by Catherine Forse MD FRCPC
April 14, 2022
What is the anal canal?
The anal canal is the last part of the gastrointestinal tract. It connects the rectum to the anus. The anus is the external opening where fecal matter is released from the body.
What is the anatomy of the normal anal canal?
The anal canal is made up of 3 layers of tissue:
- Mucosa – The mucosa is the tissue that lines the inside of the anal canal. Within the mucosa of the anal canal, there are three zones: 1) colorectal zone, 2) transition zone and 3) squamous zone. The first is called the colorectal zone. It is made of epithelial cells that form glands. The second is the transition zone. In this zone, the epithelium changes from glands to specialized squamous cells. The transition point is called the dentate line. The third is the squamous zone. This zone is made entirely of squamous cells. The squamous zone connects with the skin at the very end of the anal canal.
- Submucosa – The submucosa contains many thick blood vessels that carry blood and lymphatic channels that carry waste and excess fluids away from the tissue.
- Muscle layer – This part of the anal canal is made up of different types of muscles which give the anal canal strength to store fecal matter and control defecation.