The word ‘bowel’ is a common term for the intestines, both small and large. However, bowel is also sometimes used to refer to the entire gastrointestinal tract from the esophagus to the anus but this technically incorrect. The intestines are the latter parts of the gastrointestinal tract. Here food is completely digested, nutrients absorbed, water and other electrolyte reabsorbed, waste material solidified and the feces stored until evacuation (defecation).
The Small Bowel
The small bowel is the small intestine made up of three parts – duodenum, jejunum and ileum. The duodenum lies immediately after the stomach and is the shortest part of the small intestine. Here partially digested food from the stomach is further digested due to the action of pancreatic enzymes, intestinal enzymes and bile. The duodenum then leads to the jejunum where further digestion occurs along with a significant portion of nutrient absorption. Finally the intestinal chyme, which is the digested food material mixed with water and mucus, is passed into the ileum. Very little digestion occurs in the ileum and absorption is the main priority.
The Large Bowel
The large bowel, or large intestine, starts at the cecum which is the junction between the small and large intestine. Here a sphincter known as the ileocecal valve controls in the inflow of intestinal chyme from the ileum into the large intestine. The major part of the large bowel is the colon. It is divided into four parts – ascending, transverse, descending and sigmoid colon. Here most of the water in the chyme is absorbed and in the process the liquid chyme is converted into a semi-solid and then solid mass. In this manner the feces are formed and stored in the latter parts of the colon. When the colon is full or due to the action of other defecation reflexes, the feces is passed into the rectum. Here it held for a short periods of time as the anal sphincters relax and colonic movements propel the feces into the anal canal. This is then passed out through the anus in the process known as defecation.