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An ampulla (from Latin bottle) is a cavity, or the dilated end of a duct, shaped like a Roman ampulla. [5] The rectum joins with the sigmoid colon at the level of S3, and joins with the anal canal as it passes through the pelvic floor muscles. [5] Unlike other portions of the colon, the rectum does not have distinct taeniae coli. [6]
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal.It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum.
Anatomy of the human anus. Frontal section. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum, passing through the pelvic floor. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation.
In humans, the anal canal is approximately 2.5 to 4 cm (0.98 to 1.57 in) long, from the anorectal junction to the anus. [2] [3] [4] It is directed downwards and backwards.. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior sl
It is an important anatomical landmark in humans, and forms the boundary between the anal canal and the rectum according to the anatomic definition. [1] Colorectal surgeons instead define the anal canal as the zone from the anal verge to the anorectal ring (palpable structure formed by the external anal sphincter and the puborectalis muscle). [1]
One is situated near the commencement of the rectum, on the right side. A second extends inward from the left side of the tube, opposite the middle of the sacrum. A third, the largest and most constant, projects backward from the forepart of the rectum, opposite the fundus of the urinary bladder.
The external anal sphincter is far more substantial than the internal anal sphincter. The proximal portion of external anal sphincter overlaps the internal anal sphincter (which terminates distally a little distance proximal to the anal orifice) superficially; where the two overlap, they are separated by the intervening conjoint longitudinal muscle.
The conjoint longitudinal muscle is a muscle layer in the wall of the anal canal between the internal anal sphincter (deep to CLM) and external anal sphincter (superficial to CLM).