Ch16: Embryonic Development

Third week of development ; Trilaminar Germ Disc Department of Anatomy In-je University College of Medicine third week of development 1. Formation of trilaminar embryonic disc Epiblast ectoderm, mesoderm, endoderm gastrulation 2. 3 important structures in germ disc primitive streak, notochord, neural tube 3. 3 part of intraembryonic mesoderm

paraxial mesoderm, intermediate mesoderm, lateral mesoderm 4. 3 cavities amniotic cavity, yolk sac, chorionic cavity 5. Tertiary stem villi formation Primitive Streak Primitive Streak epiblastic cells (bilaminar disc)

primitive streak (primitive groove) primitive node (primitive pit) axial structure Formation of Intraembryonic Mesoderm invagination of epiblastic cells (from primitive streak/groove) proliferation Form mesenchymal tissue invaginate, migrate, organize

Intraembryonic mesoderm hypoblast Some mesenchymal cells embryonic endoderm

Cell remaining in the epiblast embryonic ectoderm Thus the EPIBLAST gives rise to all three germ layers, Ectoderm, Mesoderm, Endoderm in the embryo Each of the three germ layers gives rise to specific tissues and organs Fate of Primitive Streak Actively forms mesoderm until the early part of 4 weeks

Thereafter production of mesoderm slowdown Normally, it degenerates and disappears in sacrococcygeal region ( ) by the end of 4 weeks Notochord mesenchymal cell primitive node

Notochord : - lumen notochordal canal - prochordal (prechordal) plate prochordal plate notochordal process . prochordal plate (oropharyngeal membrane) .

Formation Formation of of notochordal notochordal process process A; 16 - Notochordal process - primitive pit - cardiogenic area - allantois -connecting stalk

C,E; 18 - notochordal canal - neural plate - prochordal plate 18days Formation of notochord primitive pit neuroenteric canal neural groove

notochordal plate neural groove notochordal plate unfolding cloacal membrane in E notochord paraxial mesoderm neural fold intermediate/lateral mesoderm Functions of Notochord

Embryo Embryo . vertebral disc

Fate of Notochord vertebral bodies verterbral disc nucleus pulposus . notochord ectoderm neural plate (induce neural plate) neuroenteric canal notochord Differentiation Differentiation of of the the Intraembryonic Intraembryonic Mesoderm

Mesoderm Induced by the notochord Differentiates (in the region of notochord) into: (Paraxial mesoderm) - somitomere: beyond neural tube and notochord - somite: below occupital level somite stage sclerotome, myotome, dermatome

(Intermediate mesoderm) ; urogenital system (Lateral plate mesoderm) Regions with only ectoderm-endoderm Buccopharyngeal membrane- cephalic end Cloacal membrane- caudal end Neurulation Neurulation neural plate neural fold neural tube 4 neuropore

neurula neural plate - notochord ectoderm neural plate - notochord - Neural plate ectoderm neuroectoderm . neural crest neural tube: 3 (neural folds ) - 4 (neuropores ) neural crest ; neural tube surface ectoderm neuroectoderm cell neural tube Development of Somites 20 days

1. 2. 3. 4. : notochord neural tube mesoderm paraxial mesoderm 3 , paraxial mesoderm somites somite period ( 20-30 ) 38 somites 5 42-44

4-5 embryo 1. 2. : axial skeleton ( , , ) Differentiation of intraembryonic mesoderm & coelom :

lateral mesoderm cardiogenic mesoderm coelomic spaces intraembryonic coelo : lateral mesoderm somatic or parietal layer somatopleure splanchnic or visceral layer splanchnopleure 2 , 3 : pericardial cavity, pleural cavity, peritoneal cavity Somite Somite & &

Intraembryonic Intraembryonic Coelom Coelom A; 18 presomatic embryo - paraxial mesoderm - coelomic space - intraembryonic somatic/splanchnic mesoderm - somite - somatopleure - splanchnopleure

- intraembryonic coelom - pericardial coelom - peritoneal Cardiovascular system 3 , extraembryoinc mesoderm, connecting stalk chorion antiogenesis 2 embryo antiogenesis 3 , primitive uteroplacental circulation 1. Angiogenesis, hematogenesis 2. primitive cardiovascular system

Development of Blood island Angiogenesis & Hematogenesis A; 18 - heart primodium - blood island - primitive blood vessel - lumen of primitive blood Vessel - primitive blood cells - fusion of adjacent vessels

Angiogenesis & Hematogenesis Angiogenesis: 1) angioblast blood islands blood islands 2) angioblast endothelial cells primitive endothelium 3) endothelial channel 4) Hematogenesis:

1) 3 , yolk sac allantois angiogenesis , endothelial cells 2) embryo; 6 , . , , primitive cardiovascular system : 1) mesenchymal cell / 2) 3 , endothelial heart tube 3) 3 , endothelial heart tube , heart tube connecting stalk, chorion, yolk sac primitive cardiovascular system 4) 3 , 5) 21-22 ,

- - 5 , Doppler Development of Chorionic villi Chorionic villi in Placenta Trophoblast

Primary villi cyto, syncytio Secondary villi cyto, syncytio, Mesodermal core

Tertiary villi cyto, syncytio, Endothelium of BV Development of Chorionic villi A; 16 - secondary villus - developing vessels

- chorionic sac C; 21 - tertiary villus - blood vessels - maternal sinusoid - cytotrophoblastic shell Development of Chorionic villi 1. primary chorionic villi : 2 2. secondary chorionic villi : 3 - mesenchymal tissue primary chorionic villi 3. tertiary chorionic villi (stem villi) : 15-20

- , chorion connecting stalk blood vessel Chorionic villi cytotrophoblast syncytiotrophoblast cytotrophoblastic shell

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