It is made up of:
Amniotic Epithelium: A simple cuboidal epithelium covers the outside of the amniotic sac.
Blood Vessels: The fetus and the placenta share oxygen, nutrients, and waste products through the blood vessel
Two umbilical arteries carry blood from the fetus to the placenta that has lost oxygen.

Single Umbilical Vein: Blood with oxygen from the placenta goes to the fetus through this vein. It is different from adult veins in that it has a thick layer of circular smooth muscle.
In Wharton’s Jelly, the blood vessels are embedded in a matrix of embryonic mucous connective tissue.
Most of the material is ground up (mostly hyaluronic acid and chondroitin sulfate), and there isn’t much collagen or reticular fiber in it.

Mesenchymal Cells: There are a lot of stellate and spindle-shaped (fusiform) mesenchymal cells near where the allantois used to be. But spindle-shaped mesenchymal cells look the same as fibroblasts when they are at rest.