The digestive system and colon are related in that the colon is the final portion of the digestive tract. Also referred to as the large intestine, the colon has four sections distinguished by their direction: the ascending colon, transverse colon, descending colon, and sigmoid colon. Both the digestive system and colon function to move partially digested food through the body. The colon additionally functions to pull salt, water, potassium, and some vitamins from the remaining undigested mass before that mass is removed from the body as stool.
Extending from the mouth to the rectum, the digestive system encompasses the organs that break down food into its macronutrient components — carbohydrates, fat, and protein — as well as its micronutrient components — vitamins, minerals, and water. It also includes those organs that contribute to the absorption of said nutrients so that they can be converted into energy, as well as those that transport any unused portion of the food out of the body. Digestion begins in the mouth with the physical breakdown of food and continues as the food is moved along the esophagus and into the stomach, where much of the chemical breakdown of food occurs. The bolus, or partially digested mass, then reaches the small intestine, where much of its macronutrient content will be absorbed.
Beyond the small intestine is the colon, the largest organ of the digestive system. Approximately 6 feet (1.8 meters) in length, it consists of the ascending colon, which directs upward from the small intestine; the transverse colon, which crosses the abdominopelvic cavity horizontally; the descending colon, which takes a 90 degree turn downward; and the sigmoid colon, which curves like the letter S. It ends where the sigmoid meets the rectum.
The digestive system and colon both transport food through the body, but unlike the previous organs, the colon handles only the extraction of micronutrients: minerals, vitamins, and water. These include sodium, magnesium, and potassium, which are significant to muscle function and also are referred to as electrolytes. Also absorbed here are the fat-soluble vitamins A, D, E, and K. These are not removed in large quantities, as most of the nutrients that the body requires have already been absorbed.
Another functional difference between the preceding organs of the digestive system and colon is the presence of fermenting bacteria in the colon. Known as flora, they reside permanently in the large intestine and enjoy a symbiotic relationship. The flora feed off a small amount of the fiber in the undigested material, most of which cannot be broken down by the digestive system and colon and therefore is eliminated in stool. In return, they release byproducts from this fiber breakdown that contribute to the health of the cells lining the walls of the colon.