The normal digestive system
The colon and rectum are parts of the digestive system, which is also called the
gastrointestinal (GI) system (see illustration). The first part of the digestive system (the
stomach and small intestine) processes food for energy while the last part (the colon and
rectum) absorbs fluid to form solid waste (fecal matter or stool) that then passes from the
body. To understand colorectal cancer, it helps to know something about the normal structure
of the digestive system and how it works.
After food is chewed and swallowed, it travels through the esophagus to the stomach. There
it is partly broken down and then sent to the small intestine, also known as the small bowel. It
is called small because it is narrower than the large intestine (colon and rectum), but actually
the small intestine is the longest segment of the digestive system ─ about 20 feet. The small
intestine continues breaking down the food and absorbs most of the nutrients.
The small intestine joins the large intestine (or large bowel) in the right lower abdomen. Most
of the large intestine is made up of the colon, a muscular tube about 5 feet long. The colon
absorbs water and salt from the food matter and serves as a storage place for waste matter.
The colon has 4 sections:
• The first section is called the ascending colon. It starts with a small pouch (the cecum)
where the small bowel attaches to the colon and extends upward on the right side of the
abdomen. The cecum is also where the appendix attaches to the colon.
• The second section is called the transverse colon since it goes across the body from the
right to the left side in the upper abdomen.