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

Dr. Sherif Fahmy

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

Dr. Sherif Fahmy

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