Understanding the gastrointestinal tract


To better understand how bariatric surgery works, it’s important to understand what happens during the normal digestive process.


The following visual aid shows how food that’s eaten moves through the GI tract, the stages where various digestive juices and enzymes are introduced to allow absorption of nutrients, and where food material that is not absorbed is prepared for elimination.


For more information, ask your doctor.



The digestive system

  • The esophagus is a long, muscular tube that moves food from the mouth to the stomach.
  • The abdomen contains all of the digestive organs.
  • 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.
  • 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.
  • The pylorus is a small, round muscle located at the outlet of the stomach and the entrance to the small intestine. It closes the stomach outlet while food is being digested into a more easily absorbed form. When food is properly digested, the pylorus opens and allows the contents of the stomach into the first portion of the small intestine.
  • The small intestine is about 15 to 20 feet long and is where the majority of absorption of the nutrients from food takes place. The small intestine is made up of three sections: the duodenum, the jejunum, and the ileum.
  • 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.
  • The jejunum is the middle part of the small intestine extending from the duodenum to the ileum; it is responsible for absorption of nutrients.
  • The last segment of the intestine, the ileum, is where the absorption of fat-soluble vitamins A, D, E, and K
    and other nutrients occurs.
  • Another valve separates the small and large intestines to keep bacteria-laden colon contents from flowing back into the small intestine.
  • In the large intestine, protein and excess fluids are absorbed and a firm stool is formed.