The Integumentary System

The Integumentary SystemIntegument is skinSkin and its appendages make up the integumentary systemA fatty layer (hypodermis) lies deep to itTwo distinct regionsEpidermisDermis

Functions of skinProtectionCushions and insulates and is waterproofProtects from chemicals, heat, cold, bacteriaScreens UVSynthesizes vitamin D with UVRegulates body heatPrevents unnecessary water lossSensory reception (nerve endings)

EpidermisKeratinized stratified squamous epitheliumFour types of cellsKeratinocytes deepest, produce keratin (tough fibrous protein)Melanocytes - make dark skin pigment melanin Merkel cells associated with sensory nerve endings Langerhans cells macrophage-like dendritic cellsLayers (from deep to superficial)Stratum basale or germinativum single row of cells attached to dermis; youngest cellsStratum spinosum spinyness is artifactual; tonofilaments (bundles of protein) resist tensionStratum granulosum layers of flattened keratinocytes producing keratin (hair and nails made of it also)Stratum lucidum (only on palms and soles)Stratum corneum horny layer (cells dead, many layers thick)

(see figure on next slide)

Epithelium: layers (on left) and cell types (on right)

RememberFour basic types of tissue

Epithelium epidermis just discussedConnective tissue - dermisMuscle tissueNervous tissue

DermisStrong, flexible connective tissue: your hideCells: fibroblasts, macrophages, mast cells, WBCsFiber types: collagen, elastic, reticularRich supply of nerves and vesselsCritical role in temperature regulation (the vessels)Two layers (see next slides)Papillary areolar connective tissue; includes dermal papillae Reticular reticulum (network) of collagen and reticular fibers

*Dermis layers

***Dermal papillae

Epidermis and dermis of (a) thick skin and (b) thin skin(which one makes the difference?)

Fingerprints, palmprints, footprintsDermal papillae lie atop dermal ridgesElevate the overlying epidermis into epidermal ridgesAre sweat films because of sweat poresGenetically determined

Flexion creasesDeep dermis, from continual folding

FibersCollagen: strength and resilienceElastic fibers: stretch-recoilStriae: stretch marksTension lines (or lines of cleavage)The direction the bundlesof fibers are directed The dermis is the receptive site for the pigment of tattoos

HypodermisHypodermis (Gk) = below the skinSubcutaneous (Latin) = below the skinAlso called superficial fasciafascia (Latin) =band; in anatomy: sheet of connective tissueFatty tissue which stores fat and anchors skin (areolar tissue and adipose cells)Different patterns of accumulation (male/female)

Skin colorThree skin pigmentsMelanin: the most importantCarotene: from carrots and yellow vegiesHemoglobin: the pink of light skinMelanin in granules passes from melanocytes (same number in all races) to keratinocytes in stratum basaleDigested by lysosomesVariations in colorProtection from UV light vs vitamin D?

Skin appendagesDerived from epidermis but extend into dermisIncludeHair and hair folliclesSebaceous (oil) glandsSweat (sudoiferous) glandsNails

NailsOf hard keratinCorresponds to hooves and clawsGrows from nail matrix

Hair and hair follicles: complexDerived from epidermis and dermisEverywhere but palms, soles, nipples, parts of genitalia

*arrector pili is smooth muscle*Hair papilla is connective tissue________________Hair bulb: epithelial cells surrounding papilla

Functions of hairWarmth less in man than other mammalsSense light touch of the skinProtection - scalpPartsRoot imbedded in skinShaft projecting above skin surfaceMake up of hair hard keratinThree concentric layersMedulla (core)Cortex (surrounds medulla)Cuticle (single layers, overlapping)

Types of hairVellus: fine, short hairsIntermediate hairs Terminal: longer, courser hairHair growth: averages 2 mm/weekActive: growingResting phase then shedHair lossThinning age relatedMale pattern baldnessHair colorAmount of melanin for black or brown; distinct form of melanin for redWhite: decreased melanin and air bubbles in the medullaGenetically determined though influenced by hormones and environment

Sebaceous (oil) glandsEntire body except palms and solesProduce sebum by holocrine secretionOils and lubricates

Sweat glandsEntire skin surface except nipples and part of external genitaliaPrevent overheating500 cc to 12 l/day! (is mostly water) Humans most efficient (only mammals have)Produced in response to stress as well as heat

Types of sweat glandsEccrine or merocrineMost numerousTrue sweat: 99% water, some salts, traces of wasteOpen through poresApocrineAxillary, anal and genital areas onlyDucts open into hair follicesThe organic molecules in it decompose with time - odorModified apocrine glandsCeruminous secrete earwaxMammary secrete milk

Disorders of the integumentary systemBurnsThreat to lifeCatastrophic loss of body fluidsDehydration and fatal circulatory shockInfectionTypesFirst degree epidermis: redness (e.g. sunburn)Second degree epidermis and upper dermis: blisterThird degree - full thicknessInfectionsSkin cancer

BurnsFirst-degree(epidermis only; redness)Second-degree(epidermis and dermis,with blistering)Third-degree(full thickness, destroying epidermis, dermis, often part of hypodermis)

Critical burnsOver 10% of the body has third-degree burns25 % of the body has second-degree burnsThird-degree burns on face, hands, or feetEstimate by rule of 9s

Tumors of the skinBenign, e.g. wartsCancer associated with UV exposure (also skin aging)Aktinic keratosis - premalignantBasal cell - cells of stratum basaleSquamous cell - keratinocytesMelanoma melanocytes: most dangerous; recognition:A - AsymmetryB - Border irregularityC - ColorsD - Diameter larger than 6 mm

Basal cell carcinomaSqaumous cell carcinomaMelanoma Skin Cancer