Colon Cancer Overview. The human colon, or large intestine, is a muscular, tube-shaped organ measuring about 4 feet long. It extends from the end of your small bowel to your anus. Typically the first or right portion of the colon which is called the ascending colon moves up from the lower right portion of the abdomen. The next portion, or transverse colon, moves across from the right to the left side of the upper abdomen.