Chapter 6 Skin and its Appendages

1. Chapter 6Skin and its Appendages

2. Introduction • Skin (integument) is body’s largest organ • Approximately 1.6 to 1.9 m2 (17-20 ft2) • 0.05 - 0.3 cm thick • ~9 pounds...7 - 15% of Body Weight • Self-repairing and protective boundary • Integumentary system describes the skin and its appendages • Hair • Nails • skin glands

3. 20 Blood Vessels 65 Hairs & Hair Muscles 78 Nerves 78 Sensors for Heat 13 Sensors for Cold 160 Sensors for Pressure 100 Sebaceous/Oil Glands 1300 Nerve Endings 19,500,000 Cells 500,000 Cells Dying & Being Replaced One Square Inch Contains

4. Structure of the Skin • Cutaneous membrane • Two primary layers • Epidermis • Outermost, thinner layer • Epithelial layer • Dermis • Inner, thcker layer • Vascular connective tissue • Joined by dermal-epidermal junction (Figures 6-1 and 6-2) • Subcutaneous layer • Hypodermis (superficial fascia) • Fat and areolar tissue

5. Structure of the Skin • Thin Skin • Covers most of body surface • Refers to epidermal layer only • 0.5 – 5 mm thick • Thick Skin • Contains all five layers of epidermis • Stratum corneum is especially noticeable • Dermal papillae • No hair • Soles and palms • 4 to 5 mm thick

6. Figure 5.1

8. Structure of the Skin • Epidermis • Cell types • Keratinocytes • constitute over 90% of cells present • principal structural element of the outer skin • Filled with tough, fibrous protein called keratin • Arranged in layers • Most important cells in the epidermis

9. Structure of the Skin • Epidermis • Cell types • Melanocytes • pigment-producing cells (5% of the total) • contribute to skin color (melanin) • filter ultraviolet light

10. Structure of the Skin • Epidermis • Cell types • Langerhans cells • dendritic (branched) antigen-presenting cells (APCs) • play a role in immune response • Defense mechanism for the body • Originate in bone marrow • Trigger immune reactions, epidermal macrophages

11. Structure of the Skin • Epidermis (cont.) • Cell layers • Stratum germinativum (growth layer)—describes the stratum spinosum and stratum basale together • Stratum basale (base layer) • single layer of columnar cells • only these cells undergo mitosis, then migrate through the other layers until they are shed • Stratum spinosum (spiny layer) • cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny shapes • cells rich in RNA

12. Structure of the Skin • Cell layers (cont.) • Stratum granulosum (granular layer) • cells arranged in two to four layers and filled with keratohyalin granules • where keratinization begins • two to four layers deep • contain high levels of lysosomal enzymes • Stratum lucidum (clear layer) • cells filled with keratin precursor called eleidin • serves to block water penetration or loss • absent in thin skin • Stratum corneum (horny layer) • most superficial layer • dead cells filled with keratin (barrier area)

13. Structure of the Skin • Cell layers (cont.) • Stratum corneum (horny layer) • Dead squamous filled with keratin cells on the skin’s surface • Keratinocytes held together by desmosomes • Thick cell membranes resistant to chemical • Keratinization • Hyperkeratosis • Functions • Waterproofing • Protection from abrasion and penetration • Rendering the body relatively insensitive to biological, chemical, and physical assaults

14. Figure 5.2b

17. Quick Check • Identify the two main or primary layers of skin. What tissue type dominates each layer? • The terms thin and thick skin refer to which primary layer of skin? How do thin and thick skin differ? • Identify the two main cell types found in the epidermis. • List the five layers or strata of the epidermis.