The anus

The anus is the opening at the end of the large bowel where we pass stools (bowel motions) out of the body. The bowel (colon and rectum) and anus are part of the digestive system.

The digestive system
The digestive system

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Food passes down the gullet (oesophagus) into the stomach to be digested. It then moves into the small bowel, where important nutrients are removed from it and absorbed into the body.

Digested food moves into the large bowel, where water is absorbed. The waste product (stools) remains in the back passage (rectum) until it can be passed out of the body through the anus.

The anal canal is about 3 to 4cm (1 to 1½in) long. It connects the anus to the rectum. The area where the anus opens at the lower end is called the anal margin or anal verge. 

The anus also has a ring of muscle called the external sphincter. This muscle helps to control when you pass bowel motions.

A cross-section of the anal canal
A cross-section of the anal canal

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The walls of the anal canal are lined with cells called squamous cells. Nearly all anal cancers develop in these cells. We have more information about different types of anal cancer.

Where the anal canal meets the rectum (transitional zone), the walls are lined with squamous cells and glandular cells. Glandular cells make mucus that helps the bowel motions to pass through the anus.

Back to Understanding anal cancer

What is cancer?

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

The lymphatic system

The lymphatic system helps to protect us from infection and includes lymph nodes (glands). There are lymph nodes near the anus.

Types of anal cancer

There are different types of anal cancer. The most common type of anal cancer is squamous cell carcinoma.