The bowel

The bowel is part of our digestive system which helps us break down the food we eat. It has two parts: the small bowel and the large bowel.

After we swallow food, it moves down the gullet (called the oesophagus) and into the stomach to be digested. The food then moves into the small bowel to be broken down further. This is where vitamins, minerals and nutrients are taken from the food and absorbed into the body.

From here, the food is then passed into the large bowel. The colon, rectum and anus make up the structure of the large bowel. The digested food first moves into the colon, where water is absorbed. The remaining waste product then moves into the rectum where it is stored until it can leave the body through the anus. The anus has a ring of muscle which helps us control when to open it and pass bowel motions.

What the bowel does

The bowel is part of our digestive system. It’s divided into two parts: the small bowel and the large bowel. The large bowel is made up of the colon, rectum and anus.

When food has been swallowed, it passes down the gullet (oesophagus) to the stomach, where digestion begins. From here, it enters the small bowel, where essential nutrients are taken into the body. The digested food then moves into the colon, where water is absorbed. The remaining waste matter (stool or faeces), is held in the rectum (back passage) until it’s ready to be passed from the body through the anus as a bowel motion (stool).

The anus is the opening at the very end of the large bowel. It contains a ring of muscle called the sphincter. This opens and closes giving you control over when you pass bowel movements.

The digestive system
The digestive system

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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 and 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.

The colon

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

The colon is divided into four sections:

Ascending colon

The first part of the colon starts at the bottom, right-hand side of the abdomen just after the small bowel and the appendix. This part goes up the right side of the abdomen.

Transverse colon

This second section goes across the abdomen from right to left.

Descending colon

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

Sigmoid colon

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

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.

Most rectal cancers start in the inner lining of the bowel and develop from small growths called polyps.

Back to Understanding rectal cancer

What is cancer?

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