Download Chorion

Fetal Membranes, Placenta and
Twinning
Jun Zhou（周俊）
School of Medicine, ZheJiang University
20130114
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
•Formed by
trophoblast +extraembryonic mesoderm
•Chorion frondosum
(bushy chorion)- embryonic pole
•Chorion laeve
(smooth chorion)- abembryonic pole
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
Function of Chorion
1) Exchange of metabolite:
portion of placenta (Chorion frondosum)
2) Hormone production:
human chorionic gonadotropin (HCG)
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
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
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
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
Placenta - Overview
 Functions as:
 Lungs, GI tract, Liver, Kidneys, Endocrine
 Placenta proper:
Chorion frondosum (fetus)+ Decidua basalis (mother)
Anatomy of the Placenta
 Fetal – Chorion
 Chorion Frondosum
 Chorion Laeva
 Maternal – Decidua
 Decidua Basalis
 Decidua Capsularis
 Decidua Parietalis
Anatomy of the Placenta
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At birth 500 g
15-25 cm Diameter
3 cm thick
Anchoring villi
Decidual septa 
15-20 Cotyledons
Placental-Fetal Circulation
 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
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
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
Twins
Two types:
 One zygote (monozygotic)
 Two (or more) zygotes
(dizygotic)
 2 (or more) oocytes
 Non Identical
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
Conjoined Twins
OBJECTIVES
1. The components of fetal membrane and their
functions.
2. Structure and function of placenta
3. Composition of Placenta barrier