GENERAL EMBRYOLOGY 1 Development of embryology 2 Germ

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

Preembryonic period: 1 st week to end of 2 nd week fertilization to formation of bilaminar germ disc Embryonic period: 3 rd week to end of 8 th week formation of embryo Fetal period: 9 th week to birth growth Perinatal stage: 26 th week to 4 week after birth

Animal Plant Human ？

Development of embryology Aristotle, B. C 384 -322 Semen+menstration Harvey, 1651: All life from oocyte Malpighi, 1675: A micro-chicken in an egg Leewenhoek, 1677 : A micro-human in a sperm

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

Process of fertilization Sperm bind to sperm receptor ZP-3 induce Acrosome reaction：release of acrosomal enzyme Penetration and release of acrosomal nucleus acrosome enzyme Cell membrane of ovum

ovum fertilized ovum sperm

Zona reaction: Cortical granules→perivitelline space →degrade ZP-3, alteration of zona pellucida →barrier for sperm penetration § The second meiotic division of the secondary oocyte is rapidly lifted and the second polar body is released, leaving a haploid female nucleus.

Contac of sperm and ovum

Sperm penetrate into the ovum

Formation of female and male pronucleus

Fusion of pronuclei

Process of fertilization ① Fusion of the membrane of sperm and ovum ② The nucleus of sperm penetrate into ovum ③ Formation of pronuclei Alteration of ovum ④ Fusion of pronuclei 24 h

2. Condition of fertilization ① Normal ovum ② Normal sperm sufficient numbers ③ Certain time 12 -24 h 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 18~36 h 4 -cell stage 36~48 h 8 -cell stage 48~60 h

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. 6 th day to 11 th day Fundus and body of uterus zona pellucida disappear at the 5 th 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

Movement and implantation of fertilized egg

Implantation at 7 th day Cytotrophoblast Inner cell mass Polar trophoblast Endometrium

2. Decidua： endometrium implantation decidual response Ø Decidua basalis：under the implantation site Ø Decidua capsularis：between the implantation site and the uterine lumen Ø 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 (7 th day) Epiblast: columnar cells adjacent to trophoblast Hypoblast: cuboidal cells adjacent to blastocoele

Epiblast Columnar cells Hypoblast Cuboidal cells Bilaminar germ disc Epiblast Hypoblast

2. Amnion： 8 th day epiblast → amnioblast → aminiotic membrane → amniotic cavity → amniotic fluid 3. Primary yolk sac： 9 th day hypoblast →extraembyronic endoderm →primary yolk sac

Bilaminar germ disc at 9 th day Primary yolk sac Hypoblast Epiblast Amniotic cavity Syncytiotrophoblast

Bilaminar germ disc Decidua Syncytiotrophoblast Epiblast Hypoblast Primary yolk sac Cytotrophoblast Amniotic cavity

4. Extraembryonic mesoderm: 10 th-11 th day 5. Extraembryonic cavity: 12 th-13 th day Extraembryonic mesoderm: visceral layer parietal layer 6. Secondary yolk sac: 13 th day 7. Body stalk: 14 th day

Embryo at 10 th day Primary yolk sac Extraembryonic mesoderm Germ disc Amnion

Bilaminar germ disc Decidua Epiblast Hypoblast Amniotic cavity Primary yolk sac Cytotrophoblast Extraembryonic mesoderm Syncytiotrophoblast

Embryo at 13 th day Extraembryonic cavity Primary yolk sac Secondary yolk sac Body stalk

Bilaminar germ disc Primary stem villus Extraembryonic mesoderm Visceral layer Extraembryonic mesoderm Parietal layer Body stalk Secondary yolk sac Extraembryonic cavity

Formation of trilaminar germ Trilaminar germ disc primitive streak, primitive groove 3 rd week primitive node, primitive pit 3 rd week 1. Endoderm: primitive groove →hypoblast → endoderm 2. Mesoderm： primitive groove →between epiblast and hypoblat →mesoderm 3. Ectoderm：epiblast →ectoderm

Primitive streak Hypoblast Epiblast

Significance of primitive streak Primitive node l. Determine the Primitive pit direction of the Primitive groove embryo Primitive streak lnotochord

Formation of endoderm Epiblast Primitive streak Endoderm Hypoblast

Formation of mesoderm Epiblast Mesoderm Endoderm

Trilaminar germ disc Ectoderm Mesoderm Endoderm

proliferation Epiblast Head Primitive pit process Notochordal tube Neurenteric canal Significance of notochord ? Notochord

No mesoderm Buccopharyngeal membrane Cloacal membrane

Differentiation of trilaminar germ and formation of embryo Differentiation of trilaminar germ 1. Differentiation of ectoderm ①Neural tube：blastema of CNS neural plate (18 th-19 th day) Neuro-epithelium (neural ectoderm): pseudostratified columnar →neural groove , neural fold → neural tube (closed at 22 nd 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 25 th Neural fold Neural tube closed at 22 nd day, from 4 th somite Posterior neuropore closed at 27 th

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 ①Paraxial mesoderm：somite 17 th day at 20 th 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

Differentiation of lateral mesoderm Dermatome Sclerotome Parietal mesoderm Intraembryonic coelomic cavit Visceral mesoderm

Differentiation of lateral mesoderm Intraembryonic coelomic cavity Extraembryonic coelomic cavity

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 -8 th week) 20 -30 th day Disc folds Column the number of somite increase face development, formation of branchial pouch breach of buccopharyngeal membrane 5 th week: upper and lower limb buds 6 th week: hand foot plates 7 th week: formation of face, disappear of somite 8 th week: breach of cloacal membrane

At the end of 8 th week— a small human

Fetal membrane and placenta Fetal membrane Ø Ø Ø Chorion Amnion Yolk sac Allantois Umbilical cord

Amnion Yolk sac Umbilical cord Placenta

1. Chorion： Secondary stem villus +chorinic plate Primary stem villus： 2 nd week Outer syncytiotrophoblast+ Inner cytotrophoblast Chorinic plate : extraembryonic mesoderm + trophoblast

Secondary stem villus： 3 rd week Outer syncytiotrophoblast+ Intermedial extraembryonic mesoderm+ Inner cytotrophoblast Tertiary stem villus：end of 3 rd week, Blood vessels Anchoring villus, Free villus cytotrophoblastic cell column → cytotrophoblastic shell

Primary stem villus：at 2 nd week，cytotrophoblast Secondary stem villus：at 3 rd week，extraembryonic mesoderm Tertiary stem villus：at the end of 3 rd week，blood vessels

l Stem villus l l Free villus Anchoring villus Cytotrophoblastic column Cytotrophoblastic shell

Evolvement of chorion Chorion laeve：adjacent to decidua capsularis Chorion frondosum： adjacent to decidua basalis 6 th weeks Chorion laeve Chorion frondosum

Abnormility of chorion： Hydatidiform Picture • Chorion carcinoma

Hydatidiform

Chorion carcinoma

2. Yolk sac： 5 th-6 th 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. 5 mm amniotic epithelium + extraembryonic mesoderm amniotic fluid: 500 -1000 ml 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

Placenta 1. Placenta: Chorion frondosum + Decidua basalis disk: 15 -20 cm Sandwich: chorinic plate (fetus) villi basal plate (mother) basal plate: decidua + cytotrophoblastic shell placental septa → cotyledon (incomplete)

Umbilical vein Umbilical artery Decidua bsalis Placenta septa Uterus vein Spiral artery

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

Fetal membrane Syncytiotrophoblast Cytotrophoblast Blood of mother Nutriment Metabolic product 胎儿血 Basal lamina Connective tissue Basal lamina Endothelium

3. Function： ① Substance exchange O 2, nutriment, CO 2, waste ② Hormone Human chorionic gonadotropin, HCG; Human placental lactogen, HPL; Human placental progesterone, HPP, Human placental estrogen, HPE

Placenta Function ① Substance exchange Capillary of fetus 　　　 Blood of mother Ｏ 2 Nutriment water、salt、others ＣＯ 2 Metabolic waste Placenta

Placenta Function ② Barrier Capillary of fetus 　　　 Blood of mother s Most of microorganism No way ！ Placenta barrier

Placenta Function ② Barrier Capillary of fetus 　　　 Blood of mother Most of drugs Most of microorganism Some of microorganism Placenta barrier

Placenta Function ③ Endocrine Hormone HCG HCS Function Corpus luteum Pregnancy Mammary gland Appearance Fastigium 3 rd week 8 th week 2 nd month 8 th month HPE Corpus luteum 4 th month 8 th month HPP Corpus luteum 4 th month 8 th 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 2 Amnion 2 Chorion 2 Placenta

Monozygotic twins separatio n of blastomere, of ICM, of primitive streak Blastocyst 2 ICM 2 Amnion 2 Chorion 2 Placenta 2 Amnion 1 Chorion 1 Placenta 2 primitive streak 1 Amnion 1 Chorion 1 Placenta