The abdomen consists of the organs necessary for digestion. These include the stomach, pancreas, liver, gallbladder and small and large intestines. The abdomen also contains the kidneys and spleen. Connecting tissues called the mesentery, hold these organs together. The mesentery also allows these organs to move relative to one another and expand. The abdomen has a covering fascia, a layer of tissue that is protective. The abdominal muscles lay in front of the fascia, and on the outermost layer is the skin. The back of the abdomen consists of back muscles as well as the spine.
The junction where the abdomen ends and the pelvis begins is the lumbar region of the abdomen. The pelvis is composed of the bony pelvis, pelvic floor, pelvic cavity, and the perineum. The function of the pelvis is for structural support and stability.
Muscles
The muscles of the abdomen, in conjunction with the muscles of the back, provide posture and stability, helping the spine remain erect and adjust the position of the body. In the anterior aspect of the abdomen, the most superficial muscle is the external oblique muscle. Located deep to the external oblique is the internal oblique muscle, which is much thinner. The transversus abdominis muscle is the deepest, and the fibers run transversely. All of these muscles contribute to the linea alba at the midline. On either side of the midline, the rectus abdominis muscles are the vertical muscles that are divided by the linea alba. The pyramidalis is a muscle at the base of the pubic bone that also attaches to the linea alba
The muscles of the abdomen and back attach to the pelvis and work together with the muscles of the pelvis. Some pelvic muscles such as psoas major and iliacus help flex the trunk and thigh. The inferior aspect of the pelvic cavity is called the pelvic diaphragm.
The muscles that make up the pelvis diaphragm are the piriformis, coccygeus, iliococcygeus, pubococcygeus, and puborectalis.
