Integumentary system. Min-Chuan Huang 台大醫學院解剖學暨細胞生物學研究所黃敏銓

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1 Integumentary system Min-Chuan Huang 台大醫學院解剖學暨細胞生物學研究所黃敏銓 1

2 Integumentary system Skin: Epidermis Dermis Skin appendages Sebaceous glands Sweat glands Mammary glands Hair Arrector pili muscles Nails Teeth 2

Development of skin: overview 4 weeks Embryonic skin: begins from embryo of 4-5 weeks Epidermis: surface ectoderm Dermis: mesoderm Mutual inductive mechanism for

3 Development of skin: overview 4 weeks Embryonic skin: begins from embryo of 4-5 weeks Epidermis: surface ectoderm Dermis: mesoderm Mutual inductive mechanism for ectodermal/mesenchymal interactions (epidermal / dermal interactions) WNT, fibroblast growth factor (FGF), transforming growth factor-β (TGF-β), sonic hedgehog (SHH) 3

4 Development of epidermis: early stage 4 weeks 7 weeks 4 weeks: primordial skin from surface ectoderm 7 weeks: Periderm: single layer of squamous epithelium - Continue keratinization, desquamation - Exfoliated cells form part of vernix caseosa Basal layer: proliferation 4

5 Development of Epidermis at 11 weeks Stratum germinativum Epidermal ridges: begin at 10 weeks, permanently established at 19 th week; genetically determined (fingerprint), Dermatoglyphics 皮紋學 Intermediate layer: from stratum germinativum Migration of neural crest cells to developing dermis (melanoblasts), later melanocytes (as early as days) in stratum germinativum 11 weeks 5

6 Development of epidermis: 21 st week forward (periderm disappears) ichthyosis: severe keratinization Newborn Stratum corneum: originally periderm Appearance of stratum lucidum, granulosum, spinosum Melanocytes fail to produce melanin: 1. Generalized albinism 2. Localized albinism (piebaldism) 6

7 Development of Dermis Mesenchyme from mesoderm: (major) somatic layer of lateral mesoderm & (minor) dermatomes of somites By 11 weeks: mesenchymal cells produce collagenous & elastic connective tissues fibers Dermal ridge: with capillary loops & sensory nerve endings Capillary-like vessels: derived from mesenchyme, begin at the end of 5th week 11 weeks 7

8 Week 16 Week 20 Development of sebaceous glands Glandular buds from sides of developing epidermal root sheaths of hair follicles, branch to form primordia of alveoli & ducts Central cells of alveoli: break down, release into hair follicle, mix with desquamated peridermal cells (vernix caseosa) Sebaceous glands independent of hair follicles: in external genital organs 8

9 Development of eccrine sweat glands Epidermal downgrowth into dermis by elongation, and coiling End: primordium of secretory part; (1) myoepithelial cells, (2) secretory cells Epithelial attachment: primordium of duct, central cells degenerate Begin to function after birth 20 weeks 9

10 Development of apocrine sweat glands Axilla, pubic, perineal regions, areolae of the nipples Downgrowths of stratum germinativum giving rise to hair follicles Open into the upper part of hair follicles superficial to the openings of sebaceous glands Secrete during puberty Pheromone 10

11 Week 9-12 Development of hair (1/2) Hair follicle: stratum germinativum into dermis Hair bud Hair bulb (primordium of hair root) Germinal matrix, invaginated by mesenchymal hair papilla Hair shaft: keratinized portion 11

12 Development of hair (2/2) Week 12 Week 20 Epidermal root sheath: from peripheral cells of hair follicles Dermal root sheath: from mesenchymal cells Lanugo: the first hair, end of 12th week, replaced during perinatal period Melanocyte in hair bulb from migrating melanoblast Arrector pili muscles from mesenchyme, goose bumps 12

13 Hypertrichosis 13

14 Hypertrichosis Nature Alopecia 14

15 Folliculogenesis Hair cycling 15

16 Hair follicle stem cells in bulge region 16 Stem Cells 2005;23:

17 Hair follicle stem cells Hair follicles Schwann cells Neurons Glial cells Keratinocytes/sebaceous glands Smooth muscle cells Blood vessels Adipocytes Hematopoietic cells 17

18 We need tissue regeneration instead of scar formation Nature : Myocardial infarction Spinal cord injury Liver cirrhosis Lung fibrosis

19 Development of mammary glands Mammary ridges: 4 th week; thickened strips of ectoderm from axillary to inguinal regions Mammary buds: downgrowth of epidermis at 6 th week 19

20 Supernumerary nipples Supernumerary breasts 1% of the female 5.6% 20

21 Development of mammary glands Mammary buds: primary bud secondary buds lactiferous ducts/branches: canalization by placental sex hormones Mammary pits: depressed epidermis nipples rise by proliferation of connective tissues (areola) 21 Flat or inverted nipples (10-20%)

Two main classes: Epithelial Connective (synovial) Epithelial. Cutaneous Mucous Serous

Two main classes: Epithelial Connective (synovial) Epithelial Cutaneous Mucous Serous Epithelial Membranes = sheet of epithelia + connective tissue base 1. Cutaneous membrane: outer skin layer (stratified