The small and large intestine, which have different anotomical features and functions, are the parts of the GI tract most affected by IBD.
The small intestine has three sections:
The small bowel is the longest but narrowest part of the intestine: about 7 meters long and 3 centimeters in diameter, in adults. It ends at the ileocecal valve, which joins the small intestine to the cecum (the upper part of the large bowel or colon).
The large intestine is shorter (about 1.5 meters in adults) but wider (about 6 cm) than the small intestine. It has five sections:
The three main functions of the GI tract are to:
Food travels down the esophagus and into the stomach, via the esophageal sphincter (valve). In the stomach, special enzymes and acids start a chemical breakdown of the food.
The partly digested food passes from the stomach into the small intestine, via the pyloric sphincter. As the food passes through the small intestine, digestion continues and most of its nutrients are absorbed into the bloodstream.
Finally, the food residue passes from the small intestine, via the ileocecal valve, into the large bowel (colon). There, water is absorbed before the food waste is evacuated (eliminated) as stool (feces), during bowel movements, via the rectum and anus.