The colon is an organ and a part of the gastrointestinal tract. Other parts of the gastrointestinal tract include the mouth, esophagus, stomach, small bowel, rectum, and anal canal. The colon is a long hollow tube that starts at the small bowel and ends at the anal canal. Together, the colon, rectum, and anal canal form the large intestine.
The colon has two main functions. The first is to move stool (digested food) from the small bowel out of the body. The second is to remove water from the stool and return it to the body.
The colon is divided into five sections called the cecum, ascending colon (right colon), transverse colon, descending colon (left colon), and sigmoid colon. The inside of the colon is covered by specialized goblet cells that produce a substance called mucin. These cells iconnect together to form long straight glands. The bottom of the glands in the colon are called crypts.
The glands are in a thin layer of tissue called mucosa. Below the mucosa are layers of connective tissue and muscle that help the colon function normally. The outside surface of the colon is covered by fat and a thin layer of tissue called serosa.
The most common type of colon cancer is called adenocarcinoma. It starts from cells normally found on the inside surface of the colon. Other less common types of colon cancer are gastrointestinal stromal tumour and well differentiated neuroendocrine tumour.