Chapter 6 Skin and its Appendages Introduction Skin

Chapter 6 Skin and its Appendages

Introduction • Skin (integument) is body’s largest organ • Approximately 1. 6 to 1. 9 m 2 in average-sized adult • Integumentary system describes the skin and its appendages—the hair, nails, and skin glands

Structure of the Skin • • 1) 2) • Skin classified as a cutaneous membrane Two primary layers: epidermis Hypodermis lies beneath dermis

Structure of the Skin • Thin and thick skin – “Thin skin”—covers most of body surface (1 to 3 mm thick) – “Thick skin”—soles and palms (4 to 5 mm thick)

Epidermis – Three Cell types: • Keratinocytes—constitute over 90% of cells present; principal structural element of the outer skin • Melanocytes—pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet light • Langerhans cells—dendritic (branched) antigenpresenting cells (APCs), they play a role in immune response

Cell Layers • There are 6 layers to your epidermis: 1) Stratum germinativum (growth layer) 2) Stratum basale (base layer) 3) Stratum spinosum (spiny layer) 4) Stratum granulosum (granular layer) 5) Stratum lucidum (clear layer) 6) Stratum corneum (horny layer)

Structure of the Skin • Stratum germinativum (growth layer)— describes the stratum spinosum and stratum basale together

Structure of the Skin Stratum basale (base layer)—single layer of columnar cells; only these cells undergo mitosis, then migrate through the other layers until they are shed

Structure of the Skin – 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 • Stratum granulosum (granular layer)—cells arranged in two to four layers and filled with keratohyalin granules; contain high levels of lysosomal enzymes

Structure of the Skin • Stratum lucidum (clear layer)—cells filled with keratin precursor called eleidin; absent in thin skin

Structure of the Skin • Stratum corneum (horny layer)—most superficial layer; dead cells filled with keratin (barrier area)

Epidermal growth and repair • Turnover or regeneration time refers to time required for epidermal cells to form in the stratum basale and migrate to the skin surface—about 35 days • Shortened turnover time will increase thickness of the stratum corneum and result in callus formation • Normally 10% to 12% of all cells in stratum basale enter mitosis daily