Rectum Scholarly Peer-review Journal

   The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction, the end of the sigmoid colon, at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used. In humans, the rectum is followed by the anal canal which is about 4 centimetres (1.6 in) long, before the gastrointestinal tract terminates at the anal verge. The word rectum comes from the Latin rectum intestinum, meaning straight intestine. The blood supply of the rectum changes between the top and bottom portions. The top two thirds is supplied by the superior rectal artery. The lower third is supplied by the middle and inferior rectal arteries.   The superior rectal artery is a single artery that is a continuation of the inferior mesenteric artery, when it crosses the pelvic brim.[8] It enters the mesorectum at the level of S3, and then splits into two branches, which run at the lateral back part of the rectum, and then the sides of the rectum. These then end in branches in the submucosa, which join with (anastamose) with branches of the middle and inferior rectal arteries. The microanatomy of the wall of the rectum is similar to the rest of the gastrointestinal tract; namely, that it possesses a mucosa with a lining of a single layer of column-shaped cells with mucous-secreting goblet cells interspersed, resting on a lamina propria, with a layer of smooth muscle called muscularis mucosa. This sits on an underlying submucosa of connective tissue, surrounded by a muscularis propria of two bands of muscle, an inner circular band and an outer longitudinal one. There are a higher concentration of goblet cells in the rectal mucosa than other parts of the gastrointestinal tract.   The lining of the rectum changes sharply at the point where the rectum meets the anus. Here, the lining changes from the column-shaped cells of the rectum to multiple layers of flat cells. English rectum is derived from the full Latin expression intestinum rectum.The English name straight gut truly expresses the literal meaning of this expression, as Latin rectum means straight, and intestinum means gut. This Latin expression is a translation of the writings of Greek physician Galen. During his anatomic investigations on animal corpses, Galen observed the rectum to be straight instead of curved as in humans. The expressions and intestinum rectum are therefore not appropriate descriptions of the rectum in humans. Apeuthysmenon