What is Colorectal Cancer

The digestive system is a long tube extending from the mouth at one end the anus (bottom) at the other end. The purpose of the digestive system is to break down food that is eaten so that energy and nutrients can be absorbed into the body. It also plays a role in absorption of water and the excretion of some waste products from the body.

The digestive system is divided into many parts along its length. Food which is taken into the mouth is chewed to help to break down the food. It is then swallowed and passes down the oesophagus to the stomach. In the stomach the food is broken down even more with the addition of digestive juices. After being in the stomach the food then passes into the small bowel where all the energy and nutrients are absorbed into the blood stream. Any non-absorbable contents of the small bowel pass into the large bowel. This is where water is absorbed into the body to make the contents of the bowel more solid. the solid contents is finally stored as a stool in the rectum until this is excreted out of the body through the anus when you go to the toilet.

Diagram of the digestive system.


The whole of the bowel is lined by epithelial calls which are a protective coating to the bowel wall. These cells are programmed to constantly replicate and produce new cells as old cells are eroded from the inner edge of the bowel. This replication is a very tightly regulated system, but sometimes damage to the regulation system can cause it can go wrong and cause more new cells to develop than are needed. If this happens then a small stalked outgrowth will develop from the bowel wall, this is called a polyp. Polyp's in themselves are harmless and will not cause any problems. However if they continue to grow they have the potential to develop into a cancer. This means that if any are seen at a colonoscopy then they will be removed.


If the polyp continues to grow then it can develop into a cancer. When this happens the cells are no longer acting as "normal" bowel cells but are replicating in an uncontrolled manner. Also the cells develop the ability to invade into other tissue such as other structures nearby, or distant organs through the blood or lymphatic systems. As well the cells develop immortality where they no longer will die; this is part of what makes treatment of cancer so difficult.

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