General embryology : Development of Notochord

 

Development of Notochord 

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It is the primordial longitudinal axis of the embryo extends from the cranial end of primitive streak to prochordal plate.  Around the notochord the axial skeleton is formed.

Time period of formation

Start from 16 days, and  is completely formed by the beginning of the fourth week.

Fate of notochord

It is disappears but its remnants are persists as the nucleus pulposus of the intervertebral disks and apical ligament of dens of 2^nd cervical vertebra.

Importance of notochord

The notochord is the defining structure of the phylum chordates, and has essential roles in vertebrate development.

Functions of notochord

It acts as organizer and induces the development of neural tube.

It forms the central axis of developing embryo.

It serves as the basis for the axial skeleton (vertebral column) but the notochord does not give rise to the vertebral column.

Formation of notochord

1.     Appearance of primitive streak

2. The primitive streak's cranial end proliferates to form a primitive node

3. Cells in the primitive node multiply and migrate cranially between the ectoderm and endoderm, eventually reaching the prochondral plate. The notochondal process is a solid cord of tissue.

4. A small depression called a primitive pit develops in the primitive node and extends into the notochordal process, converting it to a notochordal canal.

5. The notochordal canal's floor fuses with the endoderm. Then it crumbles and form the neuroenteric canal which communication with the amniotic cavity and the yolk sac cavity.

7. The remainder of the notochordal canal flattens and forms the notochondal plate.

8. The notochordal plate folds and forms a tube

9. Tube cell proliferation results in the formation of a cord known as the definitive notochord.