1. 组织胚胎学课件
中国医科大学
基础医学院
组胚—英文教学组

2. HUMAN EMBRYOLOGY Department of Histology and Embryology
China Medical University

3. Fetal Membranes and Placenta
Chapter 5
Fetal Membranes and Placenta

4. Fetal membranes and placenta are auxiliary structures of the embryo and fetus.
They have functions of protection, nutrition, respiration and excretion. Some of them can produce hormone to maintain the pregnancy.
After the infant is born, fetal membranes and placenta will separate from uterus and be extruded out of body.

5. Fetal membranes Chorion Amnion Yolk sac
Allantois (allantoic diverticulum)
Umbilical cord

6. 1. chorion:
trophoblast
extra-embryonic mesoderm

8. extra-embryonic mesoderm
syncytiotrophoblast
cytotrophoblast
capillary
intervillous space
blood vessel
decidua
Primary villi: a central core of cytotrophoblast covered by a layer of syncytiotrophoblast. Adoining villi are separated by an intervillous space.

10. An inner layer extra-embryonic mesoderm
cytotrophoblast
syncytiotrophoblast
intervillous space
extra-embryonic mesoderm
capillary
blood vessel
decidua
secondary villi :
An inner layer extra-embryonic mesoderm
An intermediate layer cytotrophoblast
An outer layer syncytiotrophoblast

11. cytotrophoblast
syncytiotrophoblast
intervillous space
extra-embryonic mesoderm
capillary
blood vessel
decidua
tertiary villi: are like secondary villi except that extra-embryonic mesoderm differentiate into capillaries and CT.

12. formation of cytotrophoblastic shell

13. formation of cytotrophoblastic shell

14. formation of cytotrophoblastic shell

17. 2. Yolk sac:
---blood island: primitive blood cell- derived from extra-embryonic mesoderm on the wall of yolk sac
---primordial germ cell: derived from endoderm of yolk sac

18. 3.Amnion:
---amniotic membrane: amniotic epi. + extra-embryonic mesoderm
---amniotic fluid:
/secreted by amniotic epi.
/slight basic fluid: ml
-polyhydramnios: >2000 ml, abnormal digestive system or CNS
-oligohydramnios: <500 ml, abnormal urinary system

22. /function:
-intra-environment
-protecting
-preventing from adherence
-wash germ tract

23. 4. Allantois (allantoic diverticulum)
---allantoic A: paired, →umbilical A
---allantoic V: paired
right: degenerate
left: umbilical V

24. 5. Umbilical cord
---cylindrical structure
---surface: amniotic membrane
---cord: mucous CT, umbilical A,V,
yolk sac and allantois
cm long, cm in D
---> 80 cm, or < 35 cm

25. Placenta
---the structure by which exchange of material between fetus and mother takes place.
---it consists of chorionic plate and basal plate.
---size: round, disc-shaped, cm in D, 2.5 cm thickness, 500g in weight

26. fetal surface: smooth, covered by amniotic membrane
mother surface: rough, cotyledons

27. ---structure:
1. chorionic plate
chorion and chorion space
-chorion: 60 chorion stalks→branches
-chorion space: space between chorion,
filled with mother blood

28. 2. basal plate:
cytotrophoblastic shell + decidua basalis
placental septa: separate the chorion into
cotyledon

29. ---blood circulation of placenta
fetus: umbilical A →cap. of chorion →umbilical V
mother: spiral A → chorion space →
uterus V

30. the structures between fetal and maternal blood ---components:
* placental barrier:
the structures between fetal and maternal blood
---components:
a. the endothelium fetal blood vessels, and its
basement membrane.
b. surrounding mesoderm (connective tissue).
c. cytotrophoblast, and its basement membrane.
d. syncytiotrophoblast.

31. ---function:
a. the exchange of material between
the maternal and fetal blood streams
b. defense barrier
c. the production of hormones:
/human chorionic gonadotropin, HCG:
-begin: end of 2nd week
-highest level: 9th –11th week
-lowest level: 20th week, until birth

32. /human placental lactogen, HPL
-similar to HGH
-highest level: 36th –37th week
/human placental progesterone, HPP
and human placental estrogen, HPE
-begin: 4th month
/other hormones: human chorionic
thyrotropin, HCT; human chorionic
adrenocorticotrophic hormne, HCATH;
prostaglandin

33. DIZYGOTIC TWINS
Approximately two-thirds of twins are dizygotic, or fraternal, and their incidence
of 7 to 11 per 1000 births increases with maternal age. They result from
simultaneous shedding of two oocytes and fertilization by different spermatozoa.

34. MONOZYGOTIC TWINS
The second type of twins, which develops from a single fertilized ovum, is monozygotic, or identical twins. The rate for monozygotic twins is 3 to 4 per They result from splitting of the zygote at various stages of development.
The second type of twins, which develops from a single fertilized ovum, is monozygotic, or identical, twins. The rate for monozygotic twins is 3 to 4 per They result from splitting of the zygote at various stages of development.

36. Fetal Membranes and Placenta
Chapter 5
Fetal Membranes and Placenta
Questions
What’re the fetal membranes? How many types of fetal
membranes are there? Describe the development and
evolution of each fetal membrane.
2. Describe the formation, structure and function of the
placenta.
3. Describe the classification of twins.