The umbilicus, commonly known as the belly button, is a unique and permanent scar marking where the umbilical cord connected an individual to the placenta during fetal development. This distinct feature appears on the abdomen after birth, following a natural healing process. The umbilicus represents the closure of a former passageway for vital blood vessels and provides a window into the complex physiological journey of early life.
Anatomy and Formation of the Umbilicus
The formation of the umbilicus begins immediately after birth when the umbilical cord is clamped and cut, leaving behind the umbilical stump. This stump, typically two to three centimeters long, is composed of remnant blood vessels and connective tissue. Over the next one to three weeks, the stump naturally shrivels, dries, and separates from the body.
Once the stump falls off, the remaining wound gradually heals to form the umbilicus. The final appearance is a fibrous scar where the skin adhered to the underlying abdominal wall. Internally, the umbilicus is a junction point for several fetal structures that solidify into ligaments. The former umbilical vein becomes the round ligament of the liver, while the two umbilical arteries harden into the medial umbilical ligaments.
The Role of the Umbilical Cord
Before the umbilicus exists as a scar, the umbilical cord serves as the sole physical lifeline between the developing fetus and the placenta. Its function is to support fetal circulation, acting as a two-way conduit for respiratory and nutritional exchange. The cord typically contains three blood vessels: one umbilical vein and two umbilical arteries, all protected by a firm, gelatinous substance known as Wharton’s jelly.
The single umbilical vein carries oxygenated and nutrient-rich blood from the placenta directly to the fetus. Conversely, the two umbilical arteries transport deoxygenated blood and metabolic waste products, such as carbon dioxide and urea, from the fetus back to the placenta. This constant, bidirectional traffic ensures the fetus receives everything it needs until its own systems can take over after birth.
Common Umbilical Variations and Health Concerns
The final shape of the umbilicus, whether concave (“innie”) or convex (“outie”), is determined by the natural process of scar formation and how the skin adheres to the abdominal fascia. This variation is largely a matter of chance and individual healing, and it is not influenced by how the cord was clamped or cut. Approximately 90% of people have an innie, while 10% have an outie.
Sometimes, an outie appearance is caused by a medical condition, most commonly an umbilical hernia. This occurs when a small opening in the abdominal muscles near the navel remains, allowing tissue to push through and cause a bulge. Umbilical hernias are common in newborns and frequently close on their own without intervention, often by the age of five.
Another concern, particularly in infants, is omphalitis, a bacterial infection of the umbilical stump or surrounding tissue. Signs of this rare infection include redness, tenderness, and yellowish discharge with a foul odor, which warrants prompt medical attention. Good hygiene, involving keeping the area clean and dry, is the best way to encourage healthy healing of the stump and prevent infection.