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Large intestine (large intestine)
Last reviewed: 23.04.2024
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The large intestine (intestinum crassum) follows the small intestine. In the large intestine, the cecum is excreted, the colorectal and the rectum. The colon is in turn represented by an ascending colonic, transverse, descending and sigmoid colon. The function of the large intestine is to absorb water, form and remove stools - undigested food residues. The length of the large intestine is about 160 cm. In living people, it is somewhat longer due to the large elasticity of the tissues. The length of the cecum in an adult is 4.66% of the entire length of the large intestine. The length of the ascending colon is 16.17%, the transverse colon is 34.55%, the descending is 13.72%, and the sigmoid colon is 29.59% of the adult large intestine (excluding the rectum). The diameter of the colon varies individually, on average it is 5-8 cm and decreases in the direction from the cecum to the rectum. The weight of the large intestine (without contents) in an adult is approximately 370 g.
The caecum is the initial part of the large intestine, and the ileum enters into it. The cecum has a saccular shape, a free dome facing downwards, from which a vermicular appendix (appendix) departs.
Less commonly, the caecum is conical. The length of the cecum is 4-8 cm. The posterior surface of the cecum is located on the iliacus and the large lumbar muscles. The anterior surface of the gut lies in the anterior abdominal wall. The cecum does not have a mesentery, but the peritoneum is covered on all sides (intraperitoneal position). The appendix is anatomically and topographically connected with the cecum, which is an important organ of the immune system.
Ascending colon (colon ascendens) has a length of 18-20 cm. The position of the ascending colon is variable. Its posterior side occupies the extreme right lateral position on the back wall of the abdominal cavity. The intestine is directed vertically upwards, located first anterior to the square muscle of the waist, then - anterior to the retroperitoneal right kidney. Near the lower (visceral) surface of the liver, the ascending colon forms a leftward and forward bend and passes into the transverse colon. This is the right (hepatic) flexure of the colon (flexura coli dextra).
The transverse colon (colon transversum) usually sags downward arcuate. Its origin is in the region of the right hypochondrium (right hepatic flexure) at the level of the costal cartilage, then the gut goes in an oblique direction from right to left first downwards, then upwards into the region of the left hypochondrium. The length of the transverse colon is about 50 cm (25 to 62 cm).
Descending colon (colon descendens) begins from the left bend of the colon down and passes into the sigmoid colon at the level of the iliac crest of the ilium. The length of the descending colon is an average of 23 cm (10 to 30 cm). The descending colon is in the left part of the abdominal cavity.
The sigmoid colon (colon sigmoideum) begins at the level of the left iliac crest and passes into the rectum at the level of the head of the sacrum. The length of the gut is from 15 to 67 cm (on average - 54 cm). Sigmoid colon forms 1-2 loops (bend) that adhere to the front of the left iliac bone and partially descend into the pelvic cavity. Sigmoid colon is intraperitoneal, has a mesentery. The presence of a mesentery causes significant mobility of the sigmoid colon.
A characteristic external feature of the caecum and the colon is the presence of three muscle bands - the bands of the colon (taeniae coli), a width of 3-6 mm each. Free, mesenteric and glandular ribbons begin at the base of the appendix and go to the beginning of the rectum. Tapes are formed due to the concentration of the longitudinal muscle layer in the three sections of the wall of the large intestine (in the region of the ribbons).
- Mesenteric tape (taenia mesocolica) corresponds to the place of attachment to the colon (to the transverse colon and sigmoid colon) of their mesenteric or gut attachment line (ascending colon and descending) to the posterior abdominal wall.
- The gland tape (taenia omentalis) is located on the front surface of the transverse colon, where a large epiploon is attached to it, and in the places of formation of the glandular processes in the other parts of the colon.
- The free tape (taenia libera) is located on the front (free) surfaces of the ascending colon and descending colon and on the lower surface of the transverse colon due to its sagging and slight twisting around the longitudinal axis.
For the walls of the colon is characterized by the presence of glandular processes - finger-like, fat-filled protrusions, covered with a visceral peritoneum. The length of the processes is 3-5 cm, and their number increases in the distal direction. The glandular processes (appendices epiploicae) play a cushioning role (presumably) with peristalsis (buffer value), serve as the body's fat stores. Over the course of the colon, due to the shorter length of the muscle bands, protrusions are formed in the intestine compared to the walls of the adjacent parts of the organ - haustra coli.
The wall of the large intestine consists of the mucous membrane, submucosal base, muscular and serous (adventitia) membranes.
The mucosa of the colon (tunica mucosa) is characterized by a significant number of transverse folds of the semilunar form. The height of the semilunar folds (plicae semilunares) ranges from a few millimeters to 1-2 cm. The folds are formed by the mucosa and the submucosa in the areas between the gut ribbons. The rectum, in its upper part (ampoule), also has transverse folds (plicae transversae recti). In the lower part (anal canal) there are 8-10 longitudinal folds. These are the anal (anal) posts (columnae anales). Between the anal columns are grooves - anal (anal) sinuses, or sinus (sinus anales). On the walls of these sinuses, the excretory ducts of 5-38 multicellular alveolar-tubular mucous anal glands open, the main sections of which are located in the submucosa base of the anal canal. The line, at the level of which the lower ends of the anal columns and the sinuses of the same type are connected, is called the rectal-anal line (hnea anorectalis).
The mucous membrane of the colon is lined with a single-layer prismatic epithelium. It is represented by three types of cells: columnar epitheliocytes (absorption cells), goblet exocrine cells and endocrinocytes. At the anal (anal) canal level, the single-layer epithelium is replaced by multilayered cubic epithelium. The abrupt transition from a multilayered cubic to a multi-layered flat non-coronary and gradually to a keratinizing epithelium is distal.
The own plate of the mucous membrane of the colon is formed by a loose fibrous connective tissue. In its thickness is 7.5-12 million colonic glands (fibricular crypts), performing not only secretory, but also suction function. In the walls of the cecum, 4.5% of the glands are located, in the walls of the colon - 90% and the rectum - 5.5% of the glands. Distribution of colonic glands has its own characteristics. The density of their location at the level of the ribbon of the colon is higher (by 4-12%) than between the bands. The gland size increases at the apex of the semilunar folds, as well as in the sphincter zones of the gut (in comparison with the intershincter zones). The walls of the glands are represented by a single-layer epithelium located on the basal membrane. Among the gland epitheliocytes, goblet and absorption cells predominate. Constantly there are undifferentiated (stem) and impermanent - endocrine cells. The number of endocrinocytes increases in the direction from the blind to the rectum. Among them there are EC cells (form serotonin and melatonin), D 2 -cells (secrete vaso-intestinal polypeptide), A-cells (secrete glucagon).
Throughout the plate of the mucous membrane of the colon, there are 5.5-6 thousand single lymphoid nodules, lymphoid and mast cells, sometimes - a few eosinophils and neutrophils. Single lymphocytes are also present in the epithelial lining of the intestine. In the thickness of the plate of the mucous membrane are blood and lymphatic capillaries and vessels, unmyelinated nerve cells of the intramural nerve plexus, nerve fibers.
The muscular plate of the mucosa is represented by bundles of smooth muscle cells forming two layers. The inner layer is oriented circularly, the outer layer is obliquely and longitudinally. From the muscle plate in the thickness of its own plate of the mucosa go the bundles of smooth muscle cells 10-30 microns long, 0.2-2.0 microns in diameter. Thin muscle bundles surround the colon and promote secretion.
The submucosa (tela submucosa) is formed by a loose fibrous connective tissue, in the thickness of which there are lymphoid nodules, submucosal nerves (Meissner's) plexus, blood and lymphatic capillaries, mucous glands (at the level of the anal canal).
The muscular membrane (tunica muscularis) of the colon, whose thickness increases in the direction from the blind to the rectum, is two muscle layers - circular (internal) continuous and longitudinal (outer) - in the form of three bands in the caecum and colon. Between these layers is the intermuscular nervous (Auerbach) plexus, represented by ganglion cells, gliocytes (Schwann and satellite cells) and nerve fibers. Ganglion cells predominate in the zones corresponding to the colon bands. The inner part of the circular layer is the zone of formation of peristaltic waves, which are generated by the interstitial nerve cells of the Kahal located in the thickness of the submucosa base on the border with the smooth musculature of the large intestine.
In some places, especially in the area of transition of one part of the large intestine to another, there are weakly expressed condensations of circularly oriented smooth muscle bundles. In these places, during digestion, narrowing of the lumen of the intestine is observed, which are called functional colonic sphincters, regulating the passage of intestinal contents. Isolate the cecal ascending sphincter, located at the level of the upper edge of the ilio-cecal valve. The next sphincter Hirsch forms a narrowing of the colon in the region of its right bending (hepatic). Three functional sphincters are defined throughout the transverse colon. The right sphincter is located at the initial part of the transverse colon. The middle transverse-sphincter and the left sphincter of Cannon are located closer to the left (splenic) crook of the colon. Directly in the region of the left flexure of the colon is the sphincter of Payra. When the descending colon recedes into the sigmoid, there is a descending-sigmoid sphincter. Within the sigmoid colon, the upper and lower sigmoid sphincters are distinguished. Sigmoid-rectum sphincter (O'Burnier) is located on the border of these two parts of the colon.
The serosa (tunica serosa) covers the colon in different ways. The blind, transverse colon, sigmoid and upper parts of the rectum are covered with the peritoneum on all sides. These parts of the colon are located intraperitoneally (intraperitoneally). The ascending colon and descending colon, as well as the middle part of the rectum, are partially covered on the peritoneum, on three sides (mesoperitoneally). The lower part of the rectum is not covered by the peritoneum. The outer shell of this part of the gut is adventitia. The peritoneum (tunica serosa) covering the large intestine, when going to the walls of the abdominal cavity or to neighboring organs, forms mesentery, numerous folds (the so-called colonic ligaments). These folds (ligaments) perform the functions of the fixing apparatus, they interfere with the displacement and lowering of the intestine, serve as ways of additional blood supply to the intestines along the blood vessels passing through them. The number of such ligaments varies individually. Upper ileo-cecal fold (plica iliocaecalis superior) represents a continuation to the right of the mesentery of the small intestine. It is attached to the medial surface of the initial part of the ascending colon, and its base is connected to the peritoneum of the right mesenteric sinus. The mesenteric ligament begins on the lower surface of the mesentery of the terminal ileum, then in the form of a triangular formation descends to the right side of the entrance wall into the small pelvis. In women, the ligament passes to the supporting ligament of the ovary, in men it goes to the deep ring of the inguinal canal, where it gradually passes into the parietal (parietal) peritoneum. The left diaphragmatic-ligament ligament (lig. Phrenocolicum sinistrum) is located between the costal part of the diaphragm and the left curvature of the colon. At the bottom, the ligament extends to the region of the splenic angle formed by the transverse colon and descending colon, connecting them with each other. Usually this ligament is fused to a large omentum. The rest of the ligaments are unstable. They often fix the areas of transition of one part of the large intestine to another.
[X-ray of the colon
X-ray examination of the colon is performed after filling it with a contrasting mass coming from the small intestine, and also through the rectum ("high contrast enema"). With the contraction of the longitudinal muscular layer, the colon shrinks, the Hausters become clearly visible. When the colon overflows with contrast mass and relaxes the longitudinal muscular bands, the gausters are smoothed out and the characteristic external signs of the colon are seen worse. Sphincters of the large intestine can also be detected during X-ray examinations. A living person has a lower location of the transverse colon than a corpse. The vermiform appendix is normally contrasted in the form of a threadlike strip of different lengths and positions. When the rectum is filled with radiocontrast mass (through the anus), its shape, dimensions and curves are determined, and the mucosal relief is traced.
Innervation of the colon (large intestine)
The colon is innervated by parasympathetic branches of the vagus nerves and sympathetic - from the upper and lower mesenteric plexuses. The rectum is innervated by parasympathetic fibers of the pelvic nerves and sympathetic fibers of the inferior hypogastric plexuses.
Blood supply to the colon (large intestine)
The colon is supplied with the upper and lower mesenteric arteries, rectal arteries (from the inferior mesenteric and internal iliac arteries). Venous outflow from the colon is carried out along the upper and lower mesenteric veins; from the rectum - along the inferior mesenteric vein, inferior vena cava (through the middle and lower rectal veins).
Outflow of lymph of the colon (large intestine)
Iliopods, pre-leukopic, intestinal lymph nodes (from the cecum and vermiform appendage); mesenteric-sedimentary, okolobobodochnye, right, middle and left colonic (from the ascending colon, transverse and descending colon); in the lower mesenteric (sigmoid) - from the sigmoid colon. From the rectum, lymph flows into the internal iliac (sacral), dorsal and upper rectal lymph nodes.