The umbilical vein is a temporary structure that develops during pregnancy. It serves as a conduit, connecting the developing fetus to the placenta. This vessel plays a central role in sustaining fetal life by facilitating the transfer of necessary substances from the mother to her unborn child.
What is the Umbilical Vein?
The umbilical vein is a single, large blood vessel within the umbilical cord. The cord typically contains two umbilical arteries and one umbilical vein, all encased within a protective layer of Wharton’s jelly and surrounded by amnion. Unlike veins in adult circulation, which carry deoxygenated blood, the umbilical vein transports oxygenated blood.
It originates from numerous small veins within the placenta, gathering oxygen- and nutrient-rich blood from the maternal circulation through structures called chorionic villi. From the placenta, it traverses the umbilical cord, enters the fetal abdominal cavity, and travels superiorly within the falciform ligament, a fold of peritoneum, towards the liver.
Its Role in Fetal Development
The primary function of the umbilical vein is to deliver oxygen-rich blood and essential nutrients from the placenta to the growing fetus. This continuous supply is important because the fetal lungs are not yet functional for gas exchange in the womb. The placenta acts as the fetus’s temporary respiratory and digestive system, with the umbilical vein serving as the direct channel for this exchange.
Beyond oxygen, the umbilical vein carries vital nutrients, including glucose, amino acids, and vitamins, all necessary for fetal growth and organ development. Glucose provides the primary energy source for rapid cell division and tissue formation. Amino acids are the building blocks for proteins, which are fundamental for structural development and enzyme synthesis. The consistent delivery of these components supports organogenesis, the formation of organs, and the overall increase in fetal mass. Without a properly functioning umbilical vein, the fetus would lack the necessary resources for healthy development, impacting every system from the brain to the skeletal structure.
How it Connects to Fetal Circulation
Upon entering the fetal body, the umbilical vein’s oxygenated blood embarks on a specialized pathway designed to prioritize delivery to the most sensitive organs. The umbilical vein first reaches the liver, where it typically branches into two main pathways. A smaller portion of this blood supplies the developing liver tissue directly through the portal sinus, ensuring the liver receives its own oxygen and nutrient supply.
The larger portion of the oxygenated blood, however, bypasses the liver through a unique fetal shunt called the ductus venosus. This vessel channels a significant amount of the highly oxygenated blood directly into the inferior vena cava, a large vein that carries deoxygenated blood from the lower body back to the heart. This strategic bypass minimizes the amount of oxygenated blood that passes through the liver, which is not yet fully functional for processing all incoming substances.
Once in the inferior vena cava, the oxygenated blood from the umbilical vein mixes with deoxygenated blood returning from the fetal body. This mixed blood then enters the right atrium of the fetal heart. From the right atrium, a portion of this blood is shunted directly to the left atrium through an opening in the atrial septum called the foramen ovale, bypassing the non-functional fetal lungs. This allows the more oxygenated blood to be pumped by the left ventricle to the fetal brain and upper body, prioritizing these developing structures.
The Umbilical Vein After Birth
After birth, the umbilical vein undergoes natural changes as the newborn transitions from placental to independent circulation. The clamping of the umbilical cord stops the flow of blood from the placenta to the infant. This cessation of blood flow, along with changes in pressure within the circulatory system, triggers the closure of the umbilical vein.
The umbilical vein usually remains open for a short period after the umbilical arteries have closed, allowing for a final transfer of blood from the placenta to the newborn. Within approximately one week of birth, the umbilical vein completely closes and transforms into a fibrous cord. This remnant is known as the round ligament of the liver, or ligamentum teres hepatis. It persists into adulthood as a fibrous band connecting the umbilicus to the liver, running along the free edge of the falciform ligament.