Chapter 11 SkinChapter 11 Skin

---skin is the largest organ of the body, it ---skin is the largest organ of the body, it constitutes about 16% of body weightconstitutes about 16% of body weight

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

---function: protection, sensory reception, ---function: protection, sensory reception, excretion and thermoregulationexcretion and thermoregulation

1. Structure of skin1. Structure of skin

---epidermis---epidermis

---dermis---dermis

1) epidermis1) epidermis---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 fiify the cells into five layersve layers

a.a. stratum basalestratum basale ---structure: ---structure: LM: -a layer of cuboidal or low columnar cell with LM: -a layer of cuboidal or low columnar cell with

a large, pale Na 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---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---structure: ---structure: LM: -3-5 layers flattened cellLM: -3-5 layers flattened cell -muclei begin to degenerate-stained slightl-muclei begin to degenerate-stained slightl

yy -keratohyalin granules: basophilic-keratohyalin granules: basophilicEM: -keratohyalin granules: with tonofilament EM: -keratohyalin granules: with tonofilament

insert into theminsert into them -lamellated granules: fused with cell mem-lamellated granules: fused with cell mem

branebrane* keratohyalin + tonofilament = keratin* keratohyalin + tonofilament = keratin

d. d. stratum lucidumstratum lucidum---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. stratum corneume. stratum corneum---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

---function: ---function:

• 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. Merkel’s cellc. Merkel’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 layer: dermal papillae-incre---papillary layer: dermal papillae-incre

ase the junction between epi. and undase the junction between epi. and underlying CTerlying CT

• capillary papillaecapillary papillae• nervous papillaenervous papillae

---reticular layer: ---reticular 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. hypodermis: LCT and fat 2. hypodermis: LCT and fat tissuetissue

3. skin appendages3. skin appendages

1) hair1) hair

2) sebaceous gland 2) sebaceous gland

3) sweat glands 3) sweat glands