Anus

The anus is the terminal opening of the digestive tract, where feces leave the body. Its sphincter muscles help control defecation and maintain continence.

Anal sphincter: Muscles surrounding the anal canal that regulate the passage of feces and help maintain continence. The internal and external sphincters close the opening and relax during defecation.
Large intestine: The part of the digestive tract that absorbs water and forms feces. Its final section supplies the material that passes through the anus.
Hemorrhoid: An enlarged or swollen vascular cushion in the anal canal or around the anus. Hemorrhoids can cause anal bleeding, discomfort, or protrusion.
Urethra: The passage that carries urine from the bladder out of the body. It is a separate outlet, positioned near but distinct from the anus.
Proctodeum: An embryonic ectodermal depression that contributes to the lower anal canal. Its tissue forms the external portion of the anal canal and opening.
Defecation: The bodily process of expelling feces through the anus. It coordinates rectal pressure, pelvic-floor relaxation, and anal opening.
Pelvic floor: A group of muscles and connective tissues that supports pelvic organs and helps control elimination. Its muscles support anorectal alignment and assist continence.
Anal fissure: A tear in the lining of the anal canal, often causing pain during defecation. The tear can make passage of stool sharply painful.
Vagina: An elastic muscular canal connecting the uterus to the external genital tract. In people with this anatomy, it is another distinct opening near the anus.
Hindgut: The embryonic region that forms the distal digestive tract, including the upper anal canal. It contributes the internal portion above the pectinate line.

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