Is the rectum the anus?

The human body structure is a very complex structure because there are many different systems distributed in the body, and different organs are distributed in these systems. Among them, the gastrointestinal system is a very important system in the body. The rectum is an important part of the gastrointestinal system. Since the rectum and anus are connected together, many people tend to confuse the rectum and anus. So is the rectum the anus?

The concept of rectum

The concept of rectum has always been unified both internationally and domestically: the rectum is a section of the large intestine that extends 15 cm upward from the anal margin. However, in recent years, some scholars and tumor organizations, such as ASCO (2001 Clinical Guidelines for Colorectal Surgery), NIH, and NCI, have proposed new concepts about the rectum. The reasons are as follows: ① Anatomical characteristics: the large intestine larger than 12 cm is more like the colon, with mesentery instead of the rectum; ② Biological characteristics: the recurrence pattern of the large intestine larger than 12 cm is like the colon instead of the rectum; ③ In tumor therapy, it is generally believed that the rectum should be radiotherapy below the sacral promontory, because the position of the rectum below it is fixed, and the lower position is not easy to damage the small intestine; ④ During surgery, the sacral promontory is easy to mark. Two new clinical concepts of the rectum were proposed: ① During surgery, a section of the large intestine from the sacral promontory to the anal verge; ② Endoscopic examination, a section of the large intestine measured 12 cm upward from the anal verge (perianal skin) through an endoscope.

rectum

(1) The location of the rectum and its adjacent parts The rectum is the last part of the large intestine, which is about 15-16 cm long and is located in the small pelvis. The upper end connects to the sigmoid colon at the level of the third sacral vertebra, descends along the front of the sacrum and coccyx, passes through the pelvic diaphragm, and ends at the anus. The adjacent relationship between the rectum and the pelvic organs is different in men and women. The bladder, prostate and seminal vesicles are in front of the male rectum, while the uterus and vagina are in front of the female rectum. Therefore, during clinical examination, the prostate and seminal vesicles or the uterus and vagina can be palpated through the anus.

(2) The morphology of the rectum The part of the rectum above the pelvic diaphragm is called the rectal pelvis, and the lower part of the pelvis is enlarged and called the rectal ampulla. The narrowing below the pelvic diaphragm is called the anal canal or anorectal part. The rectum has two bends: the upper section convexly extends backwards, consistent with the curvature of the front of the sacrum, forming the sacral flexure; the lower section extends backwards and downwards, bypassing the tip of the coccyx, forming the perineal flexure that convexly extends forwards. When performing a sigmoidoscopy clinically, the endoscope should be inserted along the two bends of the rectum to avoid damaging the intestinal wall.

(3) Structure of the rectum The mucosa on the inner surface of the rectal ampulla forms 2 to 3 semilunar transverse rectal folds. One of them, located on the anterior right wall, is large and constant, about 7 cm away from the anus, which is equivalent to the level of the peritoneal fold. This transverse fold is often used as a landmark when determining the positional relationship between the rectal tumor and the peritoneal cavity through sigmoidoscopy. These folds serve to support stool.