anatomy of the skin rich callahan mspa, pa-c icm i summer 2009
TRANSCRIPT
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Anatomy of the Skin
Rich Callahan MSPA, PA-C
ICM I
Summer 2009
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Before Pathophysiology Comes Anatomy
• One of the keys to your knowledge of skin disease is understanding the anatomy of the skin and the particular way a given skin disease affects it.
• Anatomy of skin also important during dermatologic procedures like skin biopsy, excisions and ED&C.
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Skin Anatomy – Basic Overview
• Skin essentially composed of 3 layers: epidermis, dermis and subcutis (subcutaneous tissue.)
• Epidermis is outermost layer – primarily functional and protective. Subdivided into five layers which migrate upwards and whose purpose is ultimately to form the end layer, or stratum corneum – the outer layer of dead cells that protects us from our environment. Process is called keratinization.
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The first function of skin is physical protection from the environment.
Protection From:• UV radiation• Physical trauma• Liquids (there is a reason we’re waterproof)• Dehydration• Sudden temperature shifts• Microbes
First line of defense is the stratum corneum, which is primarily composed of laminated keratin.
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Definition of Keratin (From Taber’s Medical Dictionary)
• “A family of durable protein polymers that are found only in epithelial cells. They provide structural strength to skin, hair and nails. The fibrous protein is produced by keratinocytes.”
• Thoroughly understanding the process of keratinization which takes place in the epidermis will unlock answers for many skin diseases because so many of them are disorders of it.
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Keratin
• Comes from the Greek word “keras” for horn.
• The outer layer of epidermis, the stratum corneum, gets its name from the Latin word for horn.
• My first question was: Where were the people who make up these names seeing a horn?
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Perhaps it is because the phenomenon of cutaneous horn is the most overt keratinizing process
• Multiple underlying pathologies can cause a cutaneous horn:
• Verruca vulgaris (common wart)• Actinic Keratosis (AK)• Squamous Cell Carcinoma (SCC) • Seborrheic Keratosis (SK)• Psoriasis• Sometimes no underlying pathology is found
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Layers of the Epidermis: From Inside to Outside
Basal (bottom) layer: A single layer of cells arranged like columns – which divide and turn into the…
• Spinous layer (stratum spinosum)whose cells, keratinocytes, begin to form keratin, an insoluble protein critical in later stages.
• Granular layer (str. Granulosum) is where cells flatten out and stretch into the
• Stratum lucidum and eventually die to form the• Stratum corneum. Old school dermatologists called this
the “horny layer” (heh, heh.) Composed of laminated keratin.
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The “Horny Layer” huh? That term has largely been dropped in dermatology but is getting plenty of
utilization elsewhere…
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Dermis – Divided into 2 layers from top to bottom
• Superficial layer is the papillary dermis, a thin layer primarily of collagen fibers.
• Arranged in dome-shaped inclusions jutting into base of, and feeding small blood vessels into, the epidermis above.
• Deep layer is Reticular dermis – composed of thickly layered collagen fibers.
• Contains numerous small vessels, cutaneous nerves and apocrine glands.
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Subcutis – The Deepest Layer of skin (AKA superficial fascia or hypodermis)
• A layer of fat loosely marbled with connective tissue and the deeper parts of apocrine glands.
• Important route for small to medium-sized blood vessels, sensory and autonomic nerves, lymphatics.
• Deep to this is the deep fascia then skeletal muscle.
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