Umbilical cord and fetal circulation
Umbilical cord
It consists of two umbilical arteries and one umbilical vein surrounded by Wharton’s jelly. The umbilical vein carries oxygenated blood while the umbilical artery carries deoxygenated blood.
Fetal circulation
Umbilical vein carries oxygenated blood from the placenta. It divides into the larger ductus venosus and a smaller portal sinus. The ductus venosus bypasses the liver and drains oxygenated blood from the umbilical vein into the IVC. The portal sinus carries oxygenated blood to the liver. Deoxygenated blood from the liver drains into the IVC through the hepatic veins. The fetal right atrium receives partly oxygenated blood from the IVC and deoxygenated blood from the SVC. The foramen ovale connects the RA and LA. Blood further flows from the LA to the LV and reaches the ascending aorta. The aorta then supplies the rest of the body. Most of oxygenated blood reaching the RA is shunted across the foramen ovale to the LA. Most of the deoxygenated blood in the RA is passed on to the RV and pulmonary arteries. As the fetus is not breathing and the pulmonary resistance is high, blood is shunted away from the lungs. The pulmonary artery shunts blood to the descending aorta through the ductus arteriosus. Finally, deoxygenated blood is carried by the umbilical arteries to the placenta for oxygenation.
Organogenesis occurs from 3rd week to 8th week of embryonic period. It is the period most susceptible to teratogenic drugs, toxins and radiation.
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