To better understand how weight loss surgery works, it is important to understand how your gastrointestinal tract functions. As the food you consume moves through the tract, various digestive juices and enzymes are introduced at specific stages that allow absorption of nutrients. Food material that is not absorbed is then prepared for elimination. A simplified description of the gastrointestinal tract appears below. Your doctor can provide a more detailed description to help you better understand how weight loss surgery works.

1. The esophagus is a long muscular tube, which moves food from the mouth to the stomach.


2. The abdomen contains all of the digestive organs.


3. The stomach, situated at the top of the abdomen, normally holds just over 3 pints (about 1500 ml) of food from a single meal. Here the food is mixed with an acid that is produced to assist in digestion. In the stomach, acid and other digestive juices are added to the ingested food to facilitate breakdown of complex proteins, fats and carbohydrates into small, more absorbable units.


4. A valve at the entrance to the stomach from the esophagus allows the food to enter while keeping the acid-laden food from "refluxing" back into the esophagus, causing damage and pain.


5. The pylorus is a small round muscle located at the outlet of the stomach and the entrance to the duodenum (the first section of the small intestine). It closes the stomach outlet while food is being digested into a smaller, more easily absorbed form. When food is properly digested, the pylorus opens and allows the contents of the stomach into the duodenum.


6. The small intestine is about 15 to 20 feet long (4.5 to 6 meters) and is where the majority of the absorption of the nutrients from food takes place. The small intestine is made up of three sections: the duodenum, the jejunum and the ileum.


7. The duodenum is the first section of the small intestine and is where the food is mixed with bile produced by the liver and with other juices from the pancreas. This is where much of the iron and calcium is absorbed.


8. The jejunum is the middle part of the small intestine extending from the duodenum to the ileum; it is responsible for digestion.


9. The last segment of the intestine, the ileum, is where the absorption of fat-soluble vitamins A, D, E and K and other nutrients are absorbed.


10. Another valve separates the small and large intestines to keep bacteria-laden colon contents from coming back into the small intestine.


11. In the large intestines, excess fluids are absorbed and a firm stool is formed. The colon may absorb protein, when necessary.