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The navel, also known as the belly button or umbilicus, is the scar on your abdomen from where the umbilical cord was attached during gestation. It generally serves little biological purpose after birth, other than as a cosmetic feature on the abdomen. However, the navel does have some functions:
– It is an external mark of where the umbilical cord was connected. This can be useful for medical diagnosis of certain abdominal problems related to development.
– It harbors abdominal skin flora, which may play a role in establishing the immune function of the skin.
– In rare cases, the urachus does not fully close after birth and a small canal persists at the navel. This can result in leakage of urine from the navel.
– The navel can be an erogenous zone. Stimulation of the nerves that line the navel may produce pleasurable sensations.
Formation of the Navel
The navel begins forming early in fetal development. At about 4 weeks gestation, the embryo begins folding ventrally and the lateral folds move to surround a portion of the yolk sac. This folding forms the anterior abdominal wall and creates a small depression, the beginning of the umbilicus.
By 10-12 weeks gestation, the abdomen has completely closed and the umbilical ring has formed. The umbilical ring is the opening in the abdomen that allows passage of the umbilical cord. It is located at the future site of the navel.
As the fetus grows, the amniotic fluid surrounding it expands and pushes out on the umbilical ring. This causes the fetus’s skin to balloon out, covering the umbilical cord. By 20 weeks gestation, the skin has fully covered the cord, forming the umbilical stalk.
After birth, the severed umbilical cord dries and falls off within a couple weeks, leaving behind the navel. Initially, the navel appears large and protruding. Over time, it becomes a depressed scar due to the skin contracting. In adults, the navel is usually an inward-facing scar.
Variations in Navel Appearance
Since the navel forms from the scar of the severed umbilical cord, there can be considerable variation in its shape, size, and depth between individuals:
– Shape – Navels can be round, vertical, horizontal, or irregularly shaped.
– Size – Diameter ranges from small (less than 1.5 cm) to large (over 3 cm).
– Depth – Shallow to extremely deep navels occur. Protruding navels that stick out can also form.
– Number of holes – Normally a single navel opening. But duplication is possible, either side-by-side or vertically.
– Position – Usually centrally located on the abdomen above the pubic region. But may be tilted sideways.
– Appearance – Unique creases, folds, or scar patterns occur around each individual’s navel. Accessory nipples or hair growth around the navel is also possible.
This wide variation results from differences in cord length, cord thickness, amount of fat, abdominal pressure, and healing. Conditions like obesity or multiple pregnancies can also affect navel formation. Despite the variation, the basic internal structure of the navel and surrounding tissues is similar.
Internal Structure of the Navel
Though it appears to be just a depression in the skin, the navel is a complex scar with deeper internal structures:
– Skin – The external skin. Pigmentation, hair growth, and superficial blood vessels are present.
– Subcutaneous tissue – A layer of fat and connective tissue. Contains larger blood vessels and nerve fibers.
– Fascia – A layer of fibrous, connective tissue that covers the abdominal muscles.
– Peritoneum – The membrane lining the abdominal cavity that covers the internal organs.
– Urachus – A fibrous remnant of the umbilical cord. Located on the inside surface of the abdominal wall. Extends from the navel to the top of the bladder.
– Medial umbilical ligaments – Paired remnants of the umbilical arteries. Extend from the navel on each side of the bladder to the pelvic crest.
– Lateral umbilical ligaments – Paired remnants of the umbilical veins. Run along the internal surface of the abdominal wall.
– Remnant umbilical ring – The internal scar marking where the umbilical cord passed through the abdomen. This is the deepest part of the navel.
This complex internal structure anchors the navel to the abdominal wall. The urachus and ligaments help anchor and stabilize the bladder.
Functions of the Navel
Though a largely vestigial structure, the navel does serve several biological functions:
External Landmark
The navel acts as visual marker of where the umbilical cord was connected during development. This can provide some diagnostic information about abdominal abnormalities:
– High or low position indicates problems with ventral closure.
– Off-center navels may indicate muscle or organ defects.
– Duplicated navels can indicate conjoined twinning that failed to fully separate.
– Enlarged, stretched navels are associated with large abdominal growths during development.
Microbial Habitat
The moist folds and crevices of the navel provide an ideal habitat for colonization by microorganisms. Up to 65 bacterial species may inhabit the average navel. Some of the most common include:
– Corynebacteria
– Staphylococci
– Bacilli
– Micrococci
This specialized microbial community interacts with the immune cells present in the skin. It provides stimulation to develop and maintain proper immune function.
Individuals who undergo ostomy surgery to remove their navels lose this microbial ecosystem. They can suffer impaired immune regulation as a result.
Connection for Urachal Abnormalities
Normally, the urachus closes before birth and degenerates into a fibrous cord. But in a small percentage of people, a portion of the lumen remains patent.
This urachal anomaly results in a tunnel extending from the bladder to the umbilicus. Problems can occur if this tunnel becomes infected or allows urine leakage through the navel. Surgical removal of the umbilicus may be required to correct urachal abnormalities.
Erogenous Zone
In some individuals, the navel can function as an erogenous zone. This heightened sensitivity results from several factors:
– Rich nerve supply – Spinal nerves T7-T12 supply the abdominal wall around the navel. Stimulation of these nerves produce pleasurable sensations that can be perceived as erotic.
– Emotional associations – Because the navel visually demarcates the abdomen, it can be closely associated with sexuality in some cultures. Licking or touching of the navel is seen as an intimate act.
– Navel fetishism – A sexual paraphilia in which the navel is highly fetishized and eroticized. Individuals with navel fetishism are intensely attracted to the look, smell or taste of navels.
However, due to habituation and desensitization from clothing friction, not all individuals are erotically sensitive at the navel. The degree to which the navel functions in sexual arousal varies.
Clinical Importance of the Navel
Though mostly cosmetic, the navel and umbilicus do have some clinical significance for physicians. These include:
Assessing Developmental Problems
The position and appearance of the navel provides information about possible ventral body wall defects. These include:
– High or low navel position indicating failure of complete closure.
– Off-midline navel indicating uneven muscle development.
– Distorted or duplicated navel indicating imperfect fusion of multiple embryos.
Treating Urachal Cysts
Improper closure of the urachus can lead to patent connections between the bladder and navel. Urine drainage, stone formation, and infections may occur. Surgical removal of the cysts via the navel may be required.
Identifying Hernias
Hernias involving protrusion of abdominal contents can sometimes protrude at the navel. Omphaloceles exhibited by infants are hernias of intestinal contents exiting through the umbilicus.
Accessing Abdominal Wall
Surgical procedures on the abdominal wall, like hernia repair or abdominal wall reconstruction, may utilize the navel for instrument access to minimize visible scarring.
Navel Piercing Complications
Piercings and jewelry placed through the navel can cause infections. Abscesses and drainage need to be diagnosed and treated. Foreign body rejection and excessive scarring can also occur with navel piercings.
Assessing Skin Lesions
Unusual skin findings around the navel may indicate inflammatory conditions, infections, or superficial tumors that require dermatologic diagnosis.
Cleaning Before Surgery
The deep folds around the navel harbor bacteria and need to be thoroughly cleaned before any abdominal surgery to reduce infection risk.
So while the navel may seem an innocuous structure, it has importance for doctors assessing developmental abnormalities, conducting abdominal procedures, and preventing skin infections.
Cultural Significance of the Navel
Beyond its biological functions, the navel has developed cultural and aesthetic significance across many societies:
Mark of Femininity
Its presence on the smooth, flat surface of the abdomen makes the navel a prominent female physical feature. It is celebrated in arts, dress, and decorations that draw attention and emphasize the belly.
Cosmetic Enhancement
Various procedures surgically alter the navel for perceived cosmetic improvement. These include navel repositioning, reshaping, and size reduction.
Body Adornment
Navels provide a visible location for body art and piercings. Rings, bars, and other jewelry in the navel are common fashion statements. Temporary navel decoration like glitter and henna are also applied.
Clothing Accentuation
Designs that reveal or highlight the waistline call attention to the navel. This includes exposing the midriff, naval cleavage windows in tops, and jeweled accents in the navel area.
Danse du ventre
Belly dancing originated as traditional Middle Eastern dance emphasizing complex movements of the torso and abdomen. It draws focus to the navel and hip gyrations.
Fetishism and Erotica
The navel is heavily fetishized in sexual subcultures. Swabhava, an Indian religion, even uses navel worship in its spiritual practice.
So while medically vestigial, the navel retains cultural, aesthetic, and erotic significance that seems likely to persist.
Conclusion
The navel develops prenatally as the scar left from the detachment of the umbilical cord after birth. Though largely a cosmetic remnant, the navel does retain some minor biological functions related to abdominal development, microbiome habitat, urachal anomalies, and erogenous sensitivity. However, its key significance arises from the cultural and aesthetic importance placed on its symbolic location on the abdomen and waist. The allure of the navel has been celebrated, fetishized, and embellished across many human societies.
