1.What is the number and physiological function of the rectal flap?
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 the rectal flap, also known as the transverse rectal fold. 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 crossed up and down to the left and right, 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. For a small amount of feces can also play a storage role.
2.What is the rectal angle of the anal canal? What is the physiological significance?
The rectal angle is the angle between the lower part of the rectum and the axis of the anal canal. Rectum and anal canal right angle connected in the physiological significance. Since the rectum and anal canal are connected at an angle of about 90 degrees, when stool enters the rectum and reaches a certain amount, it can provoke the reflex of abundant receptors near the dentate line and cause 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 inferior hemorrhoidal 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 in 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, and the lymphatic capillaries at the bottom of the anal column converge into lymphatic tubules along the anal column and go up to the lower mucosa of the rectal jugular, and when it reaches the upper end of the anal column, the lymphatic network is very rich. The lymphatic fluid thus enters upward and backward into the perirectal lymph nodes, also called perirectal lymph nodes, which form an extensive and scattered plexus outside the rectum, from which it then flows back in four directions.
A Upward reflux: upward along the superior rectal vessels and into the posterior rectal space lymph nodes, which are in the sacral vault and are called posterior rectal lymph nodes. It then follows the inferior mesenteric vessels into the mesenteric root lymph nodes and converges into the peri-abdominal aortic lymph nodes.
B reflux to both sides: starting from the lymphatic network of the lower rectum, most of the lymphatic vessels travel along both sides of the inferior rectal vessels, passing through the lateral ligaments and into the lymph nodes of the lateral rectal ligaments. It flows back into the internal iliac lymph nodes.
C Downward reflux: the lymphatic network of the submucosa of the rectum, some 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: some 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 tissue of the thigh, and 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, and 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 neurons of the spinal nerve in the intestinal wall. The contraction of the external sphincter caused by rectal distention is a random action with reflex activity and participation of the cerebral cortex, 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.