Anal Injury Anatomy
To better understand anal injury, it helps to understand the anatomy of the colon, rectum and anus.
The large intestine is also known as the colon. It is the last portion of the intestine. The colon has several parts, including:
- Ascending colon: the first section after the small intestine, located on the right side
- Transverse colon: sits horizontally across the upper abdomen
- Descending colon: located on the left side of the abdomen
- Sigmoid: a short, S-shaped section above the rectum
- Rectum: the lowest internal part of the colon
The anus is the opening on the gastrointestinal tract, where the stool exits. The anus marks the transition from the lining of the gastrointestinal tract to the external skin. The anal canal is a tube, 1-2 inches long that leads to the anus. The anal canal is surrounded by circular muscles, called sphincters, and blood vessels. The sphincters control defecation.
- Abou-Zeid AA. Preliminary experience in management of fecal incontinence caused by internal anal sphincter injury. Dis Colon Rectum. 2000 Feb;43(2):198-202. 
- Ameh EA. Anal injury and fissure-in-ano from sexual abuse in children. Ann Trop Paediatr. 2001 Sep;21(3):273-5. 
- Nichols CM, Gill EJ, Nguyen T, Barber MD, Hurt WG. Anal sphincter injury in women with pelvic floor disorders. Obstet Gynecol. 2004 Oct;104(4):690-6.