Understanding the Skin: An In-depth Guide

1. Ch. 5 The Integumentary System

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

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

5. Epidermis • Stratified squamous keratinizing epithelium • Thickest on palms, soles • Abundant keratinocytes • No capillaries • 2 sublayers • inner stratum germinativum • outer stratum corneum

6. 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)

8. 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

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

10. 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

11. 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

12. 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

13. 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

15. 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 (arrectorpili muscle) attached to each follicle • pull hair follicles upright (fear, cold)

16. 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

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

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

20. 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

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

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

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

24. 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