2. GENERAL EMBRYOLOGY
1. Development of embryology
2. Germ cell and fertilization
3. Blastocyst and implantation
4. Formation of the germ layer
5. Differentiation of trilaminar germ and
formation of embryo
6. Fetal membrane and placenta
7. Twins and multiple birth
3. Preembryonic period: 1st week to end of 2nd week
fertilization to formation of bilaminar germ disc
Embryonic period: 3rd week to end of 8th week
formation of embryo
Fetal period: 9th week to birth
growth
Perinatal stage: 26th week to 4 week after birth
7. Germ cell and fertilization
Germ cell
spermatozoon and ovum
1. Spermatozoon
Capacitation：In female reproductive tract, the sperms were
enabled to bind to the zona pellucida receptors.
removal of glycoproteins (decapacitation factor) which cover the
sperms
2. Ovum
secondary oocyte arrested at metaphase in the second meiotic
division
8. Fertilization: The process in which the spermatozoon penetrates
into the ovum to form fertilized ovum.
In the ampulla of oviduct
9. nucleus acrosome
Penetration and
release of acrosomal
enzyme
Cell
membrane
of ovum
Process of fertilization
Sperm bind to sperm receptor ZP-3 induce
Acrosome reaction：release of acrosomal enzyme
11. The second meiotic division
of the secondary oocyte is
rapidly lifted and the second
polar body is released,
leaving a haploid female
nucleus.
Zona reaction: Cortical granules→perivitelline space
→degrade ZP-3, alteration of zona pellucida →barrier
for sperm penetration
16. ① Fusion of the
membrane of
sperm and ovum
② The nucleus
of sperm
penetrate into
ovum
③ Formation of
pronuclei
④ Fusion of
pronuclei
Process of fertilization
Alteration of ovum 24 h
17. 2.Condition of fertilization
① Normal ovum
② Normal sperm
sufficient numbers
③ Certain time
12-24h
④ Free reproductive tract
19. Formation of blastocyst
and implantation
Cleavage and formation of blastocyst
1. Cleavage： early division of fertilized egg
2. Blastomere：daughter cells from cleavage
3. Morula：12 to 16- cell stage, enclosed in the zona pellucida,
like morus
4. Blastocyst：about 100 blastmeres
blastocoele、inner cell mass and trophoblast
polar trophoblast
24. Implantation (imbed)
The process by which the blastocyst settles
into endometrium. 6th day to 11th day
Fundus and body of uterus
zona pellucida disappear at the 5th day
1.Trophoblast：proliferate and differentiate into two layers
①Syncytiotrophoblast：outer layer, fused each other, cell
boundaries disappear
②Cytotrophoblast：inner layer， cell boundaries distinct,
simple cuboidal cells
26. Implantation at 7th day
Endometrium
Polar trophoblast
Inner cell mass
Cytotrophoblast
27. 2.Decidua：
endometrium implantation decidua
decidual response
Decidua basalis：under the implantation site
Decidua capsularis：between the implantation
site and the uterine lumen
Decidua parietalis：remaining endometrium
51. 1、Differentiation of ectoderm
Anterior neuropore closed at 25th
Posterior neuropore closed at 27th
Neural tube
Neural fold
closed at 22nd day, from 4th somite
53. ②Neural crest： blastema of PNS
chromaffin cell, parafollicular cell
some of bone, cartilage and
muscle of head
③Superficial ectoderm: after formation of neural tube
epidermis
54. 2.Differentiation of mesoderm 17th day
①Paraxial mesoderm：somite at 20th day, from the head
Dermotome→ dermis, hypodermis
Myotome → skeletal muscle,
Sclerotome → axial skeleton.
②Intermediate mesoderm：urinary and
reproductive system
③Lateral mesoderm：parietal mesoderm，
viseral mesoderm，
intraembryonic coelomic cavity
58. 3. Differentiation of endoderm
Epithelium of primitive gut →
epithelium of digestive tract, digestive gland,
respiratory tract and lung
Primitive pharynx →5 pairs of pharyngeal pouch
61. Formation of embryonic body (4-8th week)
Disc Columnfolds
the number of somite increase
face development, formation of branchial pouch
breach of buccopharyngeal membrane
5th week: upper and lower limb buds
6th week: hand and foot plates
7th week: formation of face, disappear of somite
8th week: breach of cloacal membrane
20-30th day
80. 5. Umbilical cord：50 cm
(CT, umbilical vein， umbilical artery,
degenerated yolk sac and allantois)
covered with amniotic membrane
Abnormality: ＞80 cm,
＜35 cm
connect fetus with placenta
84. 2.Placental membrane：
Structure between the blood of mother and fetus
①Syncytiotrophoblast；
②Cytotrophoblast and its basal lamina；
③Connective tissue；
④Endothelium and its basal lamina
protection
86. 3.Function：
① Substance exchange
O2, nutriment, CO2, waste
② Hormone
Human chorionic gonadotropin, HCG;
Human placental lactogen, HPL;
Human placental progesterone, HPP,
Human placental estrogen, HPE
