Human duodenum, structure, functions

The duodenum , duodenum, begins under the liver at the level of the body of the XII thoracic or I lumbar vertebra , to the right of the vertebral column . Starting from the pylorus, the gut goes from left to right and back, then turns down and descends in front of the right kidney to level II or the top edge of the third lumbar vertebra; Then it turns to the left, at first almost horizontally, crossing the inferior vena cava in front, and then goes obliquely up in front of the abdominal aorta, and finally, at the level of the body of I or II of the lumbar vertebra, to the left of it, passes into the jejunum. Thus, the duodenum forms, as it were, a horseshoe or an incomplete ring that surrounds the top, right and bottom of the head and partly the body of the pancreas .

The initial part of the intestine is the upper part, pars superior, which at first is somewhat enlarged and forms an ampulla, ampulla; The second department is the descending part, the pars descendens, then the horizontal (lower) part, the pars horizontalis (inferior), which passes to the last department - the ascending part, the pars ascendens. When the upper part passes into the descending one, the upper bend of the duodenum, flexura duodeni superior, is noticed, and in the transition of the descending part to the horizontal part, the lower bend of the duodenum, flexura duodeni inferior. Finally, with the passage of the duodenum into the skin, the steepest twelve-perforating flexure, flexura duodenojejunalis, forms. To the back surface of the bend is a muscle that hangs the duodenum, m. Suspensorius duodeni, which is a muscular-connective tissue, attached to the left pedicle of the diaphragm. The length of the duodenum is 27-30 cm, the diameter of the widest descending part is 4.7 cm. A slight narrowing of the lumen of the duodenum is noted at the level of the middle of the length of the descending part, at the point where it intersects the right colonic artery, and on the boundary between the horizontal and ascending Parts, where the intestine is crossed from above down by the superior mesenteric vessels.

The wall of the duodenum consists of three membranes: mucous, muscular and serous. Only the beginning of the upper part (for 2.5-5 cm) is put on the peritoneum on three sides; The descending and lower parts are located retroperitoneally and are covered with adventitia.

The muscular membrane, tunica muscularis, duodenum has a thickness of 0.3-0.5 mm, larger than the thickness of the remaining parts of the small intestine. It consists of two layers of smooth muscles: the outer layer - the longitudinal layer, stratum longitudinale, and the inner - circular layer, stratum circulare.

The mucosa, tunica mucosa, consists of the epithelial layer with the underlying connective tissue plate, the muscular lamina of the mucous membrane, the lamina muscularis mucosae, and the layer of submucous loose fiber that separates the mucosa from the muscular. In the upper part of the duodenum, the mucosa forms longitudinal folds, in the descending and horizontal (lower) parts - circular folds, plicae circulares. Circular folds are constant, occupying 1/2 or 2/3 of the circumference of the gut. In the lower half of the descending part of the duodenum (rarely in the upper half), on the medial site of the posterior wall there is a longitudinal fold of the duodenum, plica longitudinalis duodeni, up to 11 mm long, distally ending with a tubercle - large papilla duodeni major, on top of which is located The mouth of the common bile duct and the duct of the pancreas. Somewhat higher, at the apex of the small papilla of the duodenum, papilla duodeni minor, there is an estuary of an additional duct of the pancreas that occurs in some cases.

The mucous membrane of the duodenum, like the rest of the small intestine, forms on its surface small outgrowths - intestinal villi, villi intestinale, up to 40 per 1 mm ² , which gives it a velvety appearance. Vorsils leaf-shaped, their height varies from 0,5 to 1,5 mm, and thickness - from 0,2 to 0,5 mm.

In the small intestine the villi are cylindrical, in the ileum - clavate.

In the central part of the villi is the lymphatic capillary. Blood vessels are directed through the entire thickness of the mucous membrane to the base of the villi, penetrate into it, and, branching to the capillary nets, reach the top of the villi. Around the base of villi, the mucous membrane forms grooves - crypts, in them open the mouth of the intestinal glands, glandulae intestinales. The glands are straight tubes, reaching the bottom of the muscular plate of the mucous membrane. They are located throughout the mucosa of the small intestine, forming an almost continuous layer and interrupting only in the places of occurrence of group lymphatic follicles. The mucous membrane of the duodenum, villi and crypts are lined with a single-layer prismatic epithelium with an admixture of goblet cells; In the deepest part of the crypts are cells of glandular epithelium. In the submucosal base of the duodenum there are branched tubular duodenal glands, glandulae duodenales; Most of them in the upper part, in the direction downwards, the number of them decreases. During the mucous membrane of the duodenum there are single lymphatic follicles, folliculis lymphatici solitarii.

Topography of the duodenum.

The upper part of the duodenum is located to the right of the body I of the lumbar or XII thoracic vertebra, a few centimeters from the pylorus intraperitoneally, so it is relatively mobile. From the upper edge of it follows the hepatic-duadenal ligament, lig. Hepatoduodenale.

The upper edge of the upper part adjoins the square lobe of the liver. To the front surface of the upper part is a gallbladder, which is sometimes connected to it with a small peritoneal ligament. The lower part of the upper part is attached to the head of the pancreas. The descending part of the duodenum is located along the right edge of the I, II and III bodies of the lumbar vertebrae. It is covered with the peritoneum on the right and front. Behind, the descending part is to the medial part of the right kidney and to the left - to the inferior vena cava. The middle of the anterior surface of the duodenum is crossed by the mesentery of the transverse colon with the right colon-intestinal artery laid in it; Above this place, the right curvature of the colon is to the anterior surface of the descending part.

At the medial edge of the descending part is the head of the pancreas, along the edge of the latter passes the anterior superior pancreato-duodenal artery, which gives feeding branches to both organs. The horizontal part of the duodenum is at level III Lumbar vertebra, crossing it from right to left, in front of the inferior vena cava; Lies retroperitoneum. It is covered with the peritoneum in front and below; Only the place of its passage into the jejunum is intraperitoneal; In this place, the peritoneal upper duodenal fold, plica duodenalis superior (plica duodenojejunalis), passes from the base of the mesentery of the transverse colon to the antiplatelet edge of it. The ascending part reaches the body of I (II) Lumbar vertebra.

On the border of the horizontal and ascending parts of the intestine, the upper mesenteric vessels (artery and vein) cross almost vertically, and to the left - the root of the mesentery of the small intestine, radix mesenterii. The posterior surface of the ascending section is attached to the abdominal aorta. The upper margin of the lower part of the duodenum adjoins the head and body of the pancreas.

A twelve-lean, flexural duodenojejunalis, fixed by a muscle suspending the duodenum, m. Suspensorius duodeni, and a bunch. The muscle consists of smooth muscle fibers; The upper end begins from the left leg of the lumbar part of the diaphragm, the lower end is weaved into the muscular membrane of the gut .

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