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.
46 How Our Body Works 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 24 hours a day, 7 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.
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