Transcript Chapter 6 Skin and its Appendages

Chapter 6
Skin 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
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Skin classified as a cutaneous membrane
Two primary layers:
epidermis
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) 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 the thickness
of the stratum corneum and result in callus
formation
• Normally 10% to 12% of all cells in stratum basale
enter mitosis daily