gastrulation & notochord (general embryology)
TRANSCRIPT
Decidua basalis
Chorion frondosum
Chorionic plate
Chorion leave
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Development of Trilaminar Embryonic
Disc
Gastrulation
Dr. Sherif Fahmy
GastrulationIt begins by formation of:1- Primitive streak.2- Primitive node.3- Bucco-pharyngeal membrane.4- Cloacal membrane.
Dr. Sherif Fahmy
Syncytiotrophoblast
CytotrophoblastSomatic extra-embryonic mesoderm
Amniotic cavity
Buccopharyngeal membrane
Primitive node & pit
Primitive streak
Cloacal membraneDr. Sherif Fahmy
Yolk sac
Hypoblast
Epiblast
Dr. Sherif Fahmy
Invagination- Epiblast cells migrate to primitive streak.-Then they pass beneath epiblast to become flask-shaped and separated from the epiblast and form:1- Endoderm that replaces the hypoblast.2- Third layer between epiblast and endoderm which consists of intra-embryonic mesoderm with notochord in the median region..3- Remaining epiblast cells after formation of notchord and intraembryonic mesoderm will be named ectoderm.
Primitive streakPrimitive node and pit
Epiblast
Hypoblast
Invaginating cells from epiblast lyaer
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Formation of Notochord
Amniotic cavity
Embryonic disc
Secondary yolk sac
Amniotic cavity Buccopharyngeal membrane Primitive pit
Cloacal membrane
Connecting stalk
Connecting stalk
Notochord under ectoderm
Dr. Sherif Fahmy
Primitive streak
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Amniotic cavity
Epiblast
1-Notochordal
process
Primitive pit
Primitive streak
Connecting stalk
Secondary yolk sac
Endoderm that replaced hypoblast
AllantoisBucco-pharyngeal membrane
Dr. Sherif Fahmy
Notochordal process
2-Notochordal
canal
Primitive streak
Connecting stalk
Allantois
Dr. Sherif Fahmy
2-Notochordal
canal
Cloacal membrane
Allantois
Buccopharyngeal membrane
Dr. Sherif Fahmy
Amniotic cavity
Yolk sac
3-Degenerating endoderm and floor of notochordal canal
Roof of notochordal canal
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Neurenteric canal
Buccopharyngeal membrane
Cloacal membrane
Dr. Sherif Fahmy
Extraembryonic mesodermNotochorda
l canal
Intraembryonic mesoderm
Epiblast (Ectoderm)
Endoderm
Dr. Sherif Fahmy
Notochordal plate
Notochordal plate (roof of the canal intercalate (fixed) to endodermal layer.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Notochord
Dr. Sherif Fahmy
Development of Notochord• 1- Pre-notochordal process: Proliferation of cells from
primitive pit forms a cord of cells in median plane till prochordal plate.
• 2- Notochordal canal: Canalization of the process forms notochordal canal.
• 3- Notochordal-ectodermal fusion: fusion between floor of the canal and endoderm.
• 3- Neur-enteric canal: Temporary communication between amniotic cavity and yolk sac due to degeneration of floor of notochordal canal and underlying endoderm.
• 4- Defenitive notochord: Regeneration of endoderm only. Persistent roof of notochordal canal becomes folded upon itself to form defenitive notochord.
Dr. Sherif Fahmy
Fate of Notochord
• It is the primitive axial skeleton around which the vertebral column is formed.
• It remains in intervertebral disc as nucleus pulposus.
Dr. Sherif Fahmy
Dr. Sherif Fahmy