The first part of the small intestine is called the jejunum, and the latter part is referred to as the ileum. These are more or less arbitrary divisions, of value when explaining the various segments of the small bowel. Incidentally, the word small is used, for this relates to the actual diameter of this part of the intestinal system, rather than to its length. It is very long, but fairly narrow when compared to the next part, the “large bowel,” which is quite short in comparison, but wide in physical diameter.
The small bowel becomes a dilated area called the cecum. Attached to this is the appendix, a small wormlike structure that has no apparent function in humans, although it appears to be useful in digestion of certain foods in animals. The appendix is the source of a considerable amount of trouble, as most are aware. It is the site of frequent bouts of inflammation and represents one of the most common surgical emergencies for abdominal conditions. But more will be said of this troublesome organ later.
The cecum passes on to become the large bowel. The chief function of this organ is to absorb water from the food as it passes along the final stage of the intestinal system. It transforms the fluid mass to a relatively firm one. This is how the food (or what is left of it, by now almost completely devoid of nutritive value, for this has long since been absorbed by the small bowel) enters the final part of the bowel, the rectum. This is a short structure that holds the residue (now referred to as feces or stools) until a convenient time occurs when it may be expelled in a process called defecation.
The final process occurs when the valve at the far end of the system (called the anal sphincter) relaxes, and a bowel action takes place. In this manner, the fairly firm end product in the process of digestion is expelled. Besides the unwanted food residue, a large amount of waste material has been added to the bowel contents throughout its course, and this is also removed.