Download 人体组织学与胚胎学

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
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
syncytiotrophoblast
cytotrophoblast
extra-embryonic mesoderm
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.
syncytiotrophoblast
cytotrophoblast
extra-embryonic mesoderm
capillary
intervillous space
blood vessel
decidua
secondary villi :
An inner layer extra-embryonic mesoderm
An intermediate layer
cytotrophoblast
An outer layer
syncytiotrophoblast
syncytiotrophoblast
cytotrophoblast
extra-embryonic mesoderm
capillary
intervillous space
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 cellderived 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
* 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 twothirds 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.
Chapter 5
Fetal Membranes and Placenta
Question
s
1. 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.