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

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

3. Fetal membrane （胎膜）
Originate from blastocyst（胚泡）, don’t participate in the formation of embryo
Including:
1) Chorion（绒毛膜）
2) Amnion（羊膜）
3) Yolk sac（卵黄囊）
4) Allantois（尿囊）
5)Umbilical cord（脐带）

4. Chorion（绒毛膜） Formed by trophoblast +extraembryonic mesoderm
Chorion frondosum（丛密绒毛膜）-embryonic pole
Chorion laeve（平滑绒毛膜）-abembryonic pole

5. Chorion Primary villi (2w): cytotrophoblast+syncytiotrophoblast
Secondary villi (3w):extraembryonic mesoderm enter the
primary villi
Tertiary villi (end of 3w): extraembryonic mesoderm
=>CT+BV

6. Function of Chorion Exchange of metabolite: 2) Hormone production:
portion of placenta (Chorion frondosum)
2) Hormone production:
human chorionic gonadotropin绒毛膜促性腺激素 (HCG)

7. Amnion（羊膜） Amniotic membrane: amniotic epi.+ extraembryonic mesoderm
Amniotic fluid:
Produce:1)amniotic cells
2) urine output from the fetus
Output: 1) absorbed by amniotic cells
2) fetus swallow
1-1.5 liter – circulate

8. Amnion - Fluid Functions Mechanically cushion
Protect from fetus adhesion
Movement
Maintain Temp

9. Abnormalities 1) too much (polyhydramnios) >1500 ml
Abnormal digestive system or CNS
- esophageal atresia(食管闭锁）
- anencephaly（无脑儿）
2) too little (oligohydramnios)
<500 ml
Abnormal urinary system
- poor development of kidney（肾脏发育不全）
- urethra atresia（尿道闭锁）

10. Yolk sac and Allantois Yolk sac（卵黄囊） Allantois（尿囊） Primitive Gut
3rd week, Germ Cells
3rd to 6th week,
Blood island
Allantois（尿囊）
Caudal extension of hindgut
Allantoic A pairs
Allantoic V pairs
Umbilical vessels 2A+1V

11. Umbilical Cord（脐带） Folding – a purse string closure
Amnion membrane covered
Cord: mucous CT, 3 vessels,yolk sac ,allantois
50-60 cm, 2cm diameter
Long (>80cm)– knots
Short (<35cm)– abruption

12. Placenta（胎盘） - Overview
Functions as:
Lungs, GI tract, Liver, Kidneys, Endocrine
Placenta proper:
Chorion frondosum（丛密绒毛膜）+ Decidua basalis（底蜕膜）

13. Anatomy of the Placenta
Fetal – Chorion
Chorion Frondosum
Chorion Laeva
Maternal – Decidua
Decidua Basalis（底）
Decidua Capsularis（包）
Decidua Parietalis（壁）

14. Anatomy of the Placenta
At birth 500 g
15-25 cm Diameter
3 cm thick
Anchoring villi（固定绒毛）
Placental septa  Cotelydons（胎盘小叶）

15. 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

16. Placental Barrier（胎盘屏障）
--the structure between fetal and maternal blood
--components:
1)Endothelium /basement membrane of chorion capillary
2) CT in the core of the villus
3) trophoblast epithelium /basement membrane

17. Placental Function
1.Exchange of Metabolites: nutrients antibody, waste
2.Defense barrier
3.hormone production
human chorionic gonadotropin (HCG)
（绒毛膜促性腺激素）
Begin: end of 2nd week
Highest: 2nd month
Estrogen and progesterone（雌激素和孕激素）
Placental lactogen（胎盘催乳素）

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

19. Twins - Monozygotic Zygote split 2-4 cell Blastocyst
2 amn, 2 chorion
Blastocyst
2 amn, 1 chorion
Bilaminar germ disc
1 amn, 1 chorion
Incomplete splitting
Conjoined twins

20. Conjoined Twins