About Colorectal Cancer

The Digestive System

The digestive system is made up of the digestive tract – a series of hollow organs joined in a long, twisting tube from the mouth to the anus – and other organs that help the body break down and absorb food.

The colon and rectum are parts of the digestive system, which is also called the gastrointestinal (GI) system. The first part of the digestive system 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. After food is chewed and swallowed, it travels through the esophagus to the stomach. There is a partly broken down and then sent to the small intestine, also known as the small bowel. Small describes the diameter of the intestine, which is narrower than that of the large bowel (colon and rectum). 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 bowel joins the colon in the right lower abdomen. The colon (also called the large bowel or large intestine) is a muscular tube about five feet long. The colon absorbs water and salt from the food matter and serves as a storage place for waste matter.

The colon has four 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.
  • The third section is called the descending colon, and it continues downward on the left side.
  • The fourth and last section is known as the sigmoid colon because of its "S" or "sigmoid" shape.

The waster matter that is left after going through the colon is known as feces or stool. It goes into the rectum, the final six inches of the digestive system, where it is stored until it passes out of the body through the anus.

The wall of the colon and rectum has several layers of tissues. Colorectal cancer starts in the inner layer and can grow through some of all of the other layers. The stage (extent of spread) of a cancer depends to a great degree on how deep the cancer goes into these layers.

Abnormal growths in the colon or rectum

Cancer that starts in these different areas may cause different symptoms. But colon cancer and rectal cancer have many things in common. In most cases, colorectal cancers develop slowly over many years. We now know that most of these cancer begin as a polyp (a growth of tissue that starts in the living and grown into the center of the colon or rectum). This tissue may or may not be cancer. A type of polyp known as an adenoma can become cancer. Removing a polyp early may keep it from becoming cancer.

Over 95% of colon and rectal cancers are adenocarcinomas. This is cancer that starts in the cells that line the inside of the colon and rectum. There are some other, more rare, types of tumors of the colon and rectum.


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