1. The state of the anus
The large intestine is the lower part of the digestive tract, starting in the right iliac fossa, then a line of abdominal cavity for a week, and finally the anal canal tooth line. The large intestine of government and enterprise is composed of the cecum and appendix, colon and rectum. The colon is composed of ascending colon, transverse colon, descending colon and sigmoid colon. Its shape in the abdominal cavity resembles a question mark, so some people say that the large intestine is the largest "?" in the human body.
According to the blood supply and walking of the large intestine, the large intestine can be divided into the right hemicolon, the left hemicolon, liver flexure and splenic flexure.
The right colon is the section from the cecum and appendix through the apex colon to most of the transverse colon (the right 5/6 of the full length), and it is supplied by the arteries on the mesenteric.
The left colon starts from a small part of the transverse colon (1/6 from the left), passes through the descending colon to the sigmoid colon, and is supplied by the inferior mesenteric artery.
Liver curvature is the unearned curvature of the transition from the ascending colon to the transverse colon, and it is also called Anfen right curvature.
Splenic flexure is the curvature formed by the transition of the transverse colon to the descending colon, also called the left intestine of the colon.
The large intestine is about 150 cm long. The main reason it is called the large intestine is its large inner diameter, about 5 to 7 cm wide. The thickest part is the cecum, and the narrowest part is the anal canal, which gradually becomes thinner in the rectum. The large intestine has the following characteristics in morphology:
(1) Each segment of the large intestine has a section, which expands outward at a certain distance, forming a constricted groove in the middle, called the colon pocket.
(2) The surface of the large intestine is tied with three longitudinal muscle bands formed by thickening the longitudinal muscles, called colon bands, which have the function of fixing the colon.
(3) A lot of protruding fat is attached to the longitudinal muscle belt of the large intestine, some are like nipple, and some are like lentils, called fat drop.
The small intestine is thinner than the large intestine, without these tissues, which are the characteristics of the large intestine.
Cecum and appendix
The cecum is the beginning of the enlargement of the large intestine, connected to the ileum, and located in the right iliac fossa. On the caudal side of the cecum is tied a tail that is about 7 to 9 cm long and shaped like an earthworm. It is the smallest section of the large intestine called the appendix, or the worm. The diameter of the vermis is very thin, and there is a well-developed lymphoid tissue in the submucosa, so some people regard the appendix as the tonsils of the abdomen.
Many parts of the entire large intestine are exposed outside the peritoneum, so extraperitoneal injuries are prone to occur, and the mobility is relatively small, but most of the cecum has a peritoneal peritoneum, so the mobility is quite large, and its position can be higher than the liver Below; low in the pelvis. Therefore, the appendix attached to it changes greatly depending on whether it is high or low. In addition, the position of the appendix in the cecum varies from person to person. Some are adjacent to the psoas muscle behind the cecum and ascending colon; some point to the pelvic cavity; some are behind the cecum; some are in front or behind the ileum. Therefore, when the appendix is inflamed, it changes in many ways and is very complicated. It adheres to the psoas muscles, and can cause psoas muscle pain when the thigh is straightened; if it is hung on the pelvic edge, when the thigh is flexed, it can cause pain in the obturator internal muscle of the buttocks; women’s Pelvic appendicitis is sometimes difficult to distinguish from salpingitis and ovarian infection, which brings difficulties to the diagnosis and treatment of appendicitis.
Rectum and anus
The adult rectum is about 12 to 15 cm long. The upper end is connected to the sigmoid colon at the third sacral level in the spine, and the lower end is connected to the anus in front of the tip of the tailbone. The rectum is actually not straight. Its shape is narrow at both ends and wide in the middle. The enlarged middle part of the intestine can accumulate a certain amount of feces, just like a teapot bulging in the middle part, so it is called the rectal ampulla . The anterior wall of the rectal ampulla bulges forward, forming a large bend almost at right angles to the anus, called rectal sacral flexion. Near the anal canal, the rectum has another sharp transition and moves to the dentate line. This curvature is called rectal perineal flexion. In this way, the rectum becomes a "curved bowel" with the upper part bent backward to the right and the lower part bent forward to the left. Why is such a curved bowel tube called rectum? This is because ancient medical scientists named them after the anatomy of animals, and the rectum of animals is relatively straight. The arrangement of the rectum determines that when the doctor performs sigmoidoscopy and proctoscopy, the direction must first point to the umbilicus, and then change to the sacrum after passing through the anal canal, in order to reach the ampulla of the rectum smoothly.
The position of the anus is exactly at the intersection of the midline of the buttocks and the transverse lines of the ischial tuberosity on both sides. It is usually oval when closed. The skin on the anal margin is loose and wrinkled, which is conducive to opening during defecation. Intradermal pigmentation, brown skin.
The section from the anal rim to the end of the rectum is called the anal canal. The adult anal canal is about 1 to 2 cm long. The skin of the anal canal is very special. The upper part is transitional epithelium; the lower part is squamous epithelium. The surface is white and smooth, without sweat glands, sebaceous glands and hair follicles. After being removed during the operation, anal skin defects, mucosal ectropion, and anal gland overflow will form. If the skin of other parts is repaired, the function is not as good as the original. Therefore, try to protect the skin of the anal canal when performing anal surgery.
Where the skin of the anal canal connects with the mucous membrane of the rectum, a serrated line is formed, called a dentate line. The dentinal line is the place where the endoderm of the primitive rectum and the ectodermal of the primitive anus intersect during the embryonic period. The upper and lower tissue structures are different. More than 85% of anorectal diseases occur near the dentinal line, which is of clinical significance (Figure 56) .
(1) Above the tooth line is the rectum, the inner wall of the intestinal cavity is covered with mucosa; below the tooth line is the anus, and the anal canal is covered with skin. Hemorrhoids above the dental line are internal hemorrhoids, and those below the dental line are external hemorrhoids; those above the dental line are polyps and tumors attached to mucous membranes, most of which are adenomas. The tumors below the dental line, attached to the skin, are skin cancers.
(2) The nerves above the dentinal line are autonomic nerves, and there is no obvious pain, so internal hemorrhoids are not painful, and are painless areas during surgery; the nerves below the dentinal line are spinal nerves, which are sensitive to pain, so external hemorrhoids and anal fissures are very painful during surgery. In the pain area, all painful anal diseases are on the tooth line.
(3) The blood vessel above the dentate line is the superior rectal blood vessel, and its vein is connected to the portal venous system; below the dentate line is the anal blood vessel, and its vein belongs to the inferior vena cava system. The portal vein communicates with the body vein near the tooth line.
(4) Lymph above the dentinal line flows upwards and flows into the pelvic lymph nodes; the lymph below the tooth line flows downwards and flows into the inguinal lymph nodes through the thighs. Therefore, the tumor metastasizes, the dentate line goes to the abdominal cavity, and the tooth line goes to the root of the thigh.
(5) The tooth line is the place where the endoderm and ectoderm of the embryo meet, so almost all congenital malformations of the anus and rectum occur at the tooth line.
The closer the rectum is to the anus, the more it shrinks and narrows, and the mucosa of the intestinal wall naturally folds up, forming many longitudinal folds and bulging outwards. This bulging fold is called the rectal column or anal column.
The semicircular fold formed between every two rectal columns is called anal flap.
The funnel-shaped fossa formed between the anal flap and the two rectal columns is called anal sinus. The anal sinus is the opening of the anal gland, which can secrete anal gland fluid, protect the anal skin and help defecation. The anal sinus is also the main gateway for anorectal shyness, and more than 80% of anal infections occur here.
Some small conical yellow-white papillary protrusions are formed where the anal canal meets the rectal column, called anal papillae. When the anal canal, rectum, or anal sinuses become inflamed, the anal papilla will become congested, edema, swelling, and hypertrophy due to inflammation. Anal papillary hypertrophy or anal papillitis develops (Figure 57).
2. The tissue structure of the colon and anus
The tissue structure of the large intestine can be divided into four layers:
(1) Mucosal layer is a layer of loose tissue inside the intestine, that is, the inner wall of the intestine. The fundamental difference between the large intestine mucosa and the small intestine is that there is no villi on the surface, so it looks smooth, shiny, red and white. Observed under a microscope, the mucosal layer is composed of a single layer of columnar epithelium and many goblet cells. It contains abundant intestinal glands. Most of the intestinal glands are straight tubular glands, which open in the intestinal mucosa and secrete fluid, protect the intestinal wall, and lubricate the stool. . There are two thin layers of smooth muscle in the mucosa, the inner layer is circular and the outer layer is longitudinal, called mucosal muscle.
(2) Submucosa is a layer of loose connective tissue under the mucosa, containing many fat cells. The blood vessels, lymphatic vessels, and nerve plexus of the large intestine wall are mainly distributed in the submucosa.
(3) The muscular layer consists of two layers. The inner layer is a neat circular smooth muscle, and the outer layer is a longitudinal smooth muscle. The three colonic bands on the surface of the large intestine are formed by the thickening of the longitudinal muscle. There are many nerve plexuses between the circular muscles and the longitudinal muscles. Under the innervation of these nerve plexuses, the muscle layer can push the feces forward through rhythmic peristalsis, and excrete the feces from the body. The muscle layer is the main source of power for the movement of the large intestine.
(4) The serosal layer is the outermost layer of the intestinal wall, which is mainly composed of connective tissue and clusters of fat cells. When the fat cells gather together, they become the fat hanging on the intestinal wall. There is mesothelium on the surface.
Although the tissue structure of the appendix and rectum is slightly different from that of the colon, they are generally composed of these four layers. Figure 58 shows the typical tissue structure of the colon.
The difference between anal tissue structure and large intestine is:
(1) The course of the anal glands is changeable. Some anal gland openings and anal gland ducts are on a vertical line (about 65%); some are not on a vertical line (about 35%), but bend and go under the tooth line, above the upper line, or the tooth line, Below. Distributed in the space between the inner and outer anal sphincter. Therefore, it is easy to be infected and form various anorectal diseases such as anal abscess, anal fistula, anal fissure, hemorrhoids, anal hypertrophy, etc.
(2) The circular muscle of the rectum becomes the internal anal sphincter when the anal canal is thickened; when the longitudinal muscle descends to the puborectalis part of the levator ani muscle, it combines with the puborectalis muscle fibers (striated muscle fibers) to form the so-called The joint longitudinal muscles are distributed around the anus.
3. Blood vessels and lymph in the anus
The blood vessels and lymph of the large intestine
Right colon, including the cecum and appendix, ascending colon, and transverse colon, most of the blood is supplied by a blood vessel called the superior mesenteric artery. Its circulating blood is supplied by a blood vessel called the superior mesenteric artery. Its circulation path is as follows:
The heart discharges blood → enters the aorta → descends to the abdominal aorta → the abdominal aorta separates the superior mesenteric artery at the level of the first lumbar vertebrae → the superior mesenteric artery separates the middle colon artery, the right colon artery, and the ileocolonic artery to the right colon .
The middle colon artery is divided into left and right branches. The left branch is distributed to the left 2/3 of the transverse colon; the right branch is distributed to the right 1/3 of the transverse colon. There is an avascular area in the middle transverse mesocolon. Therefore, doctors often perform operations through the transverse mesocolon in this area.
The right colon artery is divided into ascending and descending branches, which supply blood flow to the ascending colon and hepatic curvature.
The ileocolonic artery is also divided into two branches, which supply blood flow to the end of the ileum, the cecum and appendix, and the lower part of the ascending colon.
The left colon includes a small part of the transverse colon, descending colon, sigmoid colon, and rectum. The blood is supplied by blood vessels called the inferior mesenteric artery. Its blood flow is as follows:
From the abdominal aorta on the anterior wall of the third lumbar vertebrae level, it is divided into left colon artery, sigmoid colon artery, superior rectal artery and distributed to the left colon.
The left colon artery is also divided into ascending and descending branches, which supply blood to the sigmoid colon.
The superior rectal artery is a continuation of the main inferior mesenteric artery. It is divided into two branches at the level of the third sacral vertebrae. It descends along both sides of the rectum, passes through the muscularis of the rectum to the submucosa, and divides many small branches with the inferior rectal artery and anus. Arterial anastomosis often has main branches on the right anterior, right posterior and left side of the lower rectum. In the late stage, these branches of internal hemorrhoids become thicker and larger, and you can feel obvious pulsation, which is often the site of massive internal hemorrhoid bleeding.
These blood vessels are anastomosed with each other and communicate with each other. Therefore, mutual compensation and assistance can be achieved.
Large intestinal veins and arteries are often accompanied, called superior mesenteric vein and inferior mesenteric vein. The superior mesenteric vein collects blood from the cecum and appendix, ascending colon, transverse colon, sigmoid colon, and rectum. Then, both merge into the vein and enter the liver. Therefore, colorectal cancer easily reaches the liver when it metastases.
The lymphatic drainage of the large intestine is basically the same as that of the vein. Lymph from the right colon flows back into the superior mesenteric artery, and the lymph from the left colon flows back into the inferior mesenteric artery, then into the abdominal aorta lymph node, and finally to the chylous chest duct.
Lymph nodes on the mesentery are called paracolonic lymph nodes located on the inner edge of the colon; those located around the colonic artery and located in the area of the middle artery are called intermediate lymph nodes; those located in the main trunk area of the superior and inferior mesenteric arteries are called major lymph nodes; located on the wall of the colon and intestinal fat The inner part is called the upper colon lymph node.
The lymphatic system is one of the body's defense systems. After bacteria enter the lymph nodes, they can be swallowed and destroyed by phagocytes. However, when the bacteria are virulent and large in number, they can cause inflammation of the lymph nodes. When cancer metastasizes, it will also metastasize to the surrounding lymph nodes. Therefore, when performing radical surgery for colorectal cancer, peripheral lymph node dissection should be performed to remove the metastatic cancer cells and ensure that there will be no recurrence after surgery. At this time, it should be based on the direction of lymphatic drainage. Decide the scope of resection.
The blood vessels and lymph of the rectum and anus
In addition to the above-mentioned superior rectal artery, the blood vessels of the rectum and anus include inferior rectal artery, middle sacral artery, artery and superior rectal vein, inferior rectal vein, and vein.
The inferior rectal artery originates from the internal iliac artery and supplies blood to the anterior rectum and lower rectum.
The middle sacral artery originates from the abdominal aorta and descends along the posterior midline of the rectum. This artery is very small and has little value for blood supply to the rectum.
Egypt originates from the internal pudendal artery, one on each side of the anus, which supplies blood to the internal and external sphincter muscles of the anus, also called the anal artery.
The course and arrangement of the veins in the rectum and anus are similar to the arteries. The dentate is divided into two venous plexuses, the one above the dentate line is called the internal hemorrhoidal venous plexus, also known as the superior rectal venous plex; the one below the dentate line is called the external hemorrhoid venous plexus, also called anal venous plexus, or the inferior rectal vein Clump. The superior rectal venous plexus is more prominent in the right anterior, right posterior and left middle part of the anus. Internal hemorrhoids are most likely to occur in these three areas, which are also called maternal hemorrhoids.
Both the arteries and veins have extensive anastomosis and connection beside the dental line of the anal canal, and it is one of the places where the blood meets the blood inside and outside. So hemorrhoids can form mixed hemorrhoids when both the upper and lower venous plexus expand. Some people anastomose the upper and lower venous plexus together to form a venous network with multiple channels, also called cavernous veins.
Lymph from the anus flows down into the inguinal lymph nodes, while the lymph from the rectum flows up into the sub mesenteric lymph nodes, and finally into the lumbar lymph nodes. Therefore, anal cancer can metastasize to the inguinal lymph nodes on both sides. The surrounding skin and inguinal lymph nodes must be cleaned during surgery, while rectal cancer is easy to metastasize upwards. The upper and surrounding lymph nodes must be cleaned during surgery.
4. Innervation of the colon and anus
The large intestine is innervated by the autonomic nervous system. The autonomic nervous system is composed of sympathetic nerves and parasympathetic nerves. The two antagonize and regulate each other. Under the unified regulation of the central nervous system, they maintain the normal function of the large intestine.
Right colon The cecum, appendix, ascending colon and transverse colon are mostly innervated by the superior mesenteric plexus composed of sympathetic nerve fibers from the celiac ganglia and superior mesenteric ganglia and parasympathetic nerve fibers from the vagus nerve.
Left colon The small part of the transverse colon, descending colon, sigmoid colon, and rectum are innervated by sympathetic nerves from the inferior mesenteric plexus and pelvic nerves from the sacral center.
The anus, external anal sphincter, levator ani and the surrounding skin are innervated by the pudendal nerve from the third and fourth sacral nerves of the body. With the dentate line as the boundary, the upper part of the tooth line is innervated by autonomic nerves, and the lower part is innervated by somatic nerves. There is no pain in the upper part and pain in the lower part.
The general parasympathetic nerve excitement can enhance the peristalsis of the large intestine, promote the secretion of the glands, relax the internal anal sphincter, and discharge gas and feces; while the sympathetic nerve excitement has the opposite effect, which can resist the peristalsis of the large intestine, reduce the secretion of the glands, and make the anus The sphincter muscles contract to control the discharge of gas and feces. The alternating excitement and organic combination of the two maintain the normal activities of the large intestine.
Patients whose thoracic spine, lumbar spine and sacral spine have been ruptured due to trauma, as well as experimental animals that intentionally cut off these external nerves, have no obvious obstacles to the movement of the intestines, and can still respond to mechanical and chemical stimuli. This fact shows that the movement of the intestine is not completely controlled by the outside, but mainly depends on the sensory nerves in the intestinal wall.
Because the anus and the corpus callosum are both innervated by the pudendal nerve of the somatic nerves, anal lesions can reflexively cause spasm of the bladder and urethra and cause dysuria; on the contrary, lesions of the bladder and urethra can also reflexively cause anorectal symptoms such as tenesmus. Anal nerves are closely related to the nerves distributed to the perineum, buttocks, and thighs, so anal pain can radiate to the perineum, buttocks, and thighs.
5. Anorectal muscles
There are many muscles around the anorectum. They form the pelvic floor under the control of nerves, which carry various organs in the abdominal and pelvic cavity, control defecation, and play a very important role. The anorectal muscles include the levator ani, external anal sphincter, internal anal sphincter, and combined longitudinal muscles:
Also called the levator anus muscle, it is a pair of lamellar muscles attached to the inner wall of the pelvis. It is composed of pubococcygeus muscle, iliac coccyx muscle and puborectalis muscle. Each muscle has one on the left and right, and the two sides are connected to form a funnel-shaped pelvic floor, which carries various organs in the abdominal cavity and pelvic cavity. The most developed puborectalis muscle in the levator ani muscle tightly surrounds and fixes the anal canal. It is also the most critical muscle to control worship. After being cut off during the operation, it will cause complete incontinence of the stool, anal displacement, deformation and other serious consequences ( Figure 63).
External anal sphincter
It is located under the levator ani muscle and tightly wraps around the anal canal. It consists of the deep, superficial and subcutaneous parts of the external anal sphincter. The lower part of the skin of the external anal sphincter is an oval bone bundle located under the skin around the anus. The anus can be clearly identified. The deep and superficial parts of the external anal sphincter are generally not easily separated. Some people think that the external anal sphincter consists of the deep and The lower part of the skin consists of two layers. Cutting off the subcutaneous and superficial parts of the external anal sphincter generally will not cause fecal incontinence. Cutting the deep part will cause incomplete fecal incontinence and lose control of exhaust and loose stools.
Internal anal sphincter
It is formed by thickening and widening of the circular muscle of the rectum in the anal canal. Plays an important role in defecation reflex.
Joint longitudinal muscle
It is a mixture of the longitudinal rectal muscle at the level of the puborectalis muscle and the puborectal muscle fibers (striated muscle fibers). The descent of its muscle fibers divides the external sphincter into deep, superficial, and subcutaneous, and is distributed radially around the anal canal. It opens to the submucosa above the dentinal line to form the submucosal muscle layer; downwards, it forms under the anal skin. Corrugated cortex; in the anal canal epithelium forms the anal canal muscle. This muscle plays an important role in stretching and fixing the anorectum, preventing the rectal mucosa and anal canal from protruding, and keeping the various muscle groups in organic contact.
The above muscle groups, the levator ani muscle and external anal sphincter, are innervated by somatic nerves and are voluntary muscles that can contract or relax at will and play an important role in controlling bowel movements. The internal anal sphincter is an involuntary muscle innervated by autonomic nerves, which can control defecation through reflex activities. The combined longitudinal muscles are dually innervated by somatic nerves and autonomic nerves. They have both reflex activity and voluntary movement. There is pain. If they are injured, continuous spastic pain may occur. Therefore, the combined longitudinal muscles should be damaged as little as possible during anal surgery. Can reduce postoperative pain.
When you touch the anorectum with your fingers, you can obviously feel a rope-like muscle ring around the anal canal, which is the anorectal ring. In fact, this ring is a muscle ring composed of the puborectalis muscle and the superficial and deep parts of the external anal sphincter. It is the main structure to maintain the function of the anal sphincter. If this ring is cut off, the stool will be completely incontinent; this ring is loose and weak, and the stool will be incontinent; the narrowing of this ring will cause difficulty in defecation, so it is necessary to prevent damage to the anorectal ring during anal surgery.
6. Anorectal space
The organs and tissues of the human body are not tightly connected, but there are some gaps between them, so as to ensure the movement and expansion of the organs. There are also several gaps around the anorectum. They are:
The pelvic-rectal space is located between the upper rectum and the pelvis, above the levator ani muscle. One on each side.
The posterior rectal space is located between the upper rectum and the anterior sacral fascia, above the levator ani muscle.
The ischiorectal space is located in the fossa formed by the ischia and rectum, so it is also called the ischiorectal fossa, under the levator ani muscle. One on each side.
The posterior anal space is located behind the anus, between the skin and the levator ani muscle, and is divided into deep and shallow parts by the superficial layer of the external anal sphincter. The two sides of the deep part are connected to the ischiorectal space. Therefore, the ischiorectal fossa can spread through the posterior anus space to the opposite side to form a so-called shoe-shaped anal fistula.
These gaps are full of fatty tissue and connective tissue, which are easily inflamed by bacteria, and eventually form anorectal abscess and anal fistula.