Chapter 6 Skin and its Appendages

Introduction 0.05 - 0.3 cm thick 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

One Square Inch Contains 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

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

Structure of the Skin Thin Skin Thick 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

Figure 5.1

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

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

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

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

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)

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

Figure 5.2b

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.