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Anatomy of the Colon and Rectum
The colon is the end of the intestinal tract. It is 8 to 12 feet
in length. It begins at the junction of the small bowel called the
ileocecal valve, goes up along the right side of the abdomen, across
the top and down the left side of the abdomen. These are respectively
termed the ascending, transverse and descending sections of the
colon. The lower part of the colon is called the sigmoid, and the
sigmoid joins the rectum about 15 centimeters (6 inches) from the
anus. There is no difference between the colon and rectum and these
are just terms to designate an area of the large intestine. The
rectum is 15 centimeters in length and is that area just above the
anus.
The anus is a muscle that closes the colon. It is this outlet obstruction
that allows us to be continent. We define continence as the ability
to defer defecation until a socially convenient time. This says
nothing about the number of bowel movements, the quality of the
bowel movements (liquid or solid), but this definition does point
out that the bowel habits should not have a significant influence
on the quality of life of the individual. Our ability to control
our bowels until a socially convenient time is controlled by the
sphincter muscles that act as a plug and the rectum, which acts
as a storage area. If the rectum is inflamed or scarred, then it
does not work properly as a storage vessel. If either the anal muscle
or the rectum is not working properly, control of the bowels is
difficult. After surgical removal of the rectum, bowels movements
will, at least temporarily, be more frequent and urgent. This is
because the storage area is not working properly. It will recover
and adjust after several weeks.
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