The length varies slightly depending on the source and how the proximal boundary is defined:
Source
Length
Yamada's Textbook of Gastroenterology
12-15 cm
Bailey & Love's Short Practice of Surgery (28th ed.)
~15 cm
Mulholland & Greenfield's Surgery
~15 cm
Sleisenger & Fordtran's GI & Liver Disease
10-12 cm
Most commonly quoted: 12-15 cm
Key anatomical points:
The rectum begins at the level of the sacral promontory (surgical definition) or the 3rd sacral vertebra (anatomical definition) - this discrepancy explains the variation in quoted lengths.
It ends at the anal canal.
It is divided into lower, middle, and upper thirds.
It lacks taenia coli, appendices epiploicae, and a well-defined mesentery.
The proximal third to half is intraperitoneal (covered by visceral peritoneum).
Full surgical mobilization of the rectum gains approximately 5 cm of additional length, which is important for deep pelvic anastomoses.
Relations:
Anterior (male): bladder, seminal vesicles, prostate, Denonvilliers' fascia
Anterior (female): uterus, cervix, pouch of Douglas
Posterior: sacrum, coccyx, Waldeyer's fascia, superior rectal vessels
Lateral: lateral ligaments, obturator internus, pelvic autonomic plexus, levator ani
Sources: Yamada's Textbook of Gastroenterology 7th ed.; Bailey & Love's Surgery 28th ed.; Mulholland & Greenfield's Surgery 7th ed.; Sleisenger & Fordtran's GI & Liver Disease
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