNail rootNail plateNail bedLunulaCuticle

Nail structure.

Functions of the SkinFunctions of the Skin

Four major functionsProtection against infectionProtection against dehydration

(drying)Regulation of body temperatureCollection of sensory information

Protection Against Protection Against InfectionInfection

Intact skin forms a primary barrier against invasion

Interlocking pattern resists penetration

Shedding removes pathogensProtects against bacterial toxinsProtects against some harmful

environmental chemicals

Protection Against Protection Against DehydrationDehydration

Skin prevents water loss by evaporation

Keratin in the epidermisSebum release from the

sebaceous glands

Regulation of Body Regulation of Body TemperatureTemperatureLoss of excess heat and protection from cold are important functions of the skinConstriction of blood vesselsDilation of blood vesselsEvaporation of perspiration

Collection of Sensory Collection of Sensory InformationInformation

Skin has many nerve endings and other special receptors

Free nerve endingsTouch receptors (Meissner

corpuscle)Deep pressure receptors

(Pacinian corpuscle)

Other Activities of the SkinOther Activities of the Skin

Absorption of substances such as medications

Excretion◦Water◦Electrolytes◦Wastes

Manufacture of vitamin D

ColorColorFactors that influence skin color

Amount of pigment in the epidermis

◦ Melanin

◦ Carotene

Quantity of blood circulating in superficial blood vessels

◦ Hemoglobin – pigment that gives blood its color

Composition of substances circulating in blood

◦ Oxygen

ColorColorFactors that influence skin color

Discoloration

◦ Pallor: pale skin, reduced blood flow

◦ Flushing: redness, as in fever

◦ Cyanosis: bluish color of skin; lack of oxygen in blood

◦ Yellow skin: jaundice, bilirubin in blood; carotenemia from excessive intake of carrots or other deeply colored vegetables

LesionsLesionsAny wound or local damage to tissueSurface lesions

◦ Macule – spot that is not raised or depressed◦ Papule – solid, raised lesion◦ Vesicle – fluid filled sac or blister◦ Pustule – a vesicle filled with pus

Deeper lesions◦ Excoriation – simple scratch◦ Laceration – rough; jagged wound formed

from tearing of the skin◦ Ulcer – sore associated with disintegration

and death of tissue◦ Fissure – a crack in the skin

BurnsBurns leading cause of accidental death

◦ fires, kitchen spills, sunlight, ionizing radiation, strong acids or bases, or electrical shock

◦ deaths result primarily from fluid loss, infection and toxic effects of eschar – burned, dead tissue debridement – removal of eschar

Categorized by Depth of damage

◦ Superficial partial-thickness◦ Deep partial-thickness◦ Full-thickness

Amount of body surface area (BSA) involved◦ Rule of nines◦ Lund and Browder method

BurnsBurnsclassified according to the depth of tissue

involvement◦ first-degree burns – partial thickness burn -

involve only the epidermis marked by redness, slight edema, and pain heal in a few days most sunburns are first degree burns

◦ second-degree burns – partial thickness burn - involve the epidermis and part of the dermis leaves part of the dermis intact red, tan, or white two weeks to several months to heal and may leave scars blistered and very painful

◦ third-degree burn – full thickness burn – the epidermis and all of the dermis, and often some deeper tissues (muscles or bones) are destroyed often require skin grafts needs fluid replacement and infection control

Degrees of Burn InjuriesDegrees of Burn Injuries

First degree Second degree

Partial-thickness burns

Third degree

Full-thickness burns

Tissue RepairTissue RepairWound healing Occurs only in areas with actively

dividing cells◦Epithelial tissues◦Connective tissues◦Minimally in muscle and nervous tissue

Is affected by◦Nutrition◦Blood supply◦Infection◦Age

Care of the SkinCare of the SkinProper nutritionAdequate circulationRegular cleansing

◦Removes dirt and dead skin◦Sustains slightly acid environment to

inhibit bacteriaProtection from sunlight

◦Exposure to UV light causes genetic mutations in skin that can lead to cancer, and causes premature aging.

Skin DisordersSkin Disorders

Range from superficial to deep-seated

DermatitisDermatitis

Inflammation of the skinDermatosis is any skin diseaseAtopic dermatitis

PsoriasisPsoriasis

Chronic, recurrent overgrowth of epidermis

Sharply outlined red (erythematous) areas

Flat areas (plaques) covered with silvery scales

A hereditary pattern sometimes present

Immune disorder may be involved

Skin CancerSkin Cancerskin cancer – induced by the ultraviolet

rays of the sun◦ most often on the head and neck◦ most common in fair-skinned people and the

elderly◦ the most common form of cancers in the US◦ one of the easiest to treat◦ has one of the highest survival rates if detected

and treated early◦ three types of skin cancer named for the

epidermal cells in which they originate◦ basal cell carcinoma, squamous cell carcinoma,

and malignant melanoma

Basal Cell CarcinomaBasal Cell Carcinoma

- most common type

- least dangerous because it seldom metastasizes

- forms from cells in stratum basale

- lesion is small shiny bump with central depression and beaded edges

Basal cell carcinoma

Squamous Cell CarcinomaSquamous Cell Carcinoma

- arise from keratinocytes from stratum spinosum

- lesions usually appear on scalp, ears, lower lip, or back of the hand

- have raised, reddened, scaly appearance later forming a concave ulcer

- chance of recovery good with early detection and surgical removal

- tends to metastasize to lymph nodes and may become lethal

Squamous cell carcinoma

Malignant Malignant MelanomaMelanoma

- skin cancer that arises from melanocytes often in a preexisting mole- less than 5% of skin cancers, but most deadly form- treated surgically if caught early- metastasizes rapidly - unresponsive to chemotherapy - usually fatal - person with metastatic melanoma lives only 6 months from diagnosis- 5% - 14% survive 5 years- greatest risk factor – familial history of malignant melanoma- high incidence in men, redheads, people who experience severe sunburn in childhood

Malignant melanoma

Acne and Other Skin Acne and Other Skin InfectionsInfectionsAcne

◦Sebaceous glands diseaseImpetigo

◦Staphylococcal or streptococcal originViral infections

◦Herpes simplex virus◦Herpes zoster virus (shingles)◦Human papillomavirus (HPV) (wart or

verruca)Fungal infections

◦Tinea or ringworm

Alopecia (Baldness)Alopecia (Baldness)

Factors that affect baldnessHeredity, aging, and male sex

hormones (male pattern baldness)

Systemic diseaseDrugs

Allergy and Other Immune Allergy and Other Immune DisordersDisorders

Often involve the skinAllergy—reaction to a substanceAutoimmune disorders—reaction

to one’s own tissues◦Pemphigus◦Lupus erythematosus◦Scleroderma

Pressure UlcersPressure Ulcers

Skin lesions that appear where the body rests on skin that covers bony projections.

Also known as decubitus ulcers or bedsores

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