GENERAL EMBRYOLOGY1. Development of embryology2. Germ cell and fertilization3. Blastocyst and implantation4. Formation of the germ layer5. Differentiation of trilaminar germ and

formation of embryo6. Fetal membrane and placenta7. Twins and multiple birth

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

Human ？

Plant

Animal

Development of embryology

Semen+menstration

Harvey, 1651: All life from oocyte

Malpighi, 1675: A micro-chicken in an egg

Leewenhoek, 1677 : A micro-human in a sperm

Aristotle, B.C 384-322

Haeckel, 1868 Biogenetic law

Spemann, 1869-1941

Experimental embryology

Wilmut,1997 Dolly

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

Fertilization: The process in which the spermatozoon penetrates into the ovum to form fertilized ovum. In the ampulla of oviduct

nucleus acrosome

Penetration and release of acrosomal enzyme

Cell membrane of ovum

Process of fertilizationSperm bind to sperm receptor ZP-3 induceAcrosome reaction ： release of acrosomal enzyme

ovum

fertilized ovum

sperm

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

Contac of sperm and ovum

Sperm penetrate into the ovum

Formation of female and male pronucleus

Fusion of pronuclei

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

2.Condition of fertilization ① Normal ovum

② Normal sperm

sufficient numbers

③ Certain time

12-24h

④ Free reproductive tract

3.Significance of fertilization ① A new life

② Diploid

inheritance and aberrance

③ Sex determination

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

Phase of cleavage

Fertilized egg

2-cell stage

18~36h

4-cell stage

36~48h

8-cell stage

48~60h

Morula

12 to 16-cell stage

The third day

Appearance and inner structure of blastocyst

Appearance Inner structure

Movement of fertilized egg in the oviduct

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 day1.Trophoblast ： proliferate and differentiate into two layers①Syncytiotrophoblast ： outer layer, fused each other, cell

boundaries disappear②Cytotrophoblast ： inner layer ， cell boundaries distinct,

simple cuboidal cells

Movement and implantation of fertilized egg

Implantation at 7th day

Endometrium

Polar trophoblast

Inner cell mass

Cytotrophoblast

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

Decidua

Formation of germ layer

Bilaminar germ disc

1.Bilaminar germ disk ： Inner cell mass→2 layers of cell in disc (7th day)

Epiblast: columnar cells adjacent to trophoblast

Hypoblast: cuboidal cells adjacent to blastocoele

Bilaminar germ disc

Epiblast

Hypoblast

Columnar cells

Cuboidal cells

Epiblast

Hypoblast

2. Amnion ： 8th day

epiblast → amnioblast → aminiotic membrane → amniotic cavity → amniotic fluid

3.Primary yolk sac ： 9th day

hypoblast →extraembyronic endoderm →primary yolk sac

Bilaminar germ disc at 9th day

Hypoblast

Epiblast

Amniotic cavity

Syncytio-trophoblast

Primary yolk sac

Bilaminar germ disc

Decidua

Syncytiotrophoblast

Epiblast

HypoblastPrimary yolk sac

Amniotic cavity

Cytotrophoblast

4. Extraembryonic mesoderm: 10th-11th day

5. Extraembryonic cavity: 12th-13th day Extraembryonic mesoderm: visceral layer

parietal layer

6. Secondary yolk sac: 13th day

7. Body stalk: 14th day

Embryo at 10th dayPrimary yolk sac

Extraembryonic mesoderm

Germ disc

Amnion

Bilaminar germ disc

Decidua

Amniotic cavityEpiblast

Hypoblast

Extraembryonic mesoderm

Primaryyolk sac

Cytotrophoblast

Syncytiotrophoblast

Embryo at 13th day

Extraembryonic cavity

Primary yolk sac

Secondary yolk sac

Body stalk

Bilaminar germ disc

Body stalk

Secondary yolk sac

Extraembryonic cavity

Primary stem villus

Extraembryonic mesodermVisceral layer

Extraembryonic mesoderm

Parietal layer

Trilaminar germ disc

primitive streak, primitive groove 3rd week

primitive node, primitive pit 3rd week

1. Endoderm: primitive groove →hypoblast → endoderm

2. Mesoderm ： primitive groove →between epiblast and hypoblat →mesoderm

3. Ectoderm ： epiblast →ectoderm

Formation of trilaminar germ

Primitive streak

Epiblast

Hypoblast

Epiblast

Hypoblast

Primitive streak

Determine the

direction of the

embryo

notochord

Primitive node

Primitive

pit

Primitivegroove

Primitivestreak

Significance of

primitive streak

Hypoblast

Epiblast

Primitive

streak

Endoderm

Formation of endoderm

Epiblast

Endoderm

Formation of mesoderm

Mesoderm

Ectoderm

Endoderm

Mesoderm

Trilaminar germ disc

Epiblastproliferation

Primitive pit

Headprocess

Notochordal tube

Neurenteric canal

Notochord

Significance of notochord ?

No mesoderm

Buccopharyngeal membrane

Cloacal membrane

Differentiation of trilaminar germ and formation of embryo

Differentiation of trilaminar germ1.Differentiation of ectoderm

①Neural tube ： blastema of CNS

neural plate (18th-19th day) Neuro-epithelium (neural ectoderm): pseudostratified columnar

→neural groove , neural fold

→ neural tube (closed at 22nd day)

Neural groove Paraxial mesoderm Intermediate mesoderm

Neural groove

Paraxial mesoderm intermediate mesoderm

Neural groove

Neural crest

Notocord

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

Unclosed Anterior neuropore Unclosed Posterior neuropore

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

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

Somite

Parietal mesoderm Intraembryonic

coelomic cavit

Visceral mesoderm

Differentiation of lateral mesoderm

Dermatome

Sclerotome

Extraembryonic coelomic cavity

Intraembryonic coelomic cavity

Differentiation of lateral mesoderm

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

Formation of primitive gut

A B

Parietal mesoderm

Intraembryonic coelomic cavity

Visceral mesoderm

Formation of embryonic body (4-8th week)

Disc Column folds

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

At the end of 8th week—

a small human

Fetal membrane and placenta

Fetal membrane

Chorion Amnion Yolk sac Allantois Umbilical cord

Amnion

Yolk sac

Umbilical cord

Placenta

1.Chorion ： Secondary stem villus +chorinic plate

Primary stem villus ： 2nd week

Outer syncytiotrophoblast+ Inner cytotrophoblast

Chorinic plate : extraembryonic mesoderm + trophoblast

Secondary stem villus ： 3rd week

Outer syncytiotrophoblast+

Intermedial extraembryonic mesoderm+

Inner cytotrophoblast

Tertiary stem villus ： end of 3rd week, Blood vessels

Anchoring villus, Free villus cytotrophoblastic cell column → cytotrophoblastic shell

Primary stem villus ： at 2nd week ， cytotrophoblast

Secondary stem villus ： at 3rd week ， extraembryonic mesoderm Tertiary stem villus ： at the end of 3rd week ， blood

vessels

Anchoring villus

Free villus

Cytotrophoblastic shell

Cytotrophoblastic column

Stem villus

Evolvement of chorion

Chorion laeve Chorion frondosum

6th weeks

Chorion laeve ： adjacent to decidua capsularisChorion frondosum ： adjacent to decidua basalis

Abnormility of chorion ：

Hydatidiform

Hydatidiform

• Chorion carcinoma

• Chorion carcinoma

Picture

Hydatidiform

Hydatidiform

Hydatidiform

Chorion carcinoma

Chorion carcinoma

Chorion carcinoma

2. Yolk sac ： 5th-6th week, atresia

Abnormality: ① Meckel’s diverticulum

② Umbilical fistula 　

① Primitive blood cells

② Primordial germ cells

3. Amnion ： amniotic membrane: 0.2-0.5mm

amniotic epithelium + extraembryonic mesoderm

amniotic fluid: 500-1000ml

abnormality: ＜ 500 ml, oligohydramnios

＞ 2000 ml, polyhydramnios

protection

4. Allantois ： degeneration Abnormality: Urachal fistula

2 pairs of blood vessel→ 1 umbilical vein 1 pair of umbilical artery

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

Fetal membrane

Placenta1.Placenta: Chorion frondosum + Decidua basalis

disk: 15-20cm Sandwich: chorinic plate (fetus) villi basal plate (mother) basal plate: decidua + cytotrophoblastic shell

placental septa → cotyledon (incomplete)

Umbilical arteryUmbilical vein

Spiral arteryUterus vein

Decidua bsalisPlacenta septa

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

胎儿血

Syncytiotrophoblast

Cytotrophoblast

Basal lamina

Connective tissue

Basal lamina

Endothelium

Nutriment

Metabolic product

Fetal membrane

Blood of mother

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

FunctionFunction

① Substance exchange

　　　

① Substance exchange

　　　

Placenta

Capillary of fetus Blood of mother

Ｏ 2

Nutriment

water 、 salt 、 others water 、 salt 、 others

ＣＯ 2

Metabolic waste

Placenta membrane

FunctionFunction

② Barrier

　　　

② Barrier

　　　

Placenta

Capillary of fetus Blood of mothers

Placenta barrier

No way！

Most of microorganism

FunctionFunction

② Barrier

　　　

② Barrier

　　　

Placenta

Capillary of fetus Blood of mother

Most of drugs

Placenta barrier

Most of microorganism

Some of microorganism

FunctionFunction

③ Endocrine ③ Endocrine

Placenta

Hormone Function Appearance Fastigium

HCGCorpus luteum

Pregnancy3rd week 8th week

HCSMammary

gland2nd month 8th month

HPE Corpus luteum 4th month 8th month

HPP Corpus luteum 4th month 8th month

Twins and multiple birth

1.Twins monozygotic twins

dizygotic twins

2.Multiple birth monozygotic multiple birth

polyzygotic multiple birth

mixed multiple birth

Dizygotic twins

Blastocyst Blastocyst

2 Amnion 2 Amnion2 Chorion 2 Chorion2 Placenta 2 Placenta

Monozygotic twins

separation of blastomere, of ICM, of primitive streak

Blastocyst 2 ICM 2 primitive streak

2 Amnion 2 Amnion 1 Amnion

2 Chorion 1 Chorion 1 Chorion

2 Placenta 1 Placenta 1 Placenta