How the Large Intestine Works

Through the ileo-cecal valve, chyme is passed into the cecum from the small intestine.  At this stage, the chyme consists of undigested or undigestible food substances, secretions from the liver, pancreas, small bowel and water.  In the cecum, the water is mostly removed, reducing the chyme to a semi-solid consistency which we call feces.

To provide lubrication for the passage of the feces (aren’t you glad?), numerous cells line the walls of the bowel and secrete a mucus substance for ease of elimination.  As a result of haustral churning, a constant sloshing effect finishes the digestive process of the chyme.  Which kind of explains why our stomachs and intestines make such noises audible to our ears sometimes.

Under mass peristalsis, the feces are pushed toward the rectum and anus where they are eventually eliminated.  This movement is caused by the presence of food in the stomach and this activity empties the cecum and makes it ready to receive new chyme from the small intestine.

Under normal circumstances, there is very little bacterial activity in the small intestine.  The large intestine, however, swarms with billions of these microscopic organisms – and for good reason.

Bacterial action in the large intestine is a major contributor to synthesize valuable nutrients by digesting portions of the fecal mass.  Among others, vitamin K and portions of  B complex are produced.  This aspect of digestion is not completely understood and is undergoing further study. 

Any remaining proteins are broken down by the bacteria into simpler substances.  Byproducts of bacterial activity are numerous, such as indole, skatole, hydrogen sulfide, fatty acids, methane gas and carbon dioxide.  Some of these substances are very smelly and toxic, hence you’ll notice smelly feces at times.