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Fetal Membranes, Placenta and Twinning
Jun Zhou(周俊)
School of Medicine, ZheJiang University
20140106
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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
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Chorion•Formed by
trophoblast +extraembryonic mesoderm
•Chorion frondosum
(bushy chorion)- embryonic pole
•Chorion laeve
(smooth chorion)- abembryonic pole
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Development of villiWeek 2 to week 3 Primary villi: cytotrophoblast+syncytiotrophoblast
Secondary villi: extraembryonic mesoderm enter the
primary villi
Tertiary villi: extraembryonic mesoderm =>CT+BV
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Function of Chorion1) Exchange of metabolite:
portion of placenta (Chorion frondosum)
2) Hormone production:
human chorionic gonadotropin (HCG)
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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
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Amnion - Fluid Functions
Mechanically cushion Protect from fetus adhesion Movement Maintain Temp
Abnormalities1) too much (polyhydramnios) >2000 ml Abnormal digestive system or CNS - esophageal atresia - anencephaly2) too little (oligohydramnios) <500 ml Abnormal urinary system - poor development of kidney - urethra atresia
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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
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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
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Placenta - Overview Functions as:
Lungs, GI tract, Liver, Kidneys, Endocrine
Placenta proper: Chorion frondosum (fetus)+ Decidua basalis (mother)
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Anatomy of the Placenta
Fetal – Chorion Chorion Frondosum Chorion Laeva
Maternal – Decidua Decidua Basalis Decidua Capsularis Decidua Parietalis
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Anatomy of the Placenta
At birth 500 g 15-25 cm Diameter 3 cm thick Anchoring villi Decidual septa
15-20 Cotyledons
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Placental-Fetal Circulation Fetus:
umbilical A carries O2/nutrient depleted blood to cap. of chorion , exchange with maternal blood of the intervillous spaceumbilical V
Mother:
spiral A intervillous space uterine V
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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
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Placental Function1.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
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Twins
Two types: One zygote (monozygotic) Two (or more) zygotes
(dizygotic)2 (or more) oocytesNon Identical
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Twins - Monozygotic
Zygote split 2-4 cell
2 amn, 2 chorion
Blastocyst 2 amn, 1 chorion
(most common)
Bilaminar germ disc1 amn, 1 chorion
(rarely happen)
Incomplete splitting Conjoined twins
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Conjoined Twins
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OBJECTIVES
1. The components of fetal membrane and their functions.
2. Structure and function of placenta
3. Composition of Placenta barrier