Chapter 6Skin and its Appendages

Introduction

• Skin (integument) is body’s largest organ• Approximately 1.6 to 1.9 m2 in

average-sized adult• Integumentary system describes the skin

and its appendages—the hair, nails, and skin glands

Structure of the Skin

• Skin classified as a cutaneous membrane• Two primary layers:1) epidermis 2) dermis• 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) antigen-presenting 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 the thickness of the stratum corneum and result in callus formation

• Normally 10% to 12% of all cells in stratum basale enter mitosis daily