1. What are the physiological functions of the anorectum?
The anus and rectum are the last channels of the human digestive system. From the intake of food to the excretion of residues from the body, it is an extremely complex digestion and absorption process. This process is almost all done in the upper digestive tract. The rectum has no digestive effect, it can only absorb a small amount of water, glucose and amino acids, and stores the dregs that have been absorbed. Therefore, the main physiological function of the anorectal is to defecate. Defecation is a complex and comprehensive action. It not only includes involuntary low-level reflexes and voluntary high-level reflexes, but also requires the cooperation of abdominal muscles, diaphragm, lungs, levator ani muscle, and anal sphincter.
2. What is the clinical significance of rectal column, anal flap and anal gland?
The rectal column, also called the anal column, is the main structure of the lower rectum. Due to the contraction of the sphincter, the mucosa of the lower rectum forms 6 to 8 longitudinal strips of folds, which are clinically called the rectal column. There is a superior rectal venous plexus formed by the terminal branch of the superior rectal artery and the veins of the same name in the rectal column. These venous plexuses become varicose and expand to form internal hemorrhoids.
Anal flap: There is a half-moon-shaped mucosal fold between the lower ends of the adjacent muscle columns, called anal flap, which is the remnant of the original anorectal mucosa. The upper edge is free, the lower edge is continuous with the anal canal epithelium, and both sides are adjacent The surface layers of the anal columns are continuous, so between the anal columns, behind the anal flap, and above the tooth line, 8 to 10 small pits are formed, which are funnel-shaped, called anal crypts. In fact, the anal flap is the front wall of the anal recess, making the anal recess a pocket-like shape with the mouth facing up and the bottom facing down, with anal glands at the bottom of the recess. The anal flap is susceptible to fecal friction to cause tear-like damage. Anal fissure, anal cryptitis and other diseases can occur. The further development of anal cryptitis, the infection spreads to the anal glands, and can cause peri-anorectal abscess.
The anal glands are located at the bottom of the anal crypts, which are cup-shaped depressions on the mucosal surface between the rectal columns at the dental line. The depth of the anal crypts is about 3 to 5mm, and most of the anal crypts have anal glands at the bottom, which can secrete viscous liquid to lubricate the stool. The distribution of anal glands varies greatly among individuals, some are completely submucosal, some can penetrate deep into the sphincter layer, and some branches can pass through the internal sphincter into the combined longitudinal muscle layer. Because the anal crypt opens upward, it is susceptible to infection by fecal contamination, injury, and infection of the anal glands, forming an abscess around the rectum. Therefore, 90% of the internal mouth of anal fistula is in the anal gland.
3. What is tooth floss? What is the difference between the tooth line and the top?
The dentate line is the boundary line between the rectum and the anal canal. The lower end of the rectum has a rectal column, anal flap, anal sinus, anal papilla and other structures, and the lower edge of the rectum becomes jagged. (Also called comb line) is an important anatomical landmark. There is a big difference between the tooth line and the tooth line, so it is more important in clinical work.
4. Why does dental floss have special significance in the diagnosis and treatment of anorectal diseases?
The tooth line is not only an anatomical scoring line, but also very important in clinical medical work. Its important significance can be summarized as follows:
The tooth line is the dividing line between the skin and mucous membranes. The rectal mucosa is on the dentinal line, and most of the malignant tumors formed on the dentinal line are adenocarcinoma and mucinous carcinoma. Under the tooth line is the transitional epithelium, and the cancer formed is squamous cell carcinoma.
Since part of the blood near the dentinal line passes through the portal venous system and part passes through the inferior vena cava system, and there are communicating branches between the two at the dentinal line, when liver and spleen diseases cause the blood flow of the portal venous system to be blocked, it can be near the lower end of the rectum. Causes varicose veins to form collateral circulation. Due to the expansion of the lower rectal veins, it is easy to cause the veins to rupture and produce severe blood in the stool.
The dental line is also used to distinguish the types of hemorrhoids. Hemorrhoids that occur above the dental line are called internal hemorrhoids, the hemorrhoids below the dental line are called external hemorrhoids, and the fusion of the upper and lower hemorrhoids on the dental line is a mixed hemorrhoid.
The nerves of the rectum above the dentition are autonomic nerves. These nerves are not sensitive to pain. Therefore, diseases above the dentition, such as internal hemorrhoids, proctitis, rectal polyps, and early rectal cancer, often do not have obvious pain. The anal canal below the tooth line is innervated by spinal nerves, which are sensory nerves and are quite sensitive to pain. Such as anal fissure, inflammatory external hemorrhoids, and anal canal cancer are often characterized by pain.
Lymph from the rectum above the dentition line is the pelvic lymph nodes that flow upward into the visceral lymphatic system; if rectal cancer has lymphatic metastasis, pelvic lymph node enlargement occurs first. The lymph in the anal canal below the dentate line flows to the inguinal lymph nodes that belong to the somatic lymphatic system. When suffering from anal cancer, once lymphatic metastasis occurs, the inguinal lymph nodes will become enlarged.
The tooth line is the place where the two layers of primitive tissues, the endoderm and the ectoderm in embryonic development, fuse, so almost all anorectal congenital malformations occur near the tooth line.
5. What is anorectal ring? What are the physiological functions?
Anorectal ring refers to the general term for the sphincter group at the junction of the anal canal and the rectum. It plays a key role in maintaining the self-control of the anal canal. This ring is composed of puborectalis muscle, deep external sphincter, levator ani muscle, combined longitudinal muscle and pubococcygeus muscle.During digital rectal examination, move upward from the intersphincter groove until the upper end of the anal canal suddenly touches a clear edge back, which is the ring position. If the examinee is allowed to contract the anus, there will be a clear sensation of pinching. The anorectal ring plays an important role in maintaining the self-control of the anal canal. If this ring is completely cut off during surgery, it will inevitably cause anal incontinence. If this ring is retained, even if the sphincter is cut off, the self-control function of the anus will not have a major impact. Therefore, care should be taken to protect it during surgery. ring. If the anorectal muscle ring must be cut off during the operation, it is best to follow the midline of the anal canal. A longitudinal incision is made along the anorectal ligament. This is because some of the superficial, deep and puborectalis muscle fibers of the external anal sphincter are attached to the anorectal ligament, and some of the fibers of the puborectalis muscle are interlaced with the pubococcygeus muscle. Therefore, this incision method allows the muscle fibers to be connected with the anal-caudal ligament, and does not significantly retract, and the integrity of the anorectal ring after the operation is much better, and does not cause severe anal incomplete closure or anal incontinence. If it is necessary to cut the loop in other parts, the thread-hanging therapy can be used, that is, using thread instead of the knife. While the loop is slowly cut in about 15 days, part of the muscle fibers re-adhesion and fixation with the surrounding tissues after hanging up. When the ring is completely hung up, a considerable part of the muscle fibers have reattached to maintain the normal function of the anal canal.
At present, the understanding of the anatomy and physiology of the anorectal ring is not completely consistent, and some problems need to be studied and discussed in depth.