Notochord
From Embryology
Introduction
(axial mesoderm) The rod of cells lying in the midline of the trilaminar embryo mesoderm layer ventral to the neural tube. Thought to have at least 2 early roles in development and later roles in patterning surrounding tissues. 1. Mechanical, influencing the folding of the early embryo; 2. Morphogenic, secreting sonic hedgehog a protein which regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs). In humans, the notochord forms in week 3 and is eventually lost during the formation of the vertebral column.
