An anal sphincter is a group of muscles at the end of the rectum that surrounds the anus and controls the release of stool, thereby maintaining continence. There are two sphincter muscles: one is internal and one is external. The external muscle helps maintain continence and keep stool in the rectum. If there is a loss of muscle control in the sphincter, incontinence may occur. The inner muscle is not under voluntary control but rather is controlled by the autonomic nervous system.
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Rectum Anatomy and Rectum Function. Differentiate Anus vs Rectum
At the level of the middle of the sacrum, the sigmoid colon loses its mesentery and gradually becomes the rectum, which, at the upper limit of the pelvic diaphragm, ends in the anal canal fig. The rectum, about 15 cm long, widens below as the ampulla, which is very distensible. Although variable in shape, the rectum follows the sacrococcygeal curve. At the anorectal junction, the gut curves backward and its concavity is held by the puborectal sling, which can be palpated per anum. The rectum presents three or more lateral curvatures, which correspond to transverse rectal folds in the interior of the gut. The rectum has neither mesentery nor haustra, and it has an almost complete outer longitudinal muscular coat rather than teniae.
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The anus is the opening at the end of your anal canal. The rectum sits between your colon and anus and acts as a holding chamber for stool. When pressure in your rectum becomes too great, the internal ring of muscle called the anal sphincter relaxes to allow stool to pass through your anal canal, the anus, and out of your body. The anus consists of glands, ducts, blood vessels, mucus, tissues, and nerve endings that can be highly sensitive to pain, irritation, and other sensations. Depending on the cause, a swollen anus can feel warm, cause sharp or burning pain especially after a bowel movement , and even produce bleeding and pus.
International Journal of Colorectal Disease. To investigate anal sphincter mechanics, anal pressure was measured in 14 normal males and 11 normal females using probes of 0. Resting pressure profiles on insertion and withdrawal did not differ significantly. Anteroposterior pressure differences could be explained by leverage of rigid probes against the anterior rectal wall.