The bowel

The bowel is part of the digestive system. It is divided into two parts: 

  • the small bowel
  • the large bowel.

The large bowel is made up of the colon, rectum and anus.

The bowel
The bowel

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When you swallow food, it passes down the gullet (oesophagus) to the stomach, where digestion begins.

It then enters the small bowel, where nutrients and minerals from food are absorbed. The digested food then moves into the colon, where water is absorbed. The remaining waste matter (stool or poo) is held in the rectum (back passage). It stays here until it is ready to be passed out of the body through the anus.

The colon

The colon is divided into four sections (see diagram above):

Ascending colon

The first part of the colon is joined to the small bowel and goes up the right side of the abdomen.

Transverse colon

The second section goes across the abdomen from your right to your left side.

Descending colon

The third section goes down the left-hand side of your abdomen.

Sigmoid colon

The final part of the colon is an ‘S’ shape bend that joins on to the rectum.

The lining of the colon is made up of layers of body tissue. Most colon cancers start in the inner lining of the bowel and develop from small growths called polyps.

The rectum

The rectum links the colon to the anus. It is about 15cm (6 inches) long.

To help describe where a cancer is, doctors divide the rectum into thirds: upper, middle and lower. The upper third is the section directly after the sigmoid colon (see diagram above). The lower third is where the large bowel joins the anus. The middle third is in between.

The lining of the rectum is made up of layers of body tissue. Most rectal cancers start in the inner lining of the bowel and develop from small growths called polyps.

The small bowel

The small bowel is part of the digestive system and extends between the stomach and the large bowel (or colon). The small bowel is divided into three main parts:

  • the duodenum
  • the jejunum
  • the ileum.

The small bowel folds many times to fit inside your abdomen and is around five metres (16 feet) long. It is responsible for the breakdown of food, which allows vitamins, minerals and nutrients to be absorbed into the body.

Back to Understanding colon cancer

What is cancer?

There are more than 200 different kinds of cancer, each with its own name and treatment.