Understanding the Colon Function
Inside the abdominal cavity, the colon, or large intestine, begins with the cecum where it connects with the small intestine and continues to the rectum. Its length of about 5 feet is much less than that of the small intestine, but its diameter is much greater – about 2.5 inches.
The small intestine joins the large intestine at the cecum in the lower right abdomen, beneath the liver. At that point, it turns upward on the right side of the abdomen and is referred to as the ascending colon. At the top of the abdomen, the colon flexes and becomes the transverse colon — the portion which crosses the upper abdomen from right to left. At the left side, the colon flexes once again and becomes the descending colon. This section travels down the left side of the abdomen to an s-shaped area, or sigmoid colon, where it empties into the rectum. The ascending and descending parts of the colon are supported and fixed in place by the mesentery. The cecum, transverse and sigmoid colon parts are suspended by the mesentery from the rear abdominal wall.
When food is consumed, saliva in the mouth begins the digestive process. The food is moved by peristaltic waves down the esophagus to the stomach where many enzymes begin to break it down for absorption into the bloodstream. As the stomach contents are moved to the small intestine, the nutrients begin to be removed from the contents by villi, small finger-shaped appendages attached to the wall of the small intestine. These villi make it possible for nutrients to be sent into the bloodstream for use by the body.
By the time the contents of the small intestine are moved into the colon, it has become a watery mix of partially digested food, bile, and digestive juices, and measures about 3 pints in volume. A valve prevents the mix, called chyme, from re-entering the small intestine. As the chyme moves through the colon, its volume lessens to about 5 ounces. The colon is lined with mucosa, a layer of cells that makes it possible for nutrients to be absorbed into the bloodstream. The mucosa also acts as a lubricant in the movement of the chyme through the colon. It also prevents toxins from being absorbed into the body. The movement of the chyme through the colon is regulated by muscles and nerves, and takes from 12 to 14 hours.
The colon is made up of muscles, which run, lengthwise as well as circular. These muscles contract two or three times a day, making the churning and movement of its contents possible. Most of the churning occurs in the beginning area of the colon and more of the actual movement forward of the contents takes place in the descending and sigmoid portions.
One colon function is the removal of most of the moisture and the electrolytes or salts from the chyme, helping the fluid balance in the body. Electrolytes are essential or healthy heart function, among other processes. The colon also absorbs minerals and some vitamins from the chyme. These nutrients are reabsorbed into colic veins and then into the portal system of the bloodstream.
An important colon function is the production of various vitamins, such as Vitamin K and the B-Complex itamins, particularly B-12. There is some controversy among scientists about whether or not these vitamins are absorbed into the body to any great extent, causing some concern over the purpose of the colon’s manufacture of these vitamins. Some scientists believe they help protect the colon from cancer.
The colon contains millions of beneficial microorganisms. These bacteria break down most of the fiber in the feces, producing nourishment for the epithelial cells that line the colon. The colon needs the protection afforded by this fiber breakdown because of the toxins and harmful bacteria produced within it. Any fiber that is not digestible helps solidify the feces and aids its movement from the colon to the rectum.
The sigmoid colon also conducts the removal of water from the feces, further solidifying it. After eating, nerves and muscles signal the sigmoid colon to contract and empty into the rectum. Elimination is completed when the pelvic muscles and anal sphincters relax and allow the emptying of the rectum.