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Large intestine (colon)
Last reviewed: 04.07.2025
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The large intestine (intestinum crassum) follows the small intestine. The large intestine is divided into the cecum, colon and rectum. The colon in turn is represented by the ascending, transverse, descending and sigmoid colon. The function of the large intestine is to absorb water, form and remove feces - undigested remains of food masses. The length of the large intestine is approximately 160 cm. In living people, it is somewhat longer due to the high elasticity of the tissues. The length of the cecum in an adult is 4.66% of the total length of the large intestine. The length of the ascending colon is 16.17%, the transverse colon - 34.55%, the descending - 13.72% and the sigmoid colon - 29.59% of the length of the large intestine in an adult (excluding the rectum). The diameter of the large intestine varies individually, on average it is 5-8 cm and decreases in the direction from the cecum to the rectum. The mass of the large intestine (without contents) in an adult is approximately 370 g.
The cecum is the initial part of the large intestine, into which the ileum flows. The cecum has a sac-like shape, a free dome facing downwards, from which the vermiform appendix extends downwards.
Less commonly, the cecum is cone-shaped. The length of the cecum is 4-8 cm. The posterior surface of the cecum is located on the iliac and lumbar muscles. The anterior surface of the intestine is adjacent to the anterior abdominal wall. The cecum has no mesentery, but is covered with peritoneum on all sides (intraperitoneal position). The vermiform appendix, which is an important organ of the immune system, is anatomically and topographically associated with the cecum.
The ascending colon (colon ascendens) is 18-20 cm long. The position of the ascending colon is variable. Its posterior wall occupies the extreme right lateral position on the posterior wall of the abdominal cavity. The intestine is directed vertically upward, located first in front of the square muscle of the lower back, then in front of the right kidney located retroperitoneally. Near the lower (visceral) surface of the liver, the ascending colon forms a bend to the left and forward and passes into the transverse colon. This is the right (hepatic) flexure of the colon (flexura coli dextra).
The transverse colon (colon transversum) usually hangs down in an arc. Its beginning is in the right hypochondrium (right hepatic flexure) at the level of the 10th costal cartilage, then the intestine goes obliquely from right to left, first down, then up to the left hypochondrium. The length of the transverse colon is approximately 50 cm (from 25 to 62 cm).
The descending colon (colon descendens) begins from the left flexure of the colon downwards and passes into the sigmoid colon at the level of the iliac crest of the ilium. The length of the descending colon is on average 23 cm (from 10 to 30 cm). The descending colon is located 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 sacral promontory. The length of the intestine ranges from 15 to 67 cm (on average - 54 cm). The sigmoid colon forms 1-2 loops (bends) that are adjacent to the wing of the left ilium in front and partially descend into the pelvic cavity. The sigmoid colon is located intraperitoneally and has a mesentery. The presence of the mesentery causes significant mobility of the sigmoid colon.
A characteristic external feature of the cecum and colon is the presence of three muscular bands - the colonic bands (taeniae coli), each 3-6 mm wide. The free, mesenteric and omental bands begin at the base of the appendix and extend to the beginning of the rectum. The bands are formed as a result of the concentration of the longitudinal muscular layer in three sections of the wall of the large intestine (in the area of the bands).
- The mesenteric band (taenia mesocolica) corresponds to the place of attachment to the large intestine (to the transverse colon and sigmoid colon) of their mesenteries or the line of attachment of the intestine (ascending and descending colon) to the posterior abdominal wall.
- The omental band (taenia omentalis) is located on the anterior surface of the transverse colon, where the greater omentum is attached to it, and in places where omental processes form in other parts of the large intestine.
- The free band (taenia libera) is located on the anterior (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.
The walls of the large intestine are characterized by the presence of epiploic appendages - finger-shaped, fat-filled protrusions covered with visceral peritoneum. The length of the appendages is 3-5 cm, and their number increases in the distal direction. The epiploic appendages (appendices epiploicae) play a shock-absorbing role (presumably) during peristalsis (buffer value), serve as fat depots for the body. Along the large intestine, due to the shorter length of the muscle bands compared to the walls of adjacent areas of the organ, protrusions are formed in the intestine - haustra of the colon (haustra coli).
The wall of the large intestine consists of the mucous membrane, submucosa, muscular and serous (adventitia) membranes.
The mucous membrane of the large intestine (tunica mucosa) is characterized by a significant number of transverse folds of a crescent shape. The height of the semilunar folds (plicae semilunares) varies from a few millimeters to 1-2 cm. The folds are formed by the mucous membrane and submucosa in the areas between the intestinal ribbons. The rectum, in its upper section (ampulla), also has transverse folds (plicae transversae recti). In the lower section (anal canal) there are 8-10 longitudinal folds. These are the anal columns (columnae anales). Between the anal columns there are depressions - the anal sinuses (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 of the anal canal. The line at the level of which the lower ends of the anal columns and the sinuses of the same name are connected is called the recto-anal line (hnea anorectalis).
The mucous membrane of the large intestine is lined with a single-layer prismatic epithelium. It is represented by three types of cells: columnar epithelial cells (absorption cells), goblet exocrine cells and endocrine cells. At the level of the anal canal, the single-layer epithelium is replaced by a multilayer cuboidal epithelium. Distally, there is a sharp transition from multilayer cuboidal to multilayer flat nonkeratinizing and gradually to keratinizing epithelium.
The proper plate of the mucous membrane of the large intestine is formed by loose fibrous connective tissue. In its thickness there are 7.5-12 million colonic glands (crypts of Lieberkühn), performing not only a secretory, but also an absorptive function. In the walls of the cecum there are 4.5% of glands, in the walls of the colon - 90% and in the rectum - 5.5% of glands. The distribution of colonic glands has its own characteristics. The density of their location at the level of the colonic tapes is higher (by 4-12%) than between the tapes. The size of the glands increases at the apex of the semilunar folds, as well as in the sphincter zones of the intestine (in comparison with the intersphincter zones). The walls of the glands are represented by a single-layer epithelium located on the basal membrane. Among the epithelial cells of the glands, goblet and absorption cells predominate. Undifferentiated (stem) cells are constantly encountered and endocrine cells are inconstantly encountered. The number of endocrinocytes increases in the direction from the cecum to the rectum. Among them are EC cells (produce serotonin and melatonin), D 2 cells (secrete vasointestinal polypeptide), A cells (secrete glucagon).
Along the proper plate of the mucous membrane of the large intestine 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 proper plate of the mucous membrane there are blood and lymphatic capillaries and vessels, unmyelinated nerve cells of the intramural nerve plexus, nerve fibers.
The muscular plate of the mucous membrane is represented by bundles of smooth muscle cells that form two layers. The inner layer is oriented circularly, the outer layer is oriented obliquely and longitudinally. Bundles of smooth muscle cells 10-30 μm long and 0.2-2.0 μm in diameter extend from the muscular plate into the thickness of the proper plate of the mucous membrane. Thin muscle bundles surround the colonic glands and facilitate the removal of their secretion.
The submucosa (tela submucosa) is formed by loose fibrous connective tissue, in the thickness of which are located lymphoid nodules, submucous nerve (Meissner's) plexus, blood and lymphatic capillaries, and mucous glands (at the level of the anal canal).
The muscular coat (tunica muscularis) of the colon, the thickness of which increases in the direction from the cecum to the rectum, is two muscular layers - circular (internal) continuous and longitudinal (external) - in the form of three bands at the cecum and colon. Between these layers is the intermuscular nerve (Auerbach's) plexus, represented by ganglion cells, gliocytes (Schwann and satellite cells) and nerve fibers. Ganglion cells predominate quantitatively in the zones corresponding to the bands of the colon. The internal part of the circular layer is the zone of formation of peristaltic waves, which are generated by the interstitial nerve cells of Cajal, located in the thickness of the submucosa on the border with the smooth muscles of the colon.
In some places, especially in the area of transition of one section 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 intestinal lumen is observed, called functional colonic sphincters, regulating the passage of intestinal contents. There is an ascending cecal sphincter, located at the level of the upper edge of the ileocecal valve. The next sphincter, Hirsch's, forms a narrowing of the colon in the area of its right flexure (hepatic). Three functional sphincters are determined along the transverse colon. The right sphincter is located at the initial part of the transverse colon. The middle transverse colonic sphincter and the left sphincter of Cannon are located closer to the left (splenic) flexure of the colon. Directly in the area of the left flexure of the colon is the sphincter of Payre. At the transition of the descending colon to the sigmoid colon there is a descending sigmoid sphincter. Within the sigmoid colon, the upper and lower sigmoid sphincters are distinguished. The sigmoid-rectal sphincter (O'Bernier) is located on the border of these two sections of the large intestine.
The serous membrane (tunica serosa) covers the large intestine in different ways. The cecum, transverse colon, sigmoid colon and upper rectum are covered by the peritoneum on all sides. These parts of the large intestine are located intraperitoneally (intraperitoneally). The ascending colon and descending colon, as well as the middle part of the rectum, are partially covered by the peritoneum, on three sides (mesoperitoneally). The lower part of the rectum is not covered by the peritoneum. The outer membrane of this part of the intestine is the adventitia. The peritoneum (tunica serosa), covering the large intestine, when passing to the walls of the abdominal cavity or to adjacent organs, forms mesentery, numerous folds (the so-called colic ligaments). These folds (ligaments) function as a fixing apparatus, they prevent the intestine from shifting and descending, and serve as additional blood supply routes for the intestine through the blood vessels passing through them. The number of such ligaments varies individually. The superior ileocaecal fold (plica iliocaecalis superior) is a continuation of the mesentery of the small intestine to the right. 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-genital ligament begins on the lower surface of the mesentery of the terminal part of the ileum, then descends in the form of a triangular formation to the right edge of the wall of the entrance to 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 peritoneum. The left phrenicocolic ligament (lig. phrenocolicum sinistrum) is located between the costal part of the diaphragm and the left flexure of the colon. Below, the ligament extends to the area of the splenic angle formed by the transverse colon and the descending colon, connecting them to each other. Usually, this ligament is fused with the greater omentum. The other ligaments are inconstant. They often fix the areas of transition of one section of the large intestine to another.
[ X-ray anatomy of the colon
X-ray examination of the colon is performed after filling it with a contrast mass coming from the small intestine, as well as through the rectum ("high contrast enema"). When the longitudinal muscle layer contracts, the colon shortens, and the haustra become clearly visible. When the large intestine is overfilled with a contrast mass and the longitudinal muscle bands relax, the haustra are smoothed out and the characteristic external signs of the colon are less visible. The sphincters of the large intestine can also be detected during X-ray examinations. In a living person, the transverse colon is located lower than in a corpse. The vermiform appendix is normally contrasted as a filiform strip of varying length and position. When the rectum is filled with a radiopaque mass (through the anus), its shape, size and bends are determined, and the relief of the mucous membrane is traced.
Innervation of the large intestine (colon)
The colon is innervated by parasympathetic branches of the vagus nerves and sympathetic branches from the superior and inferior 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 blood by the superior and inferior mesenteric arteries, the rectal arteries (from the inferior mesenteric and internal iliac arteries). Venous outflow from the colon is carried out through the superior and inferior mesenteric veins; from the rectum - through the inferior mesenteric vein, the inferior vena cava (through the middle and inferior rectal veins).
Lymphatic drainage of the colon (large intestine)
Ileocolic, prececal, postcecal lymph nodes (from the cecum and appendix); mesenteric, paracolic, right, middle and left colon (from the ascending colon, transverse and descending colon); lower mesenteric (sigmoid) - from the sigmoid colon. From the rectum, lymph flows into the internal iliac (sacral), subaortic and superior rectal lymph nodes.