Anatomy of the Colon

This article outlines the anatomy of the colon, also called the “large intestine.” The colon is part of part of the digestive system which starts at the mouth and ends at the anus.

Where does the colon fit in?

In a nutshell, food travels from our mouths to the stomach where it is broken down into a watery soup-like substance called “chyme.” It then enters the small intestine which despite its name is an astonishing 20 feet long.

After traveling through the small intestine, the chyme passes into the large intestine – the colon. About three pints (1.5 liters) of fluid enter the colon from the small intestine each day.

Compared to the small intestine the colon is relatively short, measuring “only” around five feet in length. However is has a diameter of 2.5 inches - twice that of the small intestine. Hence it is called the “large intestine.”

Although not part of the anatomy of the colon, the colon is populated by hundreds of varieties of bacteria, also referred to as “microbial bacteria” or “intestinal flora” which chemically break down the chyme.

A remarkable aspect of the anatomy of the colon is its water absorption properties. The colon walls are capable of absorbing up to ten pints (4.5 liters) of water a day – far more than enters the colon.

As a result of water absorption, the watery chyme gradually thickens as it progresses along the colon. By the time it passes into the lower or “descending” part of the colon it has thickened into stools.

The walls of the colon are ringed with band-like muscles. The colon walls are thinner and weaker between these muscles and vulnerable to damage and infection. Two or three times a day nerve, hormone and electrical activity cause these muscles to contract in a wave-like manner, called “peristalsis.”

Peristalsis shunts the waste in the colon back and forth but mostly down towards the anus. This movement of waste through the colon is known as “motility.” Thus people with constipation have “poor motility.”

The colon produces and stores about 3 to 8 ounces of stool a day which is eventually delivered to the rectum ready to be excreted through the anus.

When all is well, the entire process of digestion takes 12 to 24 hours and results in 2 to 3 bowel movements a day. However, colon problems are common, ranging from constipation and cramps to colon cancer (colorectal cancer).

Most colon problems can be prevented by taking steps to eliminate the key causes of colon problems and promote healthy colon function, including a colon-friendly diet, colon cleansing, drinking more water and taking more exercise.