The Digestive Tract

Digestion is the process of converting food into energy and building blocks for the body’s functions. The process of digestion of food is very complicated involving several organs and many different functions. A brief overview of each organ and its basic function will be provided.

Digestion starts in the mouth as food is mechanically broken down by chewing. Saliva mixes with food to provide lubrication to ease passage further down into the esophagus. Material that is swallowed enters the esophagus which is a hollow muscular tube connecting the mouth and throat with the stomach. The walls of the esophagus, stomach and intestines contain several layers of muscle to mix food to propel material in a continuously downward manner. The esophagus is located in the middle of the chest and behind the heart just in front of the spine. Food enters the stomach, which is located in the upper part of the abdomen. The stomach has a larger internal cavity size and serves to secrete acid to break food down. The stomach has strong, muscular walls which mechanically break down solid food, such that when it leaves the stomach most material is in a liquid or near liquid state.

A sphincter muscle exists on either end of the stomach. At the top, where the esophagus and stomach meet, the lower esophageal sphincter (LES) stays closed except opening briefly when you swallow to allow material to pass into the stomach. It then closes to maintain a valve-(barrier) so that stomach acid and contents should be prevented from going back up into the esophagus. At the lower end of the stomach, the pyloric sphincter serves to control stomach contents leaving in an orderly fashion as they enter the small intestine.

Below the stomach is the small intestine which consists of three portions - the duodenum, the jejunum and the ileum. It is in the small intestine where food is absorbed after being broken down by enzymes into a size sufficiently small enough to pass through the lining cells of the small intestine into the bloodstream.

The liver is located in the right upper abdomen under the rib cage and serves several functions, such as cleansing the blood and synthesizing various proteins and clotting factors. The liver produces bile which aids in digesting fats. The bile leaves the liver into the bile duct and is then stored in the gallbladder. With eating, the gallbladder contracts releasing bile into the small intestine (duodenum) to mix with food.

The pancreas is located behind the stomach and empties its juices through the pancreatic duct into the small intestine in the same area as bile. The pancreatic juices are rich in enzymes, breakdown protein, fat and carbohydrates. The pancreas also makes the hormones, insulin and glucagon to control the level of sugar in the blood. As remaining material exits the small intestine, it goes through another valve - the ileocecal valve into the large intestine (also known as the colon). The primary function of the colon is to continue the process of absorbing water and to prepare the remaining residue for elimination as fecal material. The last sphincter in the system, the anus, serves to control appropriate timing of bowel movements.