The belly button, or navel, is a distinct scar located on the abdomen. It marks the precise point where the umbilical cord once connected a developing fetus to its mother during pregnancy. After birth, it serves no functional purpose.
The Navel’s Fetal Connections
During fetal development, the umbilical cord functions as a lifeline, facilitating the exchange of nutrients, oxygen, and waste products between the mother and the fetus. This cord typically contains three primary vessels: one umbilical vein and two umbilical arteries. The umbilical vein transports oxygenated, nutrient-rich blood from the placenta to the fetus, while the two umbilical arteries carry deoxygenated blood and waste products away from the fetus back to the placenta.
After birth, when the umbilical cord is cut, these vessels are no longer needed and undergo a natural process of obliteration and transformation. The umbilical vein typically closes within a week after birth, forming a fibrous cord known as the round ligament of the liver, or ligamentum teres hepatis. This ligament extends from the navel to the liver.
Similarly, the umbilical arteries also obliterate after birth. The distal portions of these arteries become the medial umbilical ligaments, which are fibrous cords extending from the navel towards the pelvis. Another important fetal connection is the urachus, a tubular structure that linked the fetal bladder to the umbilical cord. This connection normally closes before birth, becoming the median umbilical ligament, which runs from the navel to the top of the bladder. These transformed structures are the primary remnants directly behind the navel from its developmental origin.
Structures of the Abdominal Wall
The navel is embedded within the layers of the abdominal wall, which provide a protective barrier for the internal organs. From the outermost to the innermost, these layers include the skin, followed by subcutaneous tissue, which is composed of fatty and membranous layers.
Beneath these superficial layers lie several muscles, including the rectus abdominis and the oblique muscles, along with their associated fascial sheaths. The rectus abdominis muscles are paired vertical muscles, with the navel typically located within their midline. Further inward is the transversalis fascia, a thin but strong connective tissue layer.
The deepest layer of the abdominal wall is the peritoneum, a thin serous membrane that lines the abdominal cavity and covers many of the abdominal organs. The fibrous remnants of the umbilical cord structures are embedded within or attached to these fascial and peritoneal layers directly behind the navel. While the abdominal cavity contains organs such as the intestines, these organs are not directly attached to the navel itself; rather, they are housed within the cavity protected by these multiple layers of the abdominal wall.