Colon (large intestine)à
The colon is a 6-foot long muscular tube that connects the small
intestine to the rectum. The large intestine is made up of the
cecum,
the ascending (right) colon, the transverse (across) colon, the
descending (left) colon, and the sigmoid colon, which connects to
the
rectum. The appendix is a small tube attached to the cecum. The
large intestine is a highly specialized organ that is responsible
for
processing waste so that emptying the bowels is easy and convenient.
Stool, or waste left over from the digestive process, is passed
through the colon by means of peristalsis, first in a liquid state and
ultimately in a solid form. As
stool passes through the colon, water is removed. Stool is stored
in
the sigmoid (S-shaped) colon until a "mass movement"
empties it
into the rectum once or twice a day. It normally takes about 36
hours
for stool to get through the colon. The stool itself is mostly food
debris and bacteria. These bacteria perform several useful functions,
such as synthesizing various vitamins, processing waste products
and
food particles, and protecting against harmful bacteria. When the
descending colon becomes full of stool, or feces, it empties its
contents into the rectum to begin the process of elimination.
Rectumà
The rectum (Latin for
"straight") is an 8-inch chamber that connects
the colon to the anus. It is the
rectum's job to receive stool from the
colon, to let the person know that there
is stool to be evacuated, and
to hold the stool until evacuation
happens. When anything (gas or
stool) comes into the rectum, sensors
send a message to the brain.
The brain then decides if the rectal contents
can be released or not.
If they can, the sphincters relax and the
rectum contracts, disposing
its contents. If the contents cannot be
disposed, the sphincter
contracts and the rectum accommodates
so that the sensation
temporarily goes away.
Anusà
The anus is the last part of the digestive
tract. It is a 2-inch long
canal consisting of the pelvic floor
muscles and the two anal
sphincters (internal and external). The
lining of the upper anus is
specialized to detect rectal contents.
It lets you know whether the
contents are liquid, gas, or solid. The
anus is surrounded by sphincter
muscles that are important in allowing
control of stool. The pelvic floor
muscle creates an angle between the
rectum and the anus that stops
stool from coming out when it is not
supposed to. The internal
sphincter is always tight, except when
stool enters the rectum. It
keeps us continent when we are asleep
or otherwise unaware of the
presence of stool. When we get an urge
to go to the bathroom, we
rely on our external sphincter to hold
the stool until reaching a toilet,
where it then relaxes to release the
contents.
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