The average American consumes 50,000 tons of food during their lifetime, but very few people know what happens to that food after it is swallowed.
Food is actually of little use to the body; it is the chemicals it contains, called nutrients, which are important. Nutrients are used to supply cells with energy and the raw materials needed to make things. As food passes through the digestive system, it separates nutrients from food, dissolves into individual molecules, and then absorbs them. The digestive system is composed of the following organs:
The listed organs are the parts of the alimentary canal, the 27 foot long tube also known as the food tube, through which food passes on its way out of the body.
The digestive process begins in the mouth where food is chewed into softer and smaller pieces. While the food is chewed, the salivary glands produce the saliva, mucus, and enzymes that begin the digestive process. The food, now called a bolus, is swallowed and then goes into the esophagus, a muscular tube that serves as a passageway to the stomach. Waves of peristalsis, or muscle contractions, push food to the stomach in just a few seconds.
In the stomach, food is mixed with gastric juices, hydrochloric acid (HCl), pepsin, and renin, to form chyme, a semiliquid. Peristaltic contractions continue to mash the food and mix it with the juices that begin to break down proteins in the food. Chyme is stored in the stomach for two to six hours and then moves on to the small intestine, the most important digestive organ.
The small intestine is between 18 to 21 feet long and is about one and a half inches wide. Bile and enzymes chemically change chyme again in to the individual molecules needed by cells. The walls of the small intestine are lined with millions of hair-like villi, covered with one layer of cells that have many pores, or openings, in them. Nutrients pass into these cells through the pores and then into the connected capillaries.
Whatever food left continues into the large intestine, or colon. in the colon, the only nutrient absorbed is the water added to the food in the other parts of the alimentary canal. Peristalsis continues to push the resulting unusable matter towards the rectum and anus where it mixes with bacteria to form feces. The bacteria, or intestinal flora, compose between 10% to 50% of the feces; the rest is mainly water, cellulose, fiber, mucus, and undigested nutrients.