The human abdomen is mainly made of the alimentary tract. This is the region where the food is digested and the nutrients are absorbed. The tract is divided into esophagus, stomach, duodenum, jejunum, ileum, cecum, appendix, colon, and rectum.
The other vital organs that are associated with digestion include the liver, kidneys, spleen, and pancreas. The wall of the abdominal cavity (the region above the pelvic inlet and below the thoracic diaphragm) is also segmented by the posterior, lateral, and anterior walls.
The external oblique muscle is the outermost abdominal muscle that shields the sides of the abdomen. This broad and irregularly quadrilateral muscle mass extends from the ribs, curving downwards into the outer anterior ilium crest and the linea alba. The triangular internal oblique muscle is smaller and thinner than the external oblique muscle.
This muscle mass originates in the inguinal ligament and the internal anterior ilium crest. The transversus abdominis muscle wraps the torso from front to back and from ribs to the pelvis. This muscle mass stretches over the ilium, lumbar fascia, and the cartilages of last six ribs, extending till the rectus abdominis.
The rectus abdominis muscle is located inside the abdominals, and is present in the front of the body. It extends from the sternum to the pubic bone. This muscle is worked during crunches, and is also used during childbirth. The other muscle mass in the abdomen is the small and triangular pyramidalis muscle, located in front of the rectus abdominis.
The liver, gallbladder, and pancreas also aid digestion and are connected to the main digestive organs via ducts.
The kidneys, spleen, and adrenal glands are the other organs that are connected via blood vessels like the aorta and inferior vena cava. The human abdomen includes the urinary bladder, uterus, ovaries, and fallopian tubes. These pelvic organs are covered by the same elastic peritoneum membrane that covers most of the abdominal organs.
The abdominal cavity is a major body division of the vertebrate. The wall of the abdomen is a muscular structure, which is lined by fascia, skin, and fat. The organs, muscles, and systems that function within the cavity are studied as part of either the 'abdomen proper' (the upper region) or the 'pelvis' (the lower region).
Though the cavity is not separated or segmented, a bifurcation of function is marked by the superior pelvis aperture. The abdominal wall apertures are the umbilical cord, allantois, vitelline duct, caval opening, aortic hiatus, esophageal hiatus, and lumboinguinal nerve.
In case of males, the rectovesical excavation pouch lies between the rectum and the bladder. In females, the rectouterine excavation pouch is extended over the posterior vaginal fornix.
The peritoneal cavity is distinctly separated from the pleural and pericardial cavities. There is a large coelomic cavity that comprises the viscera and peritoneal sac. All parts of the abdominal cavity are connected via sheets of peritoneum and omenta.
Colloquially called the stomach, the abdomen is an important part of the human anatomy. The shape of a healthy abdomen varies. While in children it protrudes, in young adults it is slightly in-drawn or subtly prominent.