Ch. 5 The Integumentary System

Introduction Integument consists of: Skin Skin – largest organ Accessory structures (hair/sweat glands) Subcutaneous tissue Skin Barrier to many harmful substances

The Skin 2 major layers (Fig. 5-1) Epidermis – outer layer Dermis – inner layer

Epidermis Stratified squamous keratinizing epithelium Thickest on palms, soles Abundant keratinocytes No capillaries 2 sublayers inner stratum germinativum outer 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 Germinativum Keratinocytes living cells that synthesize antimicrobial “defensins” rupture pathogen membranes as part of inflammatory process Living portion produces vitamin D when exposed to sunlight

Stratum Corneum Outermost epidermal layer Keratin prevents evaporation and water entry Barrier to pathogens & chemicals

Langerhans Cells “dendritic cells” (Fig. 5-2) Originate in red bone marrow Phagocytize foreign material migrate to lymph nodes; take pathogen to lymphocytes triggers immune response

Melanocytes See Fig. 5-2 Produce melanin those with darker skin produce large amounts production increased in when exposed to UV rays Melanin gives color to hair, iris, choroid layer of eye See Table 5-1

Dermis Made 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 structures hair & nail follicles, sensory receptors, glands

Hair Follicles Made of epidermal tissue Base of follicle (Fig. 5-3) Hair root; mitosis occurs in matrix Produce keratin Get color from melanin Die & become incorporated into hair shaft Hair shaft pushed toward skin surface

Hair Follicles Eyelashes & eyebrows keep dust & sweat out of eyes Nostril hairs keep dust from entering nasal cavities Hair on head provides insulation body hair doesn’t serve this purpose Pilomotor (arrector pili muscle) attached to each follicle pull hair follicles upright (fear, cold)

Nail Follicles On ends of fingers & toes Produce nails; mitosis in nail root at the nail’s base (Fig. 5-4) New cells produce keratin & die Nail is dead keratin cells, but nail bed is alive

Nails Protect fingers & toes from mechanical injury Allow dexterity Good for scratching

Receptors Cutaneous senses Specific receptor for each sensation touch, pressure, heat, cold, pain Specific receptor for each sensation Receptors & sensation provide CNS with information about external environment

Glands Made of epithelial tissue (Fig. 5-1) Sebaceous glands Secrete sebum (oil) inhibits bacterial growth on skin’s surface prevents drying of skin, hair Ceruminous glands in the dermis of ear canals secrete cerumen (ear wax) keeps outer surface of eardrum pliable; prevents drying

Glands Sweat glands 2 types Apocrine – numerous in axillae (underarm), genital areas Eccrine – numerous on forehead, upper lip, palms, soles

Blood Vessels Capillaries in dermis Arterioles Smooth muscle in walls permits constriction or dilation maintains body temp.

Subcutaneous Tissue “superficial fascia” Made of areolar and adipose tissue Connects dermis to underlying muscles Secondary line of defense

Aging & The Integumentary System Skin layers become thinner, more fragile Fibroblasts die & are not replaced Repair of breaks or cuts slows Skin wrinkles Glands become less active Skin becomes dry Temp. regulation becomes harder Hair thins, turns white