skin and it s appendages
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Skin and it’s Appendages
Hsiao, Hsiao-Sheng 5-4-2012
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Skin
- The largest organ
- Divided into two distinct layers
• dermis (mesoderm)
dermis
• epidermis (ectoderm) epidermis
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Epidermis
Contains four main cell types
- Keratinocytes : most abundant cell type in epidermis
- Melanocytes (neural crest cell)
- Merkel cells
- Langerhans cells
• produce keratin ( a tough fibrous protein)
• melanin
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Layers of Epidermis
Stratum basale (Stratum geminativum)
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
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Stratum basale (Stratum geminativum)
Stratum spinosum
Stratum granulosum
Stratum corneum
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Stratum basale (Stratum geminativum)
Stratum spinosum
Melanocytes
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Stratum basale (Stratum geminativum)
Stratum spinosum
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Stratum spinosum
- Exhibit numerous cytoplasmic processes or spines
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Keratohyaline granules Only in thick skin
e.g. palms and soles
Stratum granulosum
Stratum lucidum
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Stratum granulosum
Keratohyaline granules
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Stratum corneum
- The flattened, desiccated, anucleate cells
- Filled with keratin filaments
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Stratum corneum
- The flattened, desiccated, anucleate cells
- Filled with keratin filaments
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Junction of the epidermis and dermis
Dermal papillae
Epidermal ridges
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General sensory receptors are
- Divided into two groups
• Free nerve ending
• Encapsulated nerve ending
* Meissner’s corpuscle
* Pacinian corpuscle
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Meissner’s corpuscles
-Spiraling nerve ending surrounded by modified Schwann cells
-Occur in the dermal papillae
-Rapidly adapting receptors for light touch
-Occur in sensitive, hairless areas of the skin
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Pacinian corpuscles
-Single nerve ending surrounded by layers of flattened Schwann cells
-Occur in the deep portion of dermis
-Sensitive to deep pressure rapidly adapting receptors
Inner core
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Inner core
A single large
unbranched
non-myelinated
nerve fiber
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Appendages of Skin
• Hair follicle
• Nail
• Sweat gland
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Sweat glands
-widely distributed on body
-Secretory units and excretory units
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Myoepithelial cells Excretory unit
Secretory unit
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Secretory unit
Excretory unit
Myoepithelial cells
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Shalf
Root
Hair
- Flexible strand of dead, keratinized cells
- Hard keratin- tough and durable
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Hair follicle
- External root sheath from epidermis
- Internal root sheath from matrix cells
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Hair follicle
- Glassy membrane
- External root sheath
- Internal root sheath
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Hair follicle
- Glassy membrane
- External root sheath
- Internal root sheath
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Hair bulb
- Deep, expanded end of the hair follicle
Dermal papilla
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Dermal papilla
Hair matrix
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Sebaceous glands
- Occur over entire body- except palms and soles
- Secrete sebum; holocrine secretion
-Develop as outgrowths of the external root sheath
of the hair follicle
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Sebaceous glands
- Simple alveolar glands
- Acinar form
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Arrector pili muscle
- Boundle of smooth muscle
- Hair strands erect when arrector pili contracts
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Nail root
Nail fold
Nail matrix
Nail plate
Nail bed
Hyponychium
Lunula
Eponychium
Nail
- Scalelike modification of epidermis
- Made of hard keratin
- Parts of the nail
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Nail plate
Hyponychium
Nail fold
Nail root Nail matrix
Nail bed
Nail
Eponychium
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Nail plate
Nail bed