Transverse Section - Pelvis

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Module Name: abd1820
Module Title: Transverse Section - Pelvis
Image Info: Tansverse Section through the abdomen/pelvis; Visible Human Project.
Created by: Lynn Bry
Date: January 12th, 1997


Key points: iliopsoas muscle | colon | rectus abdominus | gluteal muscles | mesentary | pelvis | sacrum |

Introduction: This section illustrates structures found within the pelvis of a man. Structures shown include the following: posteriorly - gluteus maximus muscle, sacrum and iliac bones; anteriorly - the large intestine, iliopsoas muscle and rectus abdominus muscle. The bladder lies below this section.


abdominal_wall_muscles: At this level little can be seen of the muscles of the anterior abdominal wall, aside from the centrally located rectus abdominus Of the three remaining muscles, the external oblique muscle is the most external of the three. It's muscle fibers run perpendicularly to those of the underlying internal oblique muscle. These two muscles help compress the abodomen when straining, and flex the torso when twisting or bending from side to side. The fibers of the third muscle, the transversus abdominus run horizontally. Sit-ups exercise all three muscles.

colon: The large intestine (colon) is distinguished from the small intestine by its larger diameter, both in size, and in terms of the greater diamter of the lumen. Colonic haustra or individual segments of the sigmoid colon can be seen. Three layers of smooth muscle make up the wall of the colon and serve to move lumenal contents through the bowel in a continuous process referred to as peristalsis.

fatty_tissue: The subcutaneious fat and fashia can be seen beneath the surface of the skin. The loose fashia is filled with body fat and is one of the body's main forms of insulation. The fat may also be metabolized and used for energy during periods of starvation.

gluteal_muscles: The gluteus maximus is one of the larger muscles in the body. It forms the muscular area under the buttocks. The muscle originates from the sacrum and inserts on the posterior aspect of the femur (gluteal tuberosity). Behind it lies the gluteus medius and gluteus minimus muscles which are also visible in this section. These muscles help abduct (kick your leg to the side), rotate, and extend (kick your leg behind you) the hip joint. The gluteal muscles also play an important role maintaining the body's posture while standing. Without them we would be unable to stand, walk or run.

iliopsoas_muscle: The iliopsoas muscle is a primary flexor of the hip (bringing the knees into the chest). The psoas major muscles originate on the lower region of the backbone, run across the anterior region of the pelvis (as shown here) and insert onto the femur - the long bone of the leg.

mesentary: Much of the fatty tissue within the pelvic cavity is associated with the mesentaries. The mesentaries are sheets of fatty and connective tissue attached to the intestines and internal organs of the abdomen. They result from a complex folding of the lining of the abdomen (the peritoneum) during development. They contain the blood vessels and lymphatics that supply these organs. Many mesenteric vessels can be seen in this section. Though appearing as a dense area of fat, note the thin yellow lines that separate individual folds of mesentary.

multifidus: The multifidus muscle consists of a series of muscles which run from the transverse processes or 'side arms' of vertebrae to the spine, or part of the vertebra that projects posteriorly, above. Some muscles extend for 3-4 vertebrae, or from one vertebra to another. These muscles rotate the spine (do the twist).

pelvis: Four bones (2 'hip' bones - one on each side + sacrum + coccyx) make up the 'pelvis' - the posterior region is made up of the sacrum and coccyx which reside at the end of the spine. The hip bones themselves are divided into three parts - the ilium, ischium and pubis. The iliac crest of the ilium forms the 'hips'; the ischium forms the bony part of the 'rump' and the two pubic bones meet in a catilagenous connection in the groin to form the pubic symphysis. This section cuts through the ilium. The sacrum can be seen in the middle connecting the two iliac crests.

rectus_abdominus: The rectus abdominus muscle comprises the central region of the anterior abdominal wall. (It receives heavy usage during sit-ups.) The muscle is made of many segments, which produces the 'tortise shell' appearance of the abdomen in body builders. A tendinous sheath covers the rectus abdominus. This sheath is made of the aponeuroses of the three adjacent muscles on either side of the antierior abodomen - the external oblique, internal oblique, and transversus abdominus muscles. A small triangle of these muscles can be seen on either side of the rectus abdominus.

sacrum: The sacrum consists of five vertebrae fused into a single bone. This bone makes up part of the pelvic girdle and plays an important role in transmitting the weight of the body to the hip joints.

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