Rectal ampulla

The rectal ampulla is the dilated terminal part of the rectum located immediately above the anal canal. It represents the widest portion of the rectum and serves as a temporary reservoir for faecal material prior to defecation. The ampulla is normally empty but expands as faeces enter from the sigmoid colon, allowing storage without a marked increase in intrarectal pressure.

Anatomical relations

• The rectal ampulla occupies the lower third of the rectum, extending from approximately the level of the middle rectal fold to the anorectal junction.

• Posteriorly, it is related to the sacrum and coccyx,

• Its anterior relations differ between the sexes. In males, it is related to the base of the urinary bladder, seminal vesicles, vas deferens, and prostate gland. In females, it is related to the vagina and cervix, with the rectouterine pouch (pouch of Douglas) intervening superiorly.

Functional correlate

The wall of the rectal ampulla is highly distensible, allowing it to accommodate varying volumes of faecal material. Distension of the ampulla stimulates stretch receptors within the rectal wall, initiating the defecation reflex. This reflex results in relaxation of the internal anal sphincter and generates the conscious sensation of the need to defecate.