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

HUMAN EMBRYOLOGY Department of Histology and Embryology China Medical University

Fetal Membranes and Placenta Chapter 5 Fetal Membranes and Placenta

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.

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

1. chorion: trophoblast extra-embryonic mesoderm

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.

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

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.

formation of cytotrophoblastic shell

formation of cytotrophoblastic shell

formation of cytotrophoblastic shell

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

3.Amnion: ---amniotic membrane: amniotic epi. + extra-embryonic mesoderm ---amniotic fluid: /secreted by amniotic epi. /slight basic fluid: 1000-1500ml -polyhydramnios: >2000 ml, abnormal digestive system or CNS -oligohydramnios: <500 ml, abnormal urinary system

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

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

5. Umbilical cord ---cylindrical structure ---surface: amniotic membrane ---cord: mucous CT, umbilical A,V, yolk sac and allantois ---40-60 cm long, 1.5-2.0 cm in D ---> 80 cm, or < 35 cm

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, 15-20 cm in D, 2.5 cm thickness, 500g in weight

fetal surface: smooth, covered by amniotic membrane mother surface: rough, 15-30 cotyledons

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

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

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

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.

---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

/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

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.

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 1000. 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 1000. They result from splitting of the zygote at various stages of development.

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.