1. Skin Jun Zhou School of Medicine, Zhejiang University 20140325

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

3. skin epidermis (dermis) hypodermis 附属器官： 毛 皮脂腺 汗腺 指（趾）甲

4. Structure of skin Epidermis ( 表皮 ) Dermis ( 真皮 )

5. Epidermis --- consist of keratinised cell （角质形成细胞） non-keratinised cell （非角质形成细胞） ---keratinised stratified squamous epithelium

6. Keratinised cell  from basal to surface  five layers

7. stratum corneum （ C ） stratum lucidum （ L ） stratum granulosum （ G ） stratum spinosum （ S ） stratum basale （ B ） Epidermis

8. Thin skin Only has four layers: 1.Stratum corneum 2.Stratum granulosum 3.Stratum spinosum 4.Stratum basalis Dermis

9. stratum basale （ 基底层） ---structure: LM:  one layer, cuboidal or low columnar,  basophilic cytoplasm EM:  free ribosome  keratin filament 角蛋白丝 ( tonofilament 张力丝 )  desmosome ---function:  mitotic activity and proliferation

10. stratum spinosum （棘层） LM:  4-10 layers, polygonal cell  spinous processes  slight basophilic cytoplasm  Tonofibrils （张力原纤维） EM:  Keratin filament （角蛋白丝）  lamellated granules: /100-300nm membrane-coated /contain phospholipid and steroid  intercellular bridges- Desmosome

11. stratum granulosum （颗粒层） LM:  3-5 layers, flattened cell  nuclei begin to degenerate  keratohyalin granules （透明角质颗粒）  basophilic EM:  keratohyalin granules: with tonofilament insert into them  lamellated granules: fused with cell membrane  * keratohyalin + tonofilament = keratin （角质）

12. stratum lucidum （透明层） LM:  3-4 layers  homogeneous and transparent  no nucleus and organella  eosinophilic-keratohyalin  tonofilament embedded in homogeneous matrix lucidum

13. stratum corneum （角质层） LM:  several layers horny cell  died cell- no nucleus and organella  eosinophilic  keratin  * desquamation: surface keratin will shed from outer surface corneum lucidum

14. A. Melanocyte （黑色素细胞） : LM:  located among stratum basale cells  large cell with long branches EM:  ribosome  RER  Golgi complexes tyrosine -melanosome(tyrosinase) → ↓ ↓ melanin melanin granules Non-keratinised cell

15. Melanocytes 黑素細胞 Melanocytes Dermis Basal cells contain brown pigment

16. Function:  responsible for skin color  absorb ultraviolet light  protect deep tissue

17. B. Langerhans cell ---structure: LM:  Among the spinous cell  deep nucleus, light cytoplasms  dendritic-typed processes EM:  lysosome  Birbeck granule: /membrane-coated /15-30 nm long, 4 nm in D ---function:  antigen presenting cell in skin  involve in immune reaction

18. C. Merkel cell  located in basal layer  with short processes  contain many dense-core granules Function:  not very clear  may be sensory epithelial cell  neuroendocrine cell

19. Dermis DCT ---Papillary layer （乳头层） junction between epi. and underlying CT ---Reticular layer （网状层） DCT, BV, LV  lamellar corpuscle  skin appendages sweat gland, sebaceous gland and hair papillary layer reticular layer

20. Papillary layer 乳头层 Papillary layer (dermal papilla), contains fine collagen fibres, capillary network and nerves Spiraling duct of sweat gland through thick epidermis Dermal ridges determine the patterns of fingerprints; scientific basis of dermatoglyphics Epidermal ridge Dermal ridge

21. Hypodermis （皮下组织） LCT and fat tissue

22. skin appendages

23. Hair

24. Schematic diagram to show various parts and associated structures of hair follicle A B C D

25. Hair follicle Dermis Sebaceous gland Hair follicle Hair

26. Sebaceous gland

27. Sweat glands

28. Types of nerve endings in skin Free endingMeissner’s corpuscle Merkel’s ending Paccinian corpuscle Krause’s end organ

29. Meissner’s corpuscle

30. Paccinian corpuscle Located deep in dermis Sensation of pressure Characterized by nerve terminal (arrowhead) surrounded by concentric layers of connective tissue cells

31. THE END!