1.What is the number and physiological function of rectal flaps? There are three transverse or slightly oblique semilunar mucosal folds in the inner wall of the rectum, which protrude into the intestinal cavity with the concave surface upward, called rectal flaps, also known as transverse rectal folds. There are usually three, one above and one below the left intestinal wall and one in the middle of the right intestinal wall. The number of rectal flaps varies from individual to individual, with some having two, one on each side, and some having up to five. Since the rectal flap is a half-moon shaped tissue that protrudes across the intestinal wall into the intestinal cavity, and the flap is arranged crosswise from left to right and up to down, it may prevent or stop the direct pressure exerted by the feces on the pelvic floor during defecation, causing the feces to descend, low to a certain resistance, slowing down the speed of feces running to the anus. It can also have a storage effect on small amounts of feces. Li Guodong, Department of Anorectal Medicine, Guang’anmen Hospital, Chinese Academy of Traditional Chinese Medicine 2.What is the anorectal angle? What is its physiological significance? The rectal angle of the anal canal is the angle between the lower part of the rectum and the axis of the anal canal. It is physiologically significant that the rectum and the anal canal are connected at a right angle. Since the rectum and anal canal are connected at an angle of approximately 90 degrees, when stool enters the rectum and reaches a certain amount, it stimulates the reflexes of abundant receptors near the dentate line and causes the sensation of defecation. If this angle is damaged during surgery, it can lead to fecal incontinence. Repairing this angle is one of the means of treating fecal incontinence. In addition, this form of connection at a right angle puts the posterior part of the anal canal under maximum pressure during defecation, and with the special anatomical structure near the dentate line, the posterior part of the anal canal is easily damaged and fissures occur, which can also cause infection secondary to the formation of perianal abscess. 3.Which nerves innervate the rectum of the anal canal? The perianal canal is mainly innervated by the infrahemorrhoidal nerve and anterior sphincter nerve, branches of the pubic nerve, and the perineal branch of the anal caudal nerve and the fourth sacral nerve. Therefore, local infiltration anesthesia around the anus should be injected in a circle, especially on both sides and posteriorly to infiltrate completely. The rectum is innervated by sympathetic and parasympathetic nerves, and the sympathetic nerves mainly come from the presacral plexus, which is located below the bifurcation of the aorta and divides into two branches outside the intrinsic fascia of the rectum, each downward to rendezvous with the parasympathetic nerves of the sacral region, which form the pelvic plexus on both sides of the lateral rectal ligament. Injury to the presacral nerve can cause the seminal vesicles and prostate gland to lose their ability to contract, thus preventing ejaculation and affecting fertility. The sacral parasympathetic nerve is divided from the 2nd to 4th sacral nerve, which is the main nerve that innervates urination and penile erection, and it is important to avoid damaging this nerve during perineal surgery. The sympathetic nerve can inhibit rectal peristalsis, promote secretion, and relax the anal sphincter. 4.What lymphatic reflux is there in the anal canal and rectum? There are many lymphatic tissues in the anus, anal canal and rectum, which are divided into two groups, upper and lower, with the dentate line in the anal canal as the boundary. The lymphatic tissue above the dentate line is the upper group, and below the dentate line is called the lower group. （The lymphatic tissue of the upper group starts from the lower mucosa of the rectum, and the lymphatic network of the anal canal is seen in the anal column, crossing the dentate line and going up into the rectum. The lymphatic fluid thus enters upward and backward into the perirectal lymph nodes, also called perirectal lymph nodes, which form extensive and scattered tufts outside the rectum, from which it then returns in four directions.A Upward return: upward along the superior rectal vessels and into the posterior rectal interstitial lymph nodes, which are in the sacral vault and are called posterior rectal lymph nodes. It then follows the inferior mesenteric vessels into the root mesenteric lymph nodes and converges into the peri-abdominal aortic lymph nodes. b. Returning in both directions: starting from the lymphatic network of the lower rectum, most of the lymphatic vessels travel along both sides of the inferior rectal vessels, pass through the lateral ligaments and enter the lateral rectal ligament lymph nodes. It flows back into the internal iliac lymph nodes.C Downward reflux: the lymphatic network of the submucosa of the rectum, part of which crosses the anal raphe and enters the lymph nodes of the sciatic-rectal space, or travels down the anal canal, passes through the perianal lymph nodes and enters the internal iliac lymph nodes.D Backward reflux: part of the lymphatic network of the submucosa of the rectum flows backward into the sacral lymph nodes. Lower group of lymphatic tissues: lymphatic network starting from the anus and anal canal. These lymphatic networks converge into several thick lymphatic vessels, about 8 to 10 on each side, most of which enter the superficial inguinal lymph nodes around the root of the great saphenous vein, or enter the inguinal lymph nodes along the groin outwardly via the lymphatic network of the perineum and medial subcutaneous tissues of the thigh, while another part of the lymphatic vessels enter the lymph nodes below the inguinal ligament. The lymphatic tissues of the superior and inferior groups of the dentate line have abundant anastomosing branches at the dentate line. Therefore, rectal cancer may sometimes metastasize to inguinal lymph nodes as well. According to the lymphatic reflux, the main metastatic direction of rectal cancer is upward along the superior rectal and inferior mesenteric vessels to the root lymph nodes of the inferior mesenteric vessels, and the lower rectal cancer often metastasizes to the internal iliac lymph nodes on both sides. Cancers of the anal canal and perianal skin often metastasize to inguinal lymph nodes and external iliac lymph nodes. 5.What are the sensory characteristics of the rectum? What is the physiological significance? The rectum is rich in nerves, and the rectal wall is innervated by vegetative nerves, while there are a large number of afferent nerve receptors under the rectal mucosa. Therefore, the sensory characteristics of the rectum are that it responds quickly to pressure and stimulation of intestinal contents and can stimulate the desire to defecate, but it is slow to respond to pinpricks and cuts, mainly because of the lack of spinal nerve neurons in the intestinal wall. The contraction of the external sphincter caused by rectal distension is a random action with reflex activity and cerebral cortex participation, so damage to the nerve during surgery can produce fecal incontinence even if the muscle is intact. Injury to the neurosensory apparatus in the rectum will also result in sensory anal incontinence. Therefore, many scholars advocate that the anal canal at the end of the rectum, i.e., not less than 8 cm above the anal verge, should be preserved during rectal resection in order to protect the self-control of the anorectal defecation function.