Skin Jun Zhou School of Medicine, Zhejiang University

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

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

Structure of skin Epidermis ( 表皮 ) Dermis ( 真皮 )

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

Keratinised cell  from basal to surface  five layers

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

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

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

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: / nm membrane-coated /contain phospholipid and steroid  intercellular bridges- Desmosome

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）

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

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

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

Melanocytes 黑素細胞 Melanocytes Dermis Basal cells contain brown pigment

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

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

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

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

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

Hypodermis （皮下组织） LCT and fat tissue

skin appendages

Hair

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

Hair follicle Dermis Sebaceous gland Hair follicle Hair

Sebaceous gland

Sweat glands

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

Meissner’s corpuscle

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

THE END!