1. Skin ---skin is the largest organ of the body, it constitutes about 16% of body weight ---its total surface area is about 1.2- 2.2 m 2 ---function: protection, sensory reception, excretion and thermoregulation

2. 1. Structure of skin Composed of 2 layers A) Epidermis (outer Epi.) B) Dermis (inner CT)

3. 1) epidermis ---keratinised stratified squamous epithelium ---consist of keratinised cell and non- keratinised cell

4. ① keratinised cell: ---from basal to surface, we can classify the cells into 5 layers ---from basal to surface, we can classify the cells into 5 layers

5. a. stratum basale (basal layer) ---structure: ---structure: LM: -a layer of cuboidal or low columnar cell with a large, pale N -basophilic cytoplasm -basophilic cytoplasm EM: -free ribosome -keratin filament- tonofilament -keratin filament- tonofilament -desmosome -desmosome ---function: mitotic activity and proliferation

6. b. stratum spinosum (spinous layer) ---structure: LM: -4-10 layers polygonal cell with large round nucleus -spinous processes -spinous processes -slight basophilic cytoplasm -slight basophilic cytoplasm EM: -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

7. c. stratum granulosum (granular layer) ---structure: LM: -3-5 layers flattened cell -muclei begin to degenerate-stained slightly -muclei begin to degenerate-stained slightly -keratohyalin granules: basophilic -keratohyalin granules: basophilic EM: -keratohyalin granules: with tonofilament insert into them -lamellated granules: fused with cell membrane -lamellated granules: fused with cell membrane * keratohyalin + tonofilament = keratin

8. d. stratum lucidum (clear layer) d. stratum lucidum (clear layer)---structure:LM: -3-4 layers of cell appear homogeneous and transparent -3-4 layers of cell appear homogeneous and transparent -no nucleus and organella -no nucleus and organella -eosinophilic-keratohyalin -eosinophilic-keratohyalin -tonofilament embedded in homogeneous matrix -tonofilament embedded in homogeneous matrix

9. e. stratum corneum (cornified layer) ---structure: LM: -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 outer surface

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

11. ---function: responsible for skin color responsible for skin color absorb ultraviolet light absorb ultraviolet light protect deep tissue protect deep tissue

14. b. Langerhans cell ---structure: LM: -deep nucleus, light cytoplasms LM: -deep nucleus, light cytoplasms -among the spinous cell -among the spinous cell -dendritic-typed processes -dendritic-typed processes EM: -lysosome EM: -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: antigen presenting cell in skin antigen presenting cell in skin involve in immune reaction involve in immune reaction

15. c. Merkel’s cell ---structure: ---structure: located in basal layer located in basal layer with short processes with short processes contain many dense-core granules contain many dense-core granules chemical synapse: between Merkel’s cell and afferent N chemical synapse: between Merkel’s cell and afferent N ---function: not very clear, may be sensory epithelial cell sensory epithelial cell neuroendocrine cell ( APUD, amine precursor uptake and decarboxylation cell) neuroendocrine cell ( APUD, amine precursor uptake and decarboxylation cell)

16. 2) Dermis: DCT ---papillary layer: dermal papillae- increase the junction between epi. and underlying CT capillary papillae capillary papillae nervous papillae nervous papillae

17. ---reticular layer: DCT, contains rough F-CF, EF, RF large BV, LV large BV, LV NE: lamellar corpuscle NE: lamellar corpuscle skin appendages: including sweat gland, sebaceous gland and hair skin appendages: including sweat gland, sebaceous gland and hair

18. 2. hypodermis: LCT and fat tissue

19. 3. skin appendages

20. 1) hair

21. 2) sebaceous gland

22. 3) sweat glands

24. 4) Nails