Ch. 5 The Integumentary System

IntroductionIntegument consists of:

Skin – largest organAccessory structures (hair/sweat glands)Subcutaneous tissue

SkinBarrier to many harmful substances

The Skin2 major layers (Fig. 5-1)

Epidermis – outer layerDermis – inner layer

EpidermisStratified squamous keratinizing epitheliumThickest on palms, solesAbundant keratinocytesNo capillaries2 sublayers

inner stratum germinativumouter stratum corneum

Stratum Germinativum“stratum basale”Base of the epidermis where mitosis occurs

older cells pushed toward skin surface produce keratin and die

Merkel cells (Merkel discs)touch receptors (Fig. 5-2)

Stratum GerminativumKeratinocytes

living cells that synthesize antimicrobial “defensins” rupture pathogen membranes as part of

inflammatory processLiving portion produces vitamin D when

exposed to sunlight

Stratum CorneumOutermost epidermal layerKeratin prevents evaporation and water entryBarrier to pathogens & chemicals

Langerhans Cells“dendritic cells” (Fig. 5-2)Originate in red bone marrowPhagocytize foreign material

migrate to lymph nodes; take pathogen to lymphocytes triggers immune response

MelanocytesSee Fig. 5-2Produce melanin

those with darker skin produce large amountsproduction increased in when exposed to UV

raysMelanin gives color to hair, iris, choroid layer

of eyeSee Table 5-1

DermisMade of irregular fibrous connective tissue

fibroblasts produce collagen & elastic fibers allow strength & elasticity

Papillary layer – junction of dermis with epidermis (Fig. 5-1)abundant capillaries

Accessory structureshair & nail follicles, sensory receptors, glands

Hair FolliclesMade of epidermal tissueBase of follicle (Fig. 5-3)

Hair root; mitosis occurs in matrix1. Produce keratin 2. Get color from melanin3. Die & become incorporated into hair shaft4. Hair shaft pushed toward skin surface

Hair FolliclesEyelashes & eyebrows keep dust & sweat out

of eyesNostril hairs keep dust from entering nasal

cavitiesHair on head provides insulation

body hair doesn’t serve this purposePilomotor (arrector pili muscle) attached to

each folliclepull hair follicles upright (fear, cold)

Nail FolliclesOn ends of fingers & toesProduce nails; mitosis in nail root at the nail’s

base (Fig. 5-4)New cells produce keratin & dieNail is dead keratin cells, but nail bed is alive

NailsProtect fingers & toes from mechanical injuryAllow dexterityGood for scratching

ReceptorsCutaneous senses

touch, pressure, heat, cold, painSpecific receptor for each sensationReceptors & sensation provide CNS with

information about external environment

GlandsMade of epithelial tissue (Fig. 5-1)Sebaceous glands

Secrete sebum (oil) inhibits bacterial growth on skin’s surface prevents drying of skin, hair

Ceruminous glandsin the dermis of ear canalssecrete cerumen (ear wax)

keeps outer surface of eardrum pliable; prevents drying

GlandsSweat glands

2 types Apocrine – numerous in axillae (underarm), genital

areas Eccrine – numerous on forehead, upper lip, palms,

soles

Blood VesselsCapillaries in dermisArterioles

Smooth muscle in walls permits constriction or dilation maintains body temp.

Subcutaneous Tissue“superficial fascia”Made of areolar and adipose tissueConnects dermis to underlying musclesSecondary line of defense

Aging & The Integumentary SystemSkin layers become thinner, more fragileFibroblasts die & are not replacedRepair of breaks or cuts slowsSkin wrinkles Glands become less activeSkin becomes dryTemp. regulation becomes harderHair thins, turns white