The abdomen is that part of the torso which lies between the diaphragm and the pelvis. It is commonly referred to as the stomach, belly or "tummy." Inside the abdominal cavity are a number of important organs, including the liver, pancreas, spleen and kidneys. A large part of the digestive tract is also found there, including the stomach, and the small and large intestine. The aorta, a major artery, runs vertically through the abdominal cavity.
Separating the upper abdomen from the chest is the diaphragm, a dome-shaped muscular wall involved in respiration. Below, the lower abdomen is continuous with the pelvis. At the front, the abdomen consists of layers of muscles which make up the abdominal wall. The rear abdominal wall is made up of muscles of the back, together with part of the spine. Externally, the abdomen is covered in skin with an underlying layer of fat.
The navel or umbilicus, a scar where originally the umbilical cord was attached to the fetus, is usually found in the midline of the abdomen and can often become infected due to poor hygiene. Seen from the front, the appearance of the abdominal wall depends greatly upon the condition of the underlying muscles. Poor muscle tone typically results in abdominal protrusion.
Abdominal pain is very common and not usually caused by severe illness. Sometimes extreme pain is felt due to a harmless problem, such as gas inside the gut or a gastrointestinal infection. Alternatively, little or no pain may be associated with serious conditions such as cancer.
Disorders of any of the abdominal organs may give rise to pain. A common example is the appendix, a small pouch in the large intestine which may be infected by bacteria from the gut, becoming inflamed and full of pus. Without treatment, the appendix might burst, releasing its contents into the abdominal cavity to cause a life-threatening condition known as peritonitis.
Correctly diagnosing the abdominal pain associated with appendicitis means that the appendix can be surgically removed, preferably before it bursts. Although symptoms are not always typical, most often the pain begins suddenly in the center of the abdomen and moves, over the next few hours, to an area on the lower right. The pain can be extreme and may be associated with fever, nausea, constipation and a need to pass urine frequently.
A swollen abdomen may be a sign of something normal, such as weight gain or intestinal gas, or might occasionally indicate illness. Fluid accumulating abnormally inside the abdominal cavity is known as ascites. It can occur in liver disease and some cancers, and treatment varies depending upon the cause.