Answer
The umbilical cord is the connection between the fetus and the placenta. It consists of connective tissue and endothelium ( with mesenchymal stem cells) which supports jelly-like matrix called Wharton's Jelly.
Three umbilical blood vessels pass through the umbilical cord; one large umbilical vein to the fetus and two umbilical arteries from fetus to placenta. The umbilical vein carries oxygenated blood and nutrients to the fetus. Poorly oxygenated blood plus wastes are transported out of the fetus to the placenta by two umbilical arteries.
Work Step by Step
Functional Exchange:
As placentation begins extensions of the syncythiotrophoblast sends chorionic extensions (villi) into the endometrium. Chorionic villi penetrate endometrial blood vessels and become surrounded by lacunae of maternal blood. With nourishment from the blood, chorionic villi grow rapidly; later extra embryonic mesoderm grows into the villi and eventually form blood vessels. These blood vessels connect embryo and placenta by way of the umbilical cord.However, there is no mixing of the two circulations( fetal and maternal). Nevertheless the thin membrane that separates the two circulations permit diffusion; the membrane becomes thinner as the chorionic villi grow and branch. The result is a progressive increase in permeability of the chorionic membrane and the rate of diffusion of substances through it. Consequently , the rate of diffusion of substances increases from one side to the other down concentration gradients. Oxygen and nutrients diffuse from maternal blood to fetal blood and carbon dioxide and metabolic wastes diffuse from fetal blood to maternal blood to be eliminated by the mother.
