The belly button, medically known as the umbilicus or navel, represents the most noticeable scar on the human body. This small depression or protrusion is the physical result of the umbilical cord detaching shortly after birth. It marks the point where a temporary but complex biological system once connected the developing fetus to the placenta. While the external mark is scar tissue, it signifies the location of former internal structures whose function ceased when independent life began.
The Prenatal Connections of the Umbilical Cord
Before birth, the umbilical cord serves as the sole lifeline, acting as the conduit for all necessary exchange between the mother’s placenta and the fetus. This structure contains a specialized set of blood vessels protected by Wharton’s jelly. The cord typically houses three distinct vessels: one large umbilical vein and two smaller umbilical arteries.
The single umbilical vein carries oxygenated and nutrient-rich blood directly from the placenta into the fetus’s circulatory system. Conversely, the two umbilical arteries transport deoxygenated blood and metabolic waste products back from the fetus to the placenta for processing. This arrangement is unusual, as veins typically carry deoxygenated blood and arteries carry oxygenated blood in the adult body.
The cord also contains the remnants of the allantois, which forms a tube known as the urachus that connects the developing bladder to the umbilical region. Wharton’s jelly prevents the vessels from collapsing or kinking inside the womb. Once the baby is born, its own lungs and digestive system take over the work of the placenta, rendering the umbilical cord functionally obsolete.
What Remains Connected in Adulthood
The shift in circulation at birth causes these active vessels and conduits to quickly close off and atrophy. The internal portions of the umbilical vessels are transformed into dense, fibrous cords that persist into adulthood. These fibrous remnants anchor the navel to deeper abdominal structures and are the true internal connections of the adult belly button.
The single umbilical vein shrinks down to become the Round Ligament of the Liver (Ligamentum teres hepatis). This ligament runs from the umbilicus up toward the liver, attaching to its underside. The two former umbilical arteries also obliterate, turning into the Medial Umbilical Ligaments.
These two medial ligaments extend downward and outward from the navel region toward the sides of the bladder. A third connecting cord, the Median Umbilical Ligament, is formed from the remnant of the urachus, running from the top of the bladder to the umbilicus. These three sets of ligaments—the median and the two medial—form a structural framework beneath the skin of the lower abdomen.
These ligaments are no longer active vessels but serve to reinforce the abdominal wall and hold certain internal organs in place. They represent the final anatomical result of the prenatal circulatory and excretory paths. This fibrous tissue secures the umbilicus to the deeper abdominal fascia.
Common Issues and Anatomical Weaknesses
The area around the umbilicus represents a natural point of weakness in the abdominal wall due to the penetration of fetal vessels during development. This region is prone to developing structural defects even in adulthood. The most frequent issue is an umbilical hernia, which occurs when abdominal contents, such as fat or intestine, protrude through the weakened muscular layer.
Umbilical hernias are frequently seen in infants, but they also occur in adults due to conditions that increase pressure within the abdomen. Factors such as obesity, multiple pregnancies, or chronic straining can place excessive stress on this compromised area. The weakness often lies in the fascia surrounding the umbilical ring, which does not fully close or is stretched over time.
The navel’s shape makes it susceptible to accumulation of skin debris and bacteria. Poor hygiene can lead to infections (omphalitis) or the formation of keratin and sebum plugs, known as “navel stones.” Rarely, remnants of the fetal urachus fail to completely close, leading to persistent draining or cyst formation.