The human digestive tract is an unique combination of internal and external surfaces. Though it is entirely inside the body, the digestive tract represents a hollow passage through the body that is more an exterior surface along which foreign matter (food) is selectively digested and absorbed. The human digestive system is an advanced form of gut that contains several distinct chambers for different parts of the digestion process.
The human digestive tract, also known as the gastrointestinal or GI tract, extends from the mouth on one end to the anus on the other. Along the way is the esophagus, stomach and small and large intestines. The total length of the digestive tract varies by person, but in an adult male can stretch from 20 to 40 feet. Several organs located alongside the GI tract, like the liver, gall bladder and pancreas, aid in the digestive process.
By far the longest part of the GI tract is the small intestine. Because it is thinner in width than the large intestine, it is called "small," but unraveled the small intestine is over 15 feet long in most people, and potentially over 30 feet. The small intestine is divided into three sections, the duodenum, the jejunum, and the ileum. In the duodenum, bile from the liver helps neutralize caustic stomach acids while pancreatic secretions continue the digestion process. Most absorption of nutrients takes place in the later sections of the small intestine.
The muscular tube connecting the mouth and the stomach is the esophagus. Unlike the small intestine, which is tightly curled up around itself, the esophagus is a more or less straight line from the mouth, down the middle of the chest, through the diaphragm to the stomach. It's about 10 inches (22 to 30 cm) in length. More than merely a passive tube, the muscular lining of the esophagus flexes to push food downward towards the stomach.
The large intestine is three to seven feet in length. It is mainly responsible for reabsorbing the water accompanying the undigested food that passes out of the small intestine. The remaining solid waste is prepared in the large intestine for elimination through the anal sphincter. The large intestine is divided into three sections, the ascending colon, transverse colon and descending colon based on the direction they run relative to the rest of the body.
There's a considerable amount of variability among different people in the length of time it take for food to pass completely through the digestive tract. And some foods move faster than others. On average, though, it takes a standard meal of mixed foods about 30 to 50 hours for the complete trip. It takes about four to five hours for the stomach to empty its contents into the small intestine. The transit through the colon is the slowest as the remaining solid material is dehydrated.