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Understanding Fetal Membranes, Placenta & Birth Defects

Discover the components and functions of fetal membranes, the structure of the placenta, periods of vulnerability, and the composition of the placental barrier. Gain insights into birth defects causes and the impact of genetic and environmental factors.

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Understanding Fetal Membranes, Placenta & Birth Defects

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  1. Fetal Membranes, Placenta andBirth defects Jun Zhou（周俊） School of Medicine, ZheJiang University 20160113

  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) • ( Early indication of pregnancy)

  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. Birth defect, congenital malformation and congenital anomaly • Are synonymous terms used to describe structural, behavioral, functional and metabolic disorders present at birth

  17. Causes of Birth Defects • Genetic/Chromosomal - 15-20% • Environmental (teratogens) - 10-15% • Combined - 20-25% • Multiple Gestations - 1% • Unknown - 40-50%

  18. Genetic Causes • Molecules that regulate development • Enzymes • Structural genes • Localized to a Chromosome – gene unknown

  19. Environmental factors (Teratogens) • Infectious agents-virus • Physical agents X-rays, Hyperthemia, etc • Chemicals agents alcohol, Cocaine, etc • Hormones • Maternal diabetes

  20. Periods of Vulnerability • Preembryonic period Pregerm (0-2 wks) • Usually Death • Embryonic period Organogenesis (3-8 wks) • Abnormalities of Form (malformations) • Fetal period Growth/Maturation (9 wks – birth) • Growth Retardation • Mental dysfunction • Fetus vulnerable • Rapid cell proliferation • Cell migration • Cell differentiation

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

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