Describe what happens to unabsorbed food after leaving the small intestine. Describe the structure and function of the large intestine. What makes up more than half the dry weight of feces; where are feces stored until elimination?
From the small intestine, the unabsorbed food passes into the large intestine, or colon, at the lower right-hand portion of the abdominal cavity. Near the juncture of the small and large intestines, a blind sac, or caecum, tipped by the appendix projects off the large intestine. Both the caecum and appendix are functionally unimportant in humans. The large intestine has three segments: the ascending colon, which runs up the right side of the abdominal cavity, the transverse colon, which runs across the top of the abdominal cavity, and the descending colon, which runs down the left side of the abdominal cavity. The large intestine re absorbs the large quantities of water used to secrete enzymes into the upper portions of the digestive tract. In addition, the large intestine excretes salts, such as calcium and iron, when the salts' blood concentrations are too high. The large numbers of bacteria that inhabit the large intestine feed on the undigested food and make up half of the dry weight of feces. The rectum is the last segment of the large intestine. It stores feces until defecation when the feces are eliminated from the rectum through the anus.
