SkinSkin------skin is the largest organ of the body, skin is the largest organ of the body,

it constitutes about 16% of body it constitutes about 16% of body weightweight

------its total surface area is about 1.2-2.2 its total surface area is about 1.2-2.2 mm22

---function---function: protection, sensory : protection, sensory reception, excretion and reception, excretion and thermoregulationthermoregulation

1.1. Structure of skinStructure of skin

Composed of 2 layersComposed of 2 layers

A) A) EpidermisEpidermis (outer Epi.) (outer Epi.)

B) B) DermisDermis (inner CT) (inner CT)

1) 1) epidermisepidermis---keratinised stratified squamous epitheli---keratinised stratified squamous epitheli

umum---consist of keratinised cell and non-kerat---consist of keratinised cell and non-kerat

inised cellinised cell

①①keratinised cellkeratinised cell: : ---from basal to surf---from basal to surf

ace, we can classace, we can classify the cells into 5 ify the cells into 5 layerslayers

a.a. stratum basale stratum basale (basal layer) (basal layer) ---structure: ---structure: LM: -a layer of cuboidal or low columnar cell LM: -a layer of cuboidal or low columnar cell

with a large, pale Nwith a large, pale N -basophilic cytoplasm-basophilic cytoplasmEM: -free ribosomeEM: -free ribosome -keratin filament- tonofilament-keratin filament- tonofilament -desmosome-desmosome---function: mitotic activity and proliferation---function: mitotic activity and proliferation

b. b. stratum spinosumstratum spinosum (spinous layer) (spinous layer)---structure: ---structure: LM: -4-10 layers polygonal cell with large rounLM: -4-10 layers polygonal cell with large roun

d nucleusd nucleus -spinous processes-spinous processes -slight basophilic cytoplasm -slight basophilic cytoplasm EM: -tonofibrilsEM: -tonofibrils -lamellated granules:-lamellated granules: /100-300nm membrane-coated/100-300nm membrane-coated /contain phospholipid and steroid/contain phospholipid and steroid -intercellular bridges- Desmosome-intercellular bridges- Desmosome

c. c. stratum granulosumstratum granulosum (granular layer) (granular layer)---structure: ---structure: LM: -3-5 layers flattened cellLM: -3-5 layers flattened cell -muclei begin to degenerate-stained slightly-muclei begin to degenerate-stained slightly -keratohyalin granules: basophilic-keratohyalin granules: basophilicEM: -keratohyalin granules: with tonofilament iEM: -keratohyalin granules: with tonofilament i

nsert into themnsert into them -lamellated granules: fused with cell membr-lamellated granules: fused with cell membr

aneane* keratohyalin + tonofilament = keratin* keratohyalin + tonofilament = keratin

d. d. stratum lucidumstratum lucidum (clear layer) (clear layer)---structure:---structure:LM: LM: -3-4 layers of cell appear homogeneous and tr-3-4 layers of cell appear homogeneous and tr

ansparentansparent -no nucleus and organella-no nucleus and organella -eosinophilic-keratohyalin-eosinophilic-keratohyalin -tonofilament embedded in homogeneous ma-tonofilament embedded in homogeneous ma

trixtrix

e. e. stratum corneumstratum corneum (cornified layer) (cornified layer)---structure: ---structure: LM: -several layers horny cellLM: -several layers horny cell -died cell- no nucleus and organella-died cell- no nucleus and organella -eosinophilic-eosinophilic -keratin-keratin* desquamation: surface keratin will shed from o* desquamation: surface keratin will shed from o

uter surfaceuter surface

② ② non-keratinised cellnon-keratinised cell:: a. a. melanocytemelanocyte: : ---structure: ---structure: LM: -large cell with long branchesLM: -large cell with long branches -located among stratum basale cells -located among stratum basale cells EM: -risosomeEM: -risosome -RER-RER -Golgi complexes tyrosine-Golgi complexes tyrosine -melanosome(tyrosinase) →↓-melanosome(tyrosinase) →↓ ↓ ↓ melaninmelanin melanin granulesmelanin granules

------functionfunction: : responsible for skin colorresponsible for skin color absorb ultraviolet lightabsorb ultraviolet light protect deep tissueprotect deep tissue

b. b. Langerhans cellLangerhans cell---structure: ---structure: LM: -deep nucleus, light cytoplasmsLM: -deep nucleus, light cytoplasms -among the spinous cell-among the spinous cell -dendritic-typed processes-dendritic-typed processes EM: -lysosomeEM: -lysosome -Birbeck granule:-Birbeck granule: /membrane-coated/membrane-coated /15-30 nm long, 4 nm in D/15-30 nm long, 4 nm in D---function: ---function: antigen presenting cell in skinantigen presenting cell in skin involve in immune reactioninvolve in immune reaction

c. c. Merkel’s cellMerkel’s cell ---structure: ---structure: located in basal layerlocated in basal layer with short processeswith short processes contain many dense-core granulescontain many dense-core granules chemical synapse: between Merkel’s cell chemical synapse: between Merkel’s cell

and afferent Nand afferent N---function: not very clear, may be---function: not very clear, may be sensory epithelial cellsensory epithelial cell neuroendocrine cell ( APUD, amine precurneuroendocrine cell ( APUD, amine precur

sor uptake and decarboxylation cell)sor uptake and decarboxylation cell)

2) 2) DermisDermis: DCT: DCT------papillary layerpapillary layer: dermal papillae-incr: dermal papillae-incr

ease the junction between epi. and unease the junction between epi. and underlying CTderlying CT

capillary papillaecapillary papillae nervous papillaenervous papillae

------reticular layerreticular layer: :

DCT, contains rough F-CF, EF, RFDCT, contains rough F-CF, EF, RF large BV, LVlarge BV, LV NE: lamellar corpuscleNE: lamellar corpuscle skin appendages: including sweat skin appendages: including sweat

gland, sebaceous gland and hairgland, sebaceous gland and hair

2. 2. hypodermishypodermis: LCT and fat : LCT and fat tissuetissue

3. 3. skin appendagesskin appendages

1) 1) hairhair

2) 2) sebaceous glandsebaceous gland

3) 3) sweat glandssweat glands

4)4) NailsNails