Canadian Cancer Society logo

Anal cancer

You are here: 

The anus

The anus is part of the digestive system. Stool leaves the body through the anus. It is the opening at the end of the large intestine after the rectum.

Diagram of the digestive system

Structure

The area around the anus is called the anal region. It is made up of the anal canal and the perianal skin.

Anal canal

The anal canal is a tube about 4 cm long. It connects the anus to the rectum, which is the holding area for stool. The junction between the rectum and anal canal is called the anorectal line.

The anal canal is surrounded by ring-like muscles called the anal sphincter (made up of the internal anal sphincter and the external anal sphincter). These muscles relax to let stool pass out of the body.

The anal canal is lined by a mucous membrane, which is a thin layer of moist tissue. It contains gland cells that make mucus (a thick, slippery fluid). This mucus helps stool move easily out of the body. The upper part of the anal canal contains folds of epitheliumepitheliumA thin layer of epithelial cells that makes up the outer surfaces of the body (the skin) and lines hollow organs, glands and all passages of the respiratory, digestive, reproductive and urinary systems. called anal columns. The lower part of the anal canal contains squamous cellssquamous cellsA type of epithelial cell that is thin, flat and looks like a fish scale.. The dentate line marks the place where the anal columns change to squamous cells. At the anus, the tissue starts to change from moist to dry and more like skin on the rest of the body.

Perianal skin

The perianal skin is the skin around the anus. The perianal skin is made up of squamous cells and is similar to skin found anywhere else on the body.

Diagram of the anal canal and structures

Diagram of the perianal area

Function

The anus is the end of the gastrointestinal (GI)gastrointestinal (GI)Referring to or having to do with the digestive organs, particularly the stomach, small intestine and large intestine. tract. When the rectum is full, your body feels the urge to have a bowel movement. The internal anal sphincter relaxes and pushes the stool from the rectum into the anal canal. Once the external anal sphincter relaxes, the stool is pushed out of the body through the anus.

Stories

Stella Gentil-Perret It’s a wonderful support system.

Read Stella's story

How can you stop cancer before it starts?

It's My Life! icon

Discover how your lifestyle choices can affect cancer risk and how you can take action with our interactive tool – It’s My Life!

Learn more