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: epidermis : keratinized stratified squamous epithelium dermis: Epidermal derivatives : hairs, nails, and sebaceous and sweat glands. 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. HYPODERMIS (Subcutaneous tissue). It is NOT the part of skin

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

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

Stratum basale / stratum germinativum Single layer of Columnar or Cuboidal cells Rests 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

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

keratohyalin + tonofilament = keratin 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

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

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).

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; ④ desmosomes:↓ ⑤ Mitotic action ↓

thin skin (eyelids): Stratum granulosum Thickness of epidermis thick skin (palms and soles):well-developed stratum corneum. lacks hair follicles and sebaceous glands. thin skin (eyelids): Stratum granulosum and lucidum less-developed ;but hair follicles and sebaceous glands well-developed.

NON KERATINIZED CELLS MELANOCYTES 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.

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

antigen presenting cell in skin involve in immune reaction 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

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?)

Structure related dermal protective function 1. Cornified layer--dried dead cell, full of wear-resisting keratin. 2. lamellated granules(Stratum granulosum )-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

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

thin in the eyelid thick over the back. 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.

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

SKIN APPENDAGES Hairs sebaceous sweat glands Nails 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

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

hair shaft hair root epithelial root sheath ct sheath hair papilla

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)

2. Sebaceous gland periphery– smaller, immature cell ; 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.

arrector pili

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 hormones when acted upon by bacteria, give a characteristic odour of sweat

汗腺导管 canal of sweat gland

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

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