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Fetal Membranes, Placenta and Twinning

Fetal Membranes, Placenta and Twinning. Jun Zhou （周俊） School of Medicine, ZheJiang University 20140106. Fetal membrane — overview. Originate from blastocyst, don’t participate in the formation of embryo Including: 1) Chorion 2) Amnion 3) Yolk sac 4) Allantois 5)Umbilical cord. Chorion.

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Fetal Membranes, Placenta and Twinning

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  1. Fetal Membranes, Placenta and Twinning Jun Zhou（周俊） School of Medicine, ZheJiang University 20140106

  2. Fetal membrane — overview • Originate from blastocyst, don’t participate in the formation of embryo • Including: • 1) Chorion • 2) Amnion • 3) Yolk sac • 4) Allantois • 5)Umbilical cord

  3. Chorion • Formed by • trophoblast +extraembryonic mesoderm • Chorion frondosum • (bushy chorion)- embryonic pole • Chorion laeve • (smooth chorion)- abembryonic pole

  4. Development of villi Week 2 to week 3 • Primary villi: cytotrophoblast+syncytiotrophoblast • Secondary villi: extraembryonic mesoderm enter the primary villi • Tertiary villi: extraembryonic mesoderm =>CT+BV

  5. Function of Chorion • Exchange of metabolite: • portion of placenta (Chorion frondosum) • 2) Hormone production: • human chorionic gonadotropin (HCG)

  6. Amnion • Amniotic membrane: amniotic epi.+ extraembryonic mesoderm • Amniotic fluid: • Produce:1)amniotic cells • 2) infusion of fluid from maternal blood • 3) urine output from the fetus • 4) pulmonary secretions • Output: 1) absorbed by amniotic cells • 2) fetus swallow • 30 ml--- 10 weeks • 450 ml--- 20 weeks • 800-1000 ml --- 37 weeks---circulate

  7. Amnion - Fluid • Functions • Mechanically cushion • Protect from fetus adhesion • Movement • Maintain Temp • Abnormalities 1) too much (polyhydramnios) >2000 ml Abnormal digestive system or CNS - esophageal atresia - anencephaly 2) too little (oligohydramnios) <500 ml Abnormal urinary system - poor development of kidney - urethra atresia

  8. Yolk sac and Allantois • Yolk sac • Primitive Gut • 3rd week, Germ Cells • 3rd to 6th week, Blood island • Allantois • Caudal extension of hindgut • Allantoic A pairs • Allantoic V pairs Umbilical vessels 2A+1V

  9. Umbilical Cord • Folding – a purse string closure • Amnion membrane covered • Cord: mucous CT, 3 vessels,yolk sac ,allantois • At birth, 50-60 cm, 2cm diameter • Long – knots • Short – placenta detachment

  10. Placenta - Overview • Functions as: • Lungs, GI tract, Liver, Kidneys, Endocrine • Placenta proper: Chorion frondosum (fetus)+ Decidua basalis (mother)

  11. Anatomy of the Placenta • Fetal – Chorion • Chorion Frondosum • Chorion Laeva • Maternal – Decidua • Decidua Basalis • Decidua Capsularis • Decidua Parietalis

  12. Anatomy of the Placenta • At birth 500 g • 15-25 cm Diameter • 3 cm thick • Anchoring villi • Decidual septa  15-20 Cotyledons

  13. Placental-FetalCirculation • Fetus: umbilical A carries O2/nutrient depleted blood to cap. of chorion , exchange with maternal blood of the intervillous spaceumbilical V • Mother: spiral A intervillous space uterine V

  14. Placental Barrier --the structure between fetal and maternal blood --components: 1)endothelium of chorion capillary 2) CT in the core of the villus 3) trophoblast epithelium

  15. Placental Function 1.Exchange of Metabolites: nutrients antibody, waste 2.Defense barrier 3.hormone production • human chorionic gonadotropin (HCG) Begin: end of 2nd week Highest: 2nd month • Estrogen and progesterone • Placental lactogen

  16. Twins Two types: • One zygote (monozygotic) • Two (or more) zygotes (dizygotic) • 2 (or more) oocytes • Non Identical

  17. Twins - Monozygotic • Zygote split • 2-4 cell • 2 amn, 2 chorion • Blastocyst • 2 amn, 1 chorion (most common) • Bilaminar germ disc • 1 amn, 1 chorion (rarely happen) • Incomplete splitting • Conjoined twins

  18. Conjoined Twins

  19. OBJECTIVES • The components of fetal membrane and their functions. • Structure and function of placenta • Composition of Placenta barrier

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