The Colon: Another Name for Large Intestine

Understanding the Role of the Large Intestine

Large Intestine
Large Intestine. Wikimedia Commons

The colon, which is another name for the large intestine, is an important part of the digestive system. The large intestine plays a major role in the gastrointestinal (GI) tract, including:

  • reabsorbing water and maintaining the body's balance of fluids
  • absorbing vitamins
  • processing undigested food material such as fiber
  • storing waste before elimination

Why Is It Called the Large Intestine?

This organ is called the large intestine because of the diameter (width) of the intestine; it is much wider than the small intestine, but also much shorter.

The large intestine is approximately six feet in length, while the small intestine is much longer, at approximately 21 feet. The last six inches or so of the large intestine are called the rectum and the anal canal.

What Is the Colon Made Up Of?

The colon extends from the cecum (where the small intestine meets the large intestine) to the anus (where waste exits the body), and comprises four main regions:

  • Ascending colon: begins at the cecum at the bottom right side of the abdomen and ascends (goes upwards) 
  • Transverse colon: runs across the abdomen from right to left
  • Descending colon: descends (goes downward) along the left side of the abdomen
  • Sigmoid colon: the S-shaped connection between the last part of the colon and the rectum, located on the bottom left side of the abdomen

Just like the other parts of the GI tract, the colon is comprised of four layers of tissue:

  • Mucosa: This is the innermost layer and is made of simple columnar epithelial tissue, making it smooth (compared to the small intestine, which contains villi, small fingerlike protrusions). Many glands secrete mucus into the interior lumen of the large intestine, which lubricates its surface and protects it from abrasive food particles.
  • Submucosa: The mucosa is surrounded by the submucosa, which is a layer of blood vessels, nerves and connective tissue that supports the other layers of the large intestine. 
  • Muscularis: The submucosa is surrounded by the muscularis, which contains many layers of visceral muscle cells that contract and move waste product through the large intestine in a process known as peristalsis.
  • Serosa: The outermost layer, known as the serosa, is a thin layer of simple squamous epithelial tissue. The serosa secretes a watery fluid that provides lubrication for the colon's surface that protects it from damage due to contact with other abdominal organs as well as the muslces and bones of the lower torso that surround it. 

How Does the Colon Contribute to Digestion?

As chyme, a slurry of digested food, passes from the small intestine into the colon through the ileocecal sphincter and the cecum, it mixes with beneficial bacteria from the colon. It then moves through the four regions of the colon over the course of several hours as a result of peristalsis. In some cases, this process can become much faster by stronger waves of peristalsis that follow a large meal.

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