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Chapter 11 skin

Chapter 11 skin. General structure of the skin (Epidermis/Dermis/Hypodermis) Nonkeratinocyte melanocyte/Langerhans &Merkel cell Epidermal derivatives : hairs, nails, sebaceous and sweat glands . 1. General description. Function: 1. Protection from injuries

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Chapter 11 skin

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  1. Chapter 11 skin • General structure of the skin (Epidermis/Dermis/Hypodermis) • Nonkeratinocyte melanocyte/Langerhans &Merkel cell • Epidermal derivatives :hairs, nails, sebaceous and sweat glands.

  2. 1. General description Function: 1. Protection from injuries or microorganisms. 2. Sensitive organ (feeling pain, temperature, touch & pressure ). 3. Regulation the balance of water, electrolyte & temperature of body. epidermis: keratinized stratified squamous epithelium dermis: Epidermal derivatives : hairs, nails, and sebaceous and sweat glands. HYPODERMIS (Subcutaneous tissue). It is NOT the part of skin

  3. 2. Epidermis (1) Construction Keratinized stratified squamous epithelium Stratum basale keratinized Stratum spinosum cell (5 layers) Stratum granulosum Stratum lucidum Stratum corneum non- KeratinizedMelanocytes cell Langerhans cells Merkel cells

  4. ①keratinised cell: ---from basal to surface, reflect changes :keratinization↑; Mitotic action↓

  5. Stratum basale / stratum germinativum • Single layer of Columnar or Cuboidal cellsRests on the basement membrane by hemidesmosomes ; • Cytoplasm is BASOPHILIC (Ribosomes—synthesis of keratin) , Desmosomes (lateral surface),mitotic activity( stem cells) which diferentiate daughters and migrates upward to replace dead cells • Scatter MELANOCYTES & MERKEL CELLS

  6. Stratum spinosum • 4 – 10 layers of Polygonal cells with large nuclei • desmosomes ("spines"), tonofilaments development well Cytoplasm is BASOPHILIC (Many ribosomes) • Thick(thick skin,high friction areas), Contains langerhans cells

  7. Stratum granulosum  LM: 3-5 layers, spindle • degenerating nu. & organells • coarse & basophilic granules( no surrounded by membrane) --keratohyalin (phosphate groups) EM:lamellated granules--fused with cell membrane,produce a “cement” ----seals the skin to foreign objects & water keratohyalin + tonofilament = keratin

  8. Stratum lucidum • 3-4 layers and transparent • no nucleus and organella • eosinophilic-keratohyalin • More in thick skin

  9. Stratum corneum •  Cells of the cornified layer are dead, eventually sloughed • 15 – 20 layers in Thick skin,3 – 4 layers in Thin skin EM:full of keratin, thickened membrane, degenerated desmosomes (surface layers).

  10. CONCLUSION The changes of the keratinized cells from basal layer to cornified layer show the process of the keratinization: ①Morphology: Columner →polygonal→ flattened; basophilic→acidophilic ② Nu./ Organelle:↓ ③ keratin: ↑ Filaments: ↑ scattered→bundle; ④desmosomes:↓ ⑤Mitotic action↓

  11. Thickness of epidermis • thick skin (palms and soles):well-developed stratum corneum. lackshair follicles and sebaceous glands. • thin skin (eyelids): Stratum granulosum and lucidumless-developed ;but hair follicles and sebaceous glandswell-developed.

  12. NON KERATINIZED CELLSMELANOCYTES • Originates:neural crest • Located:stratum basale & hair follicles • LM:Irregular extension branches into the epidermis melanosomes containing tyrosinase. • Melanin protects the body against the harmful sun’s ultraviolet rays. • Skin Colour depends upon activity of these cells rather than number • Deficiency of Tyrosinase  ALBINISM (白化病) • most pigment-containing cells in the epidermis are normally keratinocytes rather than melanocytes.

  13. On exposure to sunlight, the enzyme TYROSINASE is activated  Increased melanin formation tyrosin melanosome(tyrosinase) →↓ ↓ melanin melanin granules

  14. LANGERHANS CELLS • derived Monocyte • Present in all layers but predominant in stratum spinosum • pale cytoplasm • Contains BIRBECK GRANULES ---function: • antigen presenting cell in skin • involve in immune reaction

  15. Merkel’s cell ---structure: • Seen in stratum basale near the hair follicles • short processes, dense-core granules • chemical synapse: between Merkel’s cell and afferent nerve ---function: not very clear, may be sensory epithelial (perception of stimulation / induce and regulate the growth of nerve fiber in skin?)

  16. Structure related dermal protective function 1. Cornified layer--dried dead cell, full of wear-resistingkeratin. 2. lamellated granules(Stratumgranulosum )-fused with cell membrane,seals the skin to foreign objects & water 3. Melanocyte----melanin, prevent ultraviolet radiation from damaging skin 4. Langerhans cells ------ immune defence

  17. DERMIS Papillary layer+Reticular layer • Papillary layer: LCT, tactile corpuscles are found • strengthening (more found friction ismore) touch feeling; nourishment.

  18. Reticular layer: • Irregular DCT • More elastic & collagen fibres (elasticity & toughness of skin) • Hair follicles, sweat & sebaceous glands are found • thin in the eyelid thick over the back.

  19. HYPODERMIS • loose connective tissue • Contains FAT TISSUE Excessive fat gets deposited in the hypodermis

  20. SKIN APPENDAGES • important in recovery scrapes and burns (epidermis removed a fairly large area,--- grow quickly from the epithelial cells in hair follicles and/or sweat glands.   • Third-degree burns :tissue damage extends deep enough into the dermis and destroy sources of replacement cells. • Hairs • sebaceous • sweat glands • Nails

  21. hair Sebaceous gland sweat gland hair papilla hair bulb 1. Hairhair shaft a strip of cornified cells hair root hair follicle

  22. hair shaft hair root epithelial root sheath ct sheath hair papilla

  23. arrector pilli muscle SHAFT: outside the epidermis cornified cells filled with Keratin ROOT:Implanted in the skin - Surrounded by a hair follicle, Hair bulb---stem cell Hair papilla(CT) – Nourishes HAIR MUSCLE (arrector pili): smooth muscle connecting dermal papilla and hair follicle Its contraction causes hair to become erect & the surrounding skin to rise (goose pimples)

  24. 2. Sebaceous gland secretory portion: periphery– smaller, immature cell ; centeral -- full of lipid droplet, excrete sebum by holocrine. Duct:shorter, open at the superior segment of hair follicle. Function:soften skin and kill bacteria.

  25. arrector pili

  26. 3、SWEAT GLANDS ECCRINE SWEAT GLANDS • secretory portion :simple cuboidal epithelium interspersed myoepithelial cells. • conducting portion: two-layered stratified cuboidal epithelium,  stained intensely. • APOCRINE SWEAT GLANDS • Distribute at armpit, areola of breast ，duct in secretory portion is thicker, open at hair follicle • Secretion is mainly protein controlled by sex hormoneswhen acted upon by bacteria, give a characteristic odour of sweat

  27. 汗腺导管 canal of sweat gland

  28. NAIL Horny plates on the distal parts of the dorsal surfaces of fingers & toes,keratinized epidermal cells Stratum corneum forms the Eponychium (指甲上皮 ) Nail plate rests on a Nail bed made up of stratum basale & stratum spinosum Nail root is embedded proximally in between the fold of skin on itself

  29. THE END

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