What happens to food after it leaves the stomach?
The mixture of partially digested food drenched in acidic stomach juice is slowly sent into the small intestine. This portion of our digestive tract is the location of the majority of digestive enzyme activity and the absorption of nutrients. The wall of the small intestine presents a very sophisticated pattern of folds and projections. This design allows the small intestine to have an absorptive surface approximating the size of a tennis court. This allows for very efficient absorption.
When the food mixture is spurted into the small intestine from the stomach, it hardly resembles what we ate. Yet most of the nutrients still need further digestion to reach their absorbable state. First, bicarbonate produced by the pancreas enters the small intestine and neutralizes the acidic food mixture draining from our stomach. Then digestive enzymes that are also produced by our pancreas and bile from the gallbladder and liver make their way to the small intestine as well. These factors, along with digestive enzymes produced by the cells that line the small intestine, will complete digestion.
What is bile?
Bile is made up of several substances, the most outstanding being bile acids (bile salts). During digestion, the small intestine is a watery place to be. Along with the water entering our digestive tract in foods and beverages, water is also the basis of digestive juices. Water-insoluble substances in our diet, such as fats, cholesterol, and fat-soluble vitamins, will clump together into droplets in the small intestine. This would decrease their digestibility and absorption. This is where bile comes in. Bile acts as an emulsifier or detergent interacting with lipid droplets so that many smaller lipid droplets result instead of fewer larger ones. The advantage to creating many smaller lipid droplets is that more contact occurs between lipids and lipid-digesting enzymes. If bile were absent, as in certain disorders, lipids would stay as larger droplets in the small intestine and for the most part remain undigested and unabsorbed and end up in the feces.
Bile is produced by the liver and oozes in the direction of the small intestine twenty-four hours a day, seven days a week. The liver is connected to the small intestine via a series of tubes or ducts. During periods of time in between meals, some of the bile drains into the gallbladder, where it is stored. Then during a meal the gallbladder squeezes the bile out and it heads to the small intestine. This allows for more bile to be present in the small intestine during digestion.
What is the colon?
By the time the digestive mixture reaches the large intestine or colon most of the nutrients have been absorbed. Although some water and electrolytes will be absorbed in the colon, its primary responsibility is to form the feces that will eventually leave the digestive tract. The colon is also home to a rich bacteria colony—as many as 400 different species of bacteria may be found. These bacteria provide some benefit to the body as they make some vitamins and fatty acids that can help nourish the body. Research is underway in an effort to better understand the relationship between the colon’s bacteria and human health.
What is the composition of feces?
Human feces is a combination of water, bacteria, parts of cells that line the digestive tract, and undigested food components, such as fibers. The coloring of feces is attributable to several of the substances that are removed from the body in the feces. For instance, when the body breaks down hemoglobin, coloring pigments are produced. These substances become part of bile, which empties into the digestive tract. These add color to the feces
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