Vasculature of the Pelvis

The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. The pelvic ring joints include the pubic symphysis anteriorly and the sacroiliac joints posteriorly. The hip bones are made up of 3 fused bones: the pubis, ischium, and ilium. The pelvic cavity houses various GI, urinary, and reproductive structures, which are supported by the muscles and connective tissue of the pelvic floor. The female pelvis, making accommodations for childbirth, is generally wider and larger than the male pelvis.

The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal incontinence can occur if this function is disturbed. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex) are essential for defecation to occur. The rich plexus of veins surrounding the anal canal can develop into hemorrhoids if dilated.