The contents of your small intestine empty into your large intestine, which also goes by the terms "bowel" or "colon." As you can see, intestinal contents move through the ascending colon, across the transverse colon and down through the descending colon. As material moves through the various parts of the large intestine, water and salt are absorbed by the lining and the material is compacted into stool.
Typically, stool is moved into the rectum once or twice a day; pressure from this process stimulates the urge for a bowel movement. This process is not quite so simple in digestive disorders such as irritable bowel syndrome (IBS), in which problems with the motility, or movements of the muscles in the large intestine, result in symptoms such as diarrhea and constipation.
Essential Reading from Dr. Bolen, Your IBS Guide: