The belly button, or umbilicus, is a feature present on the abdomen of every placental mammal, yet it often seems to be a feature without a purpose. It is simply the lasting mark, a scar, left behind at the center of the abdomen after birth. While it may appear vestigial now, the umbilicus is the permanent reminder of the structure that made fetal development possible.
The Essential Prenatal Role
Before birth, the connection at the abdomen is an active, multi-functional lifeline known as the umbilical cord. This cord is the conduit between the developing fetus and the placenta, allowing for continuous exchange of materials that sustain life in utero. It is composed of a bundle of blood vessels, typically containing two umbilical arteries and one umbilical vein, all encased in a protective layer called Wharton’s jelly.
The umbilical vein transports oxygenated, nutrient-rich blood from the placenta directly into the fetal circulatory system. The two umbilical arteries carry deoxygenated blood and metabolic waste products from the fetus back to the placenta. Within the placenta, these waste products, such as carbon dioxide, are transferred into the mother’s circulation for elimination. Without this bidirectional system, which functions as the fetus’s temporary respiratory, digestive, and excretory organ, growth and survival would be impossible.
The Transition and Formation
The formation of the navel begins immediately after birth when the newborn no longer relies on the placenta for life support. A healthcare provider clamps and cuts the umbilical cord, a painless procedure because the cord contains no nerve endings. This leaves a small remnant attached to the baby’s abdomen, referred to as the umbilical stump.
The stump then begins a natural process of degradation. Over the next one to three weeks, the stump dries out, shrivels, and changes color from a yellowish-green to brown or black. Once the tissue completely dries, the stump detaches on its own, revealing the healed area beneath. The resulting structure, the belly button, is entirely scar tissue. Whether a person has an “innie” (inverted) or an “outie” (protruding) is determined by how the skin heals and the amount of underlying tissue, not by how the cord was cut.
Does the Navel Serve a Purpose Now?
Once the umbilical cord stump has healed, the navel serves no direct biological function for survival or bodily processes in the adult body. The blood vessels within the cord remnant close off and transform into ligaments inside the abdomen, becoming integrated with the inner abdominal wall.
Despite its lack of physiological necessity, the navel does have utility in the medical field. It provides a consistent anatomical landmark, marking the center of the abdomen, which is useful for physical examinations and dividing the abdomen into quadrants. More significantly, the navel is frequently used as the primary access point for minimally invasive laparoscopic surgery. Surgeons utilize the natural opening in the abdominal wall at this location to insert instruments, which helps to conceal the surgical scar.