The umbilical artery is a vital vessel that primarily functions during fetal development, carrying deoxygenated blood from the fetus to the placenta. In the adult body, after birth, most of the umbilical artery becomes obliterated and forms the medial umbilical ligament, with only a portion remaining patent to supply the bladder.
Location
During fetal development, the umbilical artery originates from the internal iliac arteries and runs along the inner surface of the anterior abdominal wall, extending toward the umbilicus and into the umbilical cord, where it connects to the placenta. After birth, the distal portion of the artery closes and forms the medial umbilical ligament, while the proximal portion remains functional as the superior vesical artery, which supplies the upper part of the bladder. The artery’s remnants are located in the pelvis and the anterior abdominal wall.
Structure and Anatomy
The umbilical artery is an important vessel in fetal development and later transforms in its function postnatally. It originates from the internal iliac arteries and is a key part of fetal circulation. Below is a detailed description of its anatomy during fetal life and its transformation after birth.
Fetal Anatomy of the Umbilical Artery
During fetal life, the umbilical artery plays a crucial role in carrying deoxygenated blood from the fetus to the placenta for gas and nutrient exchange. There are two umbilical arteries, each arising from the anterior division of the internal iliac artery on both sides of the fetal pelvis.
- Course in the Fetus: After branching from the internal iliac arteries, the umbilical arteries ascend along the lateral walls of the pelvis. They then travel forward along the inner surface of the anterior abdominal wall. At the umbilicus (belly button), the umbilical arteries exit the fetal body and enter the umbilical cord, where they run alongside the single umbilical vein to reach the placenta.
- Umbilical Cord: Inside the umbilical cord, the two umbilical arteries spiral around the umbilical vein, extending to the placenta, where they facilitate the transfer of deoxygenated blood from the fetus to the maternal circulation for oxygenation and waste removal.
Postnatal Changes
After birth, when the umbilical cord is cut and the placenta is no longer needed for oxygen and nutrient exchange, the umbilical arteries undergo a significant transformation.
- Medial Umbilical Ligament: The distal portions of the umbilical arteries, which extend from the bladder to the umbilicus, become obliterated and are replaced by fibrous tissue, forming the medial umbilical ligament. This ligament runs along the inner surface of the anterior abdominal wall, tracing the original course of the fetal umbilical arteries toward the umbilicus.
- Patency of the Proximal Part: The proximal part of the umbilical artery, which is the segment closest to the internal iliac artery, remains functional in adults. This portion stays open and continues to supply blood to the superior part of the bladder. It becomes part of the vascular system responsible for bladder perfusion, specifically contributing to the superior vesical artery.
Branches
In the fetal period, the umbilical artery does not give off major branches until it reaches the placenta, where it interacts with the placental capillary network. After birth, the proximal portion of the artery that remains patent forms branches, including the superior vesical arteries, which supply the bladder and nearby structures.
Relations to Other Structures
- In the Fetus: The umbilical arteries are closely associated with the umbilical vein within the umbilical cord. They are surrounded by Wharton’s jelly, a gelatinous substance that protects these vessels during fetal development.
- In Adults: The remnants of the umbilical artery, in the form of the medial umbilical ligaments, run on either side of the bladder and are closely related to the anterior abdominal wall. The proximal patent portion of the artery lies near the internal iliac artery, contributing to the pelvic vascular network.
Variations
The umbilical arteries are typically present as a pair in the fetus. However, in some rare cases, there may be a single umbilical artery, which can occur due to developmental abnormalities. This condition may be associated with other congenital anomalies but still carries out the essential function of fetal blood transport.
Function
The umbilical artery serves a critical role during fetal development and undergoes functional changes after birth. Below is a detailed explanation of its functions in both the fetal and postnatal periods.
Fetal Circulation
During fetal life, the umbilical artery is a key component of the circulatory system, responsible for carrying deoxygenated blood from the fetus to the placenta. The placenta is where the exchange of oxygen, carbon dioxide, nutrients, and waste occurs between the mother and fetus. The umbilical artery ensures that this vital exchange takes place effectively.
- Transport of Deoxygenated Blood: The primary function of the umbilical artery is to transport blood low in oxygen and nutrients from the fetal circulation to the placenta. The placenta then oxygenates the blood and removes waste products such as carbon dioxide. The nutrient-rich, oxygenated blood is returned to the fetus via the umbilical vein.
- Placental Exchange: The umbilical arteries form part of a vascular network that allows for the proper exchange of gases, nutrients, and waste between fetal and maternal blood. The artery carries blood to the placental villi, where the exchange occurs across a thin membrane separating maternal and fetal blood supplies.
Role in Fetal Waste Removal
The umbilical artery also plays a critical role in removing metabolic waste products from the fetus. As blood is transported to the placenta, substances such as carbon dioxide and nitrogenous wastes (urea) are carried along to be exchanged and removed via the mother’s circulation.
- Removal of Carbon Dioxide: Blood rich in carbon dioxide, a waste product of fetal metabolism, is transported by the umbilical artery to the placenta, where it is exchanged for oxygen.
- Excretion of Nitrogenous Wastes: The umbilical artery also carries other waste products, including urea and creatinine, from the fetus to the placenta for excretion by the maternal kidneys.
Postnatal Role: Formation of the Medial Umbilical Ligament
After birth, when the umbilical cord is cut and the placenta is no longer needed, the distal portion of the umbilical artery closes and transforms into a fibrous structure known as the medial umbilical ligament. This structure no longer functions as a blood vessel but remains as a remnant of the fetal circulatory system.
Formation of the Medial Umbilical Ligament: The umbilical artery becomes fibrotic and forms the medial umbilical ligament, a vestigial structure that runs along the anterior abdominal wall toward the umbilicus. Though it no longer serves a vascular function, this ligament is a key anatomical landmark in the pelvic region.
Postnatal Role: Blood Supply to the Bladder
The proximal portion of the umbilical artery, which remains open after birth, serves an important function in the adult body by contributing to the blood supply of the bladder. The portion of the umbilical artery that remains patent continues to function as the superior vesical artery, which provides oxygenated blood to the upper part of the urinary bladder and the ureter.
- Bladder Perfusion: The patent segment of the umbilical artery plays an essential role in perfusing the superior aspect of the bladder, ensuring that the bladder has sufficient blood flow to support its function in storing and expelling urine.
- Ureteral Blood Supply: This artery also contributes small branches that supply blood to the distal portion of the ureter, which connects the kidneys to the bladder, facilitating proper urinary function.
Redundant Blood Supply in the Pelvis
The umbilical artery, through its transformation into the superior vesical artery, contributes to the redundant vascular supply of the pelvic organs. This redundancy ensures that in cases of damage to other pelvic arteries, blood flow to vital organs like the bladder and ureter can be maintained through collateral circulation.
Anastomoses with Other Arteries: The superior vesical artery, which is derived from the umbilical artery, forms important connections (anastomoses) with other pelvic arteries, providing additional routes for blood flow in the pelvis.
Variations and Function in Congenital Anomalies
In cases where only a single umbilical artery is present (instead of the usual two), the remaining artery must carry out the full function of transporting deoxygenated blood from the fetus to the placenta. Although a single umbilical artery can still perform the necessary functions, this condition may sometimes be associated with other congenital abnormalities.
Compensation in Single Umbilical Artery Cases: When a single umbilical artery is present, it must compensate for the absence of the second artery, ensuring that sufficient blood flow is maintained to support fetal development.
Clinical Significance
The umbilical artery plays a crucial role during fetal development, and its clinical significance extends to both prenatal and postnatal care. During pregnancy, Doppler ultrasound is often used to assess the blood flow in the umbilical arteries. Abnormal flow patterns in these arteries can indicate issues such as intrauterine growth restriction (IUGR) or placental insufficiency, which may signal complications in the pregnancy.
After birth, the medial umbilical ligament, a remnant of the umbilical artery, serves as an important anatomical landmark in pelvic surgeries. In the adult body, the proximal portion of the umbilical artery remains functional as the superior vesical artery, supplying blood to the bladder. This artery’s patency is important in bladder surgeries, such as in cases of bladder cancer or reconstructive procedures, where maintaining adequate blood supply is critical for healing.
