home Polyps The folds of the small intestine are composed of. Small intestine. Small intestine wall structure

The folds of the small intestine are composed of. Small intestine. Small intestine wall structure

The small intestine (intestinum teniae) is the section of the digestive system following the stomach, 2.8 to 4 m long, ends with an ileocecal valve in the right iliac fossa. On a corpse, the small intestine reaches a length of up to 8 m. The small intestine is subdivided without particularly clear boundaries into three sections: duodenum (duodenum), jejunum (jejunum), ileum (ileum).

In terms of its functional significance, the small intestine occupies a central place in the digestive system. In its lumen, under the action of intestinal juice (volume 2 l), pancreatic juice (volume 1-2 l) and liver bile (volume 1 l), the final splitting of all nutrients into their constituent parts occurs: proteins are broken down to amino acids, hydrocarbons - to glucose , fats - to glycerin and soap. Digestive products are absorbed into the blood and lymph vessels. It is characteristic that all the split substances must dissolve in water, forming isotonic solutions. Only in this form is their resorption possible through the intestinal epithelium. In the thickness of the intestinal wall, in the blood, lymph and liver, protein, fat and glycogen are synthesized from the incoming nutrients.

All parts of the small intestine have a common structure. The intestinal wall consists of membranes: mucous, submucosa, muscular and serous.

The mucous membrane (tunica mucosa) is covered with a single-layer prismatic edged epithelium. Each cell on the side facing the intestinal cavity has up to 3000 microvilli, which in a light microscope look like a border. Due to the microvilli, the absorbing surface of the cells increases 30 times. Along with prismatic cells, there are solitary goblet cells that produce mucus. Under the epithelium is a delicate connective tissue basal plate, separated from the submucosa of the lamina muscularis. The surface of the mucous membrane contains circular folds (plicae circulares), numbering about 600, and 30 million villi (villi intestinales) 0.3-1.2 mm high. The villus is a finger-like protrusion of the mucous membrane (Fig. 238). The villus contains loose connective tissue, smooth muscle fibers, arteries and veins. In the central part lies a blind outgrowth of the lymphatic capillary, called the lactiferous sinus (Fig. 239). Depressions are visible between the villi - about 150 million crypts of the mucous membrane; crypts arise as a result of invagination of the basement membrane towards the ducts of the intestinal glands (gll.intestinales). Due to the presence of microvilli, circular folds, villi and crypts, the absorption surface of the mucous membrane in comparison with a flat surface on an equivalent section of the intestine increases 1000 times. This fact is an extremely important adaptive moment that ensured the development of a relatively short intestine in humans, but due to the large area of \u200b\u200bthe mucous membrane, it has time to resorb almost all nutrients from the gastrointestinal tract.

The submucosa (tela submucosa) is loose, very mobile, almost throughout the small intestine. In the submucosa of the duodenum, the end sections of the gll lie. duodenales. Their secret is poured into the intestines. The secret of the crypt glands contains enterokinase, which activates the trypsinogen of pancreatic juice. In the initial section of the duodenum, there are still glands that produce pepsin and dipeptidase for the breakdown of proteins. In the submucosa, there is an accumulation of lymphatic tissue in the form of follicles.

The muscular membrane (tunica muscularis) consists of smooth muscles that form the inner, circular and outer longitudinal layers. Their thickness is much less than in the stomach wall. Starting from the bulb of the duodenum towards the end of the small intestine, the muscular membrane thickens. Circular fibers forming a steep spiral are able to reduce the intestinal lumen. Longitudinal muscle fibers cover the intestine in a gentle spiral with a turn of the turn of 20-30 cm, causing a shortening of the intestinal tube and the formation of pendulum movements.

Serous membrane - peritoneum (tunica serosa), with the exception of the duodenum, covers the small intestine from all sides, forming the intestinal mesentery. The peritoneum is covered with mesothelium and has a connective tissue base.

Duodenum

The duodenum (duodenum), 25-30 cm long, begins with a bulbous extension from the pyloric sphincter and ends with the duodenal bend (flexura duodenojejunal), connecting it with the jejunum (Fig. 240). In comparison with other parts of the small intestine, it has a number of structural features and, naturally, functions and topography. It should be noted that pathological processes often occur in the duodenum, as well as in the stomach, sometimes requiring not only therapeutic treatment, but also surgical intervention. This circumstance imposes certain requirements on the knowledge of anatomy.

The duodenum is devoid of a mesentery and its posterior surface is accreted to the posterior abdominal wall. The most typical (60% of cases) is an irregular horseshoe shape of the intestine (Fig. 240), in which the upper (pars superior), descending (pars descendens), horizontal (pars horizontalis inferior) and ascending (pars ascendens) parts are distinguished.

The upper part is a segment of the intestine from the pyloric sphincter to the upper bend of the duodenum, 3.5-5 cm long, 3.5-4 cm in diameter. The upper part is adjacent to m. psoas major and to the body of the I lumbar vertebra on the right. There are no folds in the mucous membrane of the upper part. The muscle layer is thin. The peritoneum covers the upper part mesoperitoneally, which makes it more mobile than other parts. The upper part of the intestine from above is in contact with the square lobe of the liver, in front - with the gallbladder, behind - with the portal vein, common bile duct and gastro-duodenal artery, from below - with the head of the pancreas (Fig. 241).

The descending part of the duodenum is 9-12 cm long, 4-5 cm in diameter. It starts from the upper bend (flexura duodeni superior) and at the level of the I lumbar vertebra to the right of the spinal column and ends with the lower bend at the level of the III lumbar vertebra.

In the mucous membrane of the descending part, circular folds, conical villi are well pronounced. In the middle zone of the descending part of the intestine, the common bile duct and the pancreatic duct open on the posteromedial wall. The ducts pierce the wall obliquely and, passing in the submucosa, raise the mucous membrane, forming a longitudinal fold (plica longitudinalis duodeni). At the lower end of the fold there is a large papilla (papilla major) with an opening of the ducts. 2-3 cm above it there is a small papilla (papilla minor), where the mouth of the small pancreatic duct opens. When the ducts of the pancreas and the common bile duct pass through the muscular wall, it transforms and forms circular muscle fibers around the mouths of the ducts, forming a sphincter (m. Sphincter ampullae hepatopancreaticae) (Fig. 242). The sphincter is anatomically associated with the muscular layer of the intestine, but functionally independent, being under the control of the autonomic nervous system, as well as chemical and humoral stimuli. The sphincter regulates the flow of pancreatic juice and liver bile into the intestine.

The descending part is inactive; it is located behind the peritoneum and is fused with the posterior abdominal wall, the head of the pancreas and its duct, as well as with the common bile duct. This part is crossed by the mesentery of the transverse colon. The descending part of the duodenum is in contact in front with the right lobe of the liver, behind - with the right kidney, inferior vena cava, laterally - with the ascending part of the large intestine, medially - with the head of the pancreas.

The horizontal part starts from the lower bend of the duodenum, has a length of 6-8 cm, crosses the body of the III lumbar vertebra in front. In the mucous membrane, circular folds are well pronounced, the serous membrane covers the horizontal part only in front. The horizontal part of the upper wall is in contact with the head of the pancreas. The posterior intestinal wall is adjacent to the inferior vena cava and right renal veins.

The ascending part continues from the horizontal part of the duodenum, its length is 4-7 cm. It is located to the left of the spine and at the level of the II lumbar vertebra passes into the jejunum, forming a duodenal bend (flexura duodenojejunalis). The ascending part crosses the mesentery root of the jejunum. Between the anterior wall of the ascending part of the duodenum and the body of the pancreas, the superior mesenteric artery and vein pass. The ascending part of the duodenum is in contact from above with the body of the pancreas, in front - with the mesentery root, behind - with the inferior vena cava, aorta and left renal vein.

With an upright position of a person and a deep breath, the duodenum descends by one vertebra. The most loose parts are the bulb and the ascending part of the duodenum.

Duodenal ligaments... The hepatoduodenal ligament (lig.hepatoduodenale) is a double sheet of the peritoneum. It starts from the upper posterior wall of the upper part of the duodenum, reaches the gate of the liver, limiting the right edge of the lesser omentum, and is part of the anterior wall of the opening of the omental bursa (see Structure of the peritoneum). At the edge of the ligament on the right lies the common bile duct, on the left - the own hepatic artery, the posterior portal vein, the lymphatic vessels of the liver (Fig. 243).

Duodenal - renal ligament (lig. Duodenorenale) - a wide plate of the peritoneum, stretched between the posterior upper edge of the upper part of the intestine and the area of \u200b\u200bthe hilum of the kidney. The ligament forms the bottom wall of the stuffing box opening.

Duodenal - transverse colon ligament (lig. Duodenocolicum) is the right part of the lig. gastrocolicum, runs between the transverse colon and the upper part of the duodenum. The ligament runs the right gastroepiploic artery for the stomach.

Suspension ligament (lig. Suspensorium duodeni) is a duplication of the peritoneum, which covers the fiexura duodenojejunalis and is attached at the beginning of the superior mesenteric artery and to the medial legs of the diaphragm. In the thickness of this ligament, there are smooth muscle bundles.

Variants of the shape of the duodenum... The bowel shape described above occurs in 60% of cases, folded - in 20%, V-shaped - in 11%, C-shaped - in 3%, ring-shaped - in 6% (Fig. 244).

In newborns and children of the first year of life, the duodenum is comparatively longer than in an adult; the lower horizontal part is especially long. The folds of the mucous membrane are low, the digestive glands of the intestine are well developed, and its parts are not differentiated. The shape of the intestine is annular. A feature is also the place of confluence of the pancreatic duct and the common bile duct, which flow into the initial section of the duodenum.

Jejunum

The jejunum represents 2/5 of the length of the mesenteric part of the small intestine. Starting from flexura duodenojejunalis on the left at level II of the lumbar vertebra, the jejunum ends with an ileocecal valve. The diameter of the small intestine is 3.5-4.5 cm. The mucous membrane contains well-defined circular folds 5-6 mm high, covering 2/3 of the intestine circumference, containing villi and crypts. In the submucosa, not only the end sections of the intestinal glands lie, but also the lymphatic follicles (folliculi lymphatici solitarii) (Fig. 245). Lymphocytes with immunobiological properties are formed in follicles. Once in the blood and lymph, they are carried throughout the body. Some of the lymphocytes penetrate the surface of the mucous membrane and die in the digestive zone, releasing enzymes that facilitate digestion.

Ileum

The ileum (ileum), represents 3/5 of the end of the small intestine and ends with the ileocecal valve. The diameter of the ileum is 2-2.5 cm. Its loops occupy the pelvic cavity and the right iliac region. The mucous membrane in the initial part of the intestine has circular folds, which are absent in the final section. Single and combined lymphatic follicles (folliculi lymphatici agregati et solitarii) lie in the submucosa. The follicles are clearly visible, since the mucous membrane has few villi and folds (Fig. 246).

The terminal part of the ileum, 10-12 cm long, is accreted to the posterior abdominal wall, does not have a mesentery, and is covered with a peritoneum on three sides.

The difference between the ileum and the jejunum: 1) the diameter of the jejunum is larger than the ileum; 2) the wall of the jejunum is thicker, has more folds in the mucous membrane and thick-lying villi; 3) the jejunum is abundantly supplied with blood, therefore it has a pink tint; 4) there are no united lymphatic follicles in the jejunum; single and united lymphatic follicles, better developed in the ileum.

Jejunum constitutes the proximal part of the small intestine, and the ileum - distal; however, there is no clear boundary between them. In the distal parts, the intestinal wall becomes thinner, the lumen narrows, the mesentery of the ileum contains a greater amount of fat, and the architectonics of the arterial arcades is more complex. The small intestine is anchored proximally by retroperitoneal fixation of the duodenum with the Treitz ligament, and the distal end is relatively motionless due to fixation of the cecum to the posterior wall of the abdominal cavity. Between these two areas, the intestine, due to the pronounced mesentery, is quite mobile.
Normally, the length is at least 2 m (it can reach 3.5 m), after death, due to relaxation of the smooth muscles of the intestinal wall, it reaches 6 m or more.

In the proximal part jejunum and in the postbulbar part of the duodenum there are numerous and well-developed circular folds (valvulae conniventes), or Kerkring folds. In the distal part of the ileum, they are usually absent, and their degree of severity is a characteristic X-ray sign, which makes it possible to distinguish different parts of the small intestine from each other.

A - Normal endoscopic picture of the jejunum, rigid endoscope "pushing" type
B - Normal passage of barium through the small intestine
B - Sighting radiograph of the normal small intestine. Circular folds are clearly visible - the loops of the small intestine are swollen and do not overlap (black arrow), overlap or not swollen (white arrow), circular folds form a "thin" pattern

Small intestine mucosa has many finger-shaped villi, the surface of which consists of enterocytes and individual goblet cells. Intestinal crypts, or Lieberkun's glands, open between the bases of the villi. In the duodenum, the villi are wide, leaf-shaped or spatulate. In the jejunum, most of the villi are digital; as they move towards the ileum, they become longer and thinner, these features are clearly visible on microscopy. It should be noted that the number of leaf-shaped villi in the proximal part of the small intestine is higher in people living in the tropics, even if we take into account the moderate partial atrophy of the villi, but the ratio between the height of the villi and the depth of the crypt remains within the normal range and ranges from 3: 1 to 4: 1.

Enterocytes - relatively uniform prismatic epithelial cells, which play a key role in secretion and absorption, in part due to the brush border formed by microvilli. The life cycle of enterocytes is 2-3 days - one of the shortest in the body. At the base of the crypt, there is a continuous renewal of intestinal stem cells (enteroblasts), their movement to the tops of the villi is accompanied by differentiation.

There are more goblet cells in ileum... The villi also contain M cells and bundle cells. M cells, which do not have microvilli, are located in the area of \u200b\u200bPeyer's patches and provide a connection between the intestinal lymphoid tissue and the processes taking place in its lumen. The bundle cells have pronounced microvilli, but their function is still unknown. Normally, epithelial lymphocytes are present, but in healthy people there are no more than 40 of them for every 100 enterocytes. The crypts contain acidophilic intestinal cells (Paneth cells) and endocrine cells of the APUD system, including L-cells that secrete intestinal hormones - glucagon-like peptides. The lamina propria forms the base of the villi and consists of connective tissue with blood and lymph vessels. It contains a small number of lymphoid cells, eosinophils and histiocytes.

It is the longest section of the digestive tract. It is located between the stomach and large intestine. In the small intestine, food gruel (chyme), treated with saliva and gastric juice, is exposed to the action of intestinal juice, bile, pancreatic juice; here the digestion products are absorbed into the blood and lymph vessels (capillaries). The small intestine is located in the womb (middle region of the abdomen) downward from the stomach and transverse colon, reaching the entrance to the pelvic cavity. The length of the small intestine in a living person ranges from 2.2 to 4.4 m, in men the intestine is longer than in women. In a corpse, due to the disappearance of muscle tone, the length of the small intestine is 5-6 m. The small intestine has the shape of a tube, the diameter of which at its beginning is on average 47 mm, and at the end - 27 mm. The upper border of the small intestine is the pylorus, and the lower is the ileocecal valve at the place of its confluence into the cecum.

The small intestine has the following divisions:

The duodenum;
The jejunum;
Ileum;

The jejunum and ileum, in contrast to the duodenum, have a well-defined mesentery and are considered as the mesenteric part of the small intestine.

The duodenum does not have a mesentery, it is located retroperitoneally. The peritoneum is adjacent to the intestine in front, except for those places where it is crossed by the root of the transverse colon and the root of the mesentery of the small intestine. The initial section of the duodenum - its ampulla (bulb) is covered by the peritoneum on all sides. On the inner surface of the wall of the duodenum, circular folds characteristic of the entire small intestine are visible, as well as longitudinal folds that are present in the initial part of the intestine, in its ampulla. In addition, the longitudinal fold of the duodenum is located on the medial wall of the descending part. In the lower part of the fold there is a large duodenal papilla where the common bile duct and pancreatic duct open with a common opening. Above the large papilla, there is a small duodenal papilla on which the opening of the accessory pancreatic duct is located. Duodenal jellies open into the lumen of the duodenum. They are located in the submucosa of the intestinal wall.

Vessels and nerves of the duodenum. The upper anterior and posterior pancreatoduodenal arteries (ie gastroduodenal artery) and the lower pancreatoduodenal artery (ie superior mesenteric artery), which anastomose with each other and give the duodenal branches to the intestinal wall, are suitable for the duodenum. Veins of the same name flow into the portal vein and its tributaries. The lymphatic vessels of the intestine are directed to the pancreatoduodenal, mesenteric (upper) celiac and lumbar lymph nodes. The innervation of the duodenal ulcer is carried out by the straight branches of the vagus nerves and from the gastric, renal and superior mesenteric plexuses.

X-ray anatomy of the duodenum

Allocate the initial section of the duodenum called "bulb", which is visible in the form of a triangular shadow, and the base of the triangle is facing the pylorus and is separated from it by a ueka constriction (contraction of the pylorus sphincter). The top of the "bulb" corresponds to the level of the first circular fold of the duodenal mucosa. The shape of the duodenum varies individually. So, the horseshoe shape, when all its parts are well expressed, occurs in 60% of cases. In 25% of cases, the duodenum has the shape of a ring and in 15% of cases - the shape of a loop, located vertically, resembling the letter "U". Transitional forms of the duodenum are also possible. The mesenteric part of the small intestine, into which the duodenum continues, is located below the transverse colon and its mesentery and forms 14-16 loops, covered in front by a large omentum. Only 1/3 of all loops are on the surface and can be viewed, and 2/3 lie in the depths of the abdominal cavity and for their examination it is necessary to straighten the intestine. About 2/5 of the mesenteric part of the small intestine belongs to the jejunum and 3/5 to the ileum. There is no clear-cut border between these parts of the small intestine.

The jejunum is located immediately after the duodenum, its loops lie in the upper left part of the abdominal cavity.

The ileum, being a continuation of the jejunum, engages the lower right abdominal cavity and flows into the cecum in the region of the right iliac fossa. The jejunum and ileum are covered on all sides by the peritoneum (lie intraperitoneally), which forms the outer serous membrane of its wall, located on a thin subserous base. Due to the fact that the peritoneum approaches the intestine on one side, a smooth free edge covered with a peritoneum and an opposite mesenteric edge, where the peritoneum covering the intestine passes into its mesentery, is isolated from the jejunum and ileum. Between the two sheets of the mesentery, arteries and nerves approach the intestine, veins and lymphatic vessels exit. Here on the intestine there is a narrow strip not covered by the peritoneum. The muscular membrane lying under the subserous base contains the outer longitudinal layer and the inner circular layer, which is better developed than the longitudinal one. At the confluence of the ileum into the blind, there is a thickening of the circular muscle layer. The submucosa next to the muscular membrane is rather thick. It consists of loose fibrous connective tissue, which contains blood and lymph vessels, nerves.

The inner mucosa is pink at the level of the duodenum, jejunum and grayish-pink at the level of the ileum, which is explained by the different intensity of blood supply to these parts. The mucous membrane of the wall of the small intestine forms circular folds, the total number of which reaches 650. The length of each fold is 1 / 2-2 / 3 of the intestine circumference, the height of the folds is about 8 mm. The folds are formed by the mucous membrane with the participation of the submucosa. The height of the folds decreases in the direction from the jejunum to the ileum. The surface of the mucous membrane is velvety due to the presence of outgrowths - intestinal villi 0.2-1.2 mm long. The presence of numerous (4-5 million) villi, as well as folds, increases the absorption surface of the mucous membrane of the small intestine, which is covered with a single-layer prismatic tissue and has a well-developed network of blood and lymph vessels. The basis of the villi is the connective tissue of the lamina propria of the mucous membrane with a small number of smooth muscle cells. The villus contains a centrally located lymphatic capillary - the lactiferous sinus. An arteriole enters each villus, which divides into capillaries, and venules exit from it. The arteriole, venules and capillaries in the villus are located around the central lactiferous sinus, closer to the epithelium. Among the epithelial cells that cover the mucous membrane of the small intestine, goblet cells that secrete mucus (unicellular glands) are found in large numbers. On the entire surface of the mucous membrane between the villi, numerous tubular intestinal glands open, secreting intestinal juice. They are located in the thickness of the mucous membrane. In the mucous membrane of the small intestine, numerous single lynphoid nodules are localized, the total number of which in young people reaches an average of 5000. In the mucous membrane of the ileum there are large accumulations of lymphoid tissue - lymphoid plaques (Peyer's patches) - group lynphoid nodules, the number of which ranges from 20 to 60. They are located on the side of the intestine, opposite its mesenteric edge, and protrude above the surface of the mucous membrane. Lymphoid plaques are oval, their length is 0.2-10 cm, width is 0.2-1.0 cm or more.

Vessels and nerves of the jejunum and ileum

15-20 small bowel arteries (branches of the superior mesenteric artery) are suitable for the intestine. Venous blood flows through the veins of the same name into the portal vein. Lymphatic vessels flow into the mesenteric (upper) lymph nodes, from the terminal ileum - into the ileal-colonic nodes. The innervation of the small intestine wall is carried out by the branches of the vagus nerves and the superior mesenteric plexus (sympathetic nerves).

X-ray anatomy of the jejunum and ileum

X-ray examination allows you to see the position and relief of the mucous membrane of the small intestine. The loops of the jejunum are located on the left and in the middle of the abdominal cavity, vertically and horizontally, the loops of the ileum are located in the right lower abdomen (some of its loops descend into the small pelvis), vertically and in an oblique direction. The small intestine on radiographs is visible in the form of a narrow tape 1-2 cm wide, and with a reduced wall tone - 2.5-4.0 cm.The contours of the intestine are uneven due to circular folds protruding into the intestinal lumen, the height of which on radiographs is 2-3 mm in the jejunum and 1–2 mm in the ileum. With a small amount of X-ray contrast mass in the lumen of the bowel ("weak" filling), folds are clearly visible, and with "tight" filling (a lot of mass was introduced into the lumen of the intestine), the size, position, shape and contours of the intestine are determined.

Fig. 1.Scheme of the location of the abdominal organs

1- hepar, 2- vesiсa fellea, 3- ductus choledochus, 4- pars cardiaca ventriculi, 5- fundus ventriculi, 6- curvatura venlriculi minor, 7- corpus ventriculi, 8- lien, 9- curvatura ventriculi major, 10- colon transversurn , 11- jejunum, 12- colon descendens, 13- colon sigmoideum, 14- rectum, 15- appendix vermiformis, 16- caecum, 17- ileum, 18- colon ascendens, 19- duodenum, 20- pars pylorica ventriculi

Traditionally, there are three divisions of the small intestine: the duodenum (Duodenum), the jejunum and the ileum. Most of the small intestine, except for the initial part of the duodenum, is located in the lower floor of the abdominal cavity (below the mesentery of the transverse colon) before entering the small pelvis, projecting onto the anterior abdominal wall in the mesogastrium and, partially, in the hypogastrium. The length of the small intestine is about 6-7 meters, the average transverse dimension in the distal direction is from 47 to 27 mm. In the small intestine, the process of digestion of food coming from the stomach is completed, as well as the absorption of digestion products and water into the blood and lymphatic vascular bed through the capillaries of the intestinal wall.

The presented methodological manual is aimed at describing the structure and surgical pathology of the jejunum and ileum, as the most similar parts of the small intestine, while the duodenum has significant features and it is advisable to consider it separately. Therefore, the term "small intestine" is to be understood hereinafter only as the jejunum and the ileum.

The jejunum and the ileum are parts of a single intestinal tube passing into each other from the duodeno-jejunal bend to the ileocecal foramen - the place of transition to the large intestine (Fig. 2). The border between the jejunum and the ileum is conditional, i.e. they are similar in anatomical, histological and physiological terms. With a total length of about 6-6.5 m, the ratio of the length of the jejunum to the ileum is 2: 3. The diameter of the intestine decreases from 4 cm to 2.5-3 cm. The jejunum and ileum are located in the lower floor of the abdominal cavity, lie intraperitoneally, therefore they are a well-mobile part of the intestine. With respect to the spinal column, the loops of the jejunum are predominantly located in the left half of the abdominal cavity, and the ileum in the right.

The initial part of the small intestine (jejunum) starts from the duodeno-jejunal flexure (flexura duodenojejunalis), located on the left antero-lateral surface of the II lumbar vertebra (Fig. 2.5). The duodeno-jejunal bend is fixed to the diaphragm by a suspension ligament of the duodenum (lig. Suspensorium duodeni, Treitz's ligament), which includes a muscle that suspends the duodenum (m. Suspensorium duodeni).

Fig. 2. Small intestine and mesenteric vessels

(the mesentery of the small intestine is tilted to the left)

1- ileum, 2- appendix, 3- cecum, 4- artery and vein of the appendix, 5- ileal arteries and veins, 6- ascending colon, 7- ileal-colon artery and vein, 8- duodenum, 9- right colon arthria, 10- pancreas, 11- middle colonic artery, 12- superior mesenteric vein, 13- superior mesenteric artery, 14- transverse colon, 15- jejunum, 16- jejunal arteries and veins, 17- duodeno -junal bend

The ligament is an important surgical landmark, formed by the folds of the peritoneum to the left of the bend: the upper duodenal fold (plica duodenalis superior), in which the inferior mesenteric vein (v. Mesenterica inferior) and the lower duodenal fold (plica duodenalis inferior) pass. There are pockets between them: the upper duodenal pocket (recessus duodenalis superior), located behind the upper duodenal fold; paraduodenal pocket (recessus paraduodenalis) - between the upper and lower duodenal folds; lower duodenal pocket (recessus duodenalis inferior) - behind the lower duodenal fold. These pockets are predisposing factors for the formation of internal hernias (Treitz hernia).

Syntopically, the duodeno-jejunal bend from above and from the front is adjacent to the mesentery of the transverse colon; on the right - to the superior mesenteric vessels and the middle colic artery (a. colica media), starting from the superior mesenteric artery after its exit from under the pancreas and going into the mesentery of the transverse colon; on the left in the upper duodenal fold lies the lower mesenteric vein; below is the beginning of the root of the mesentery of the jejunum. In operations to find the duodenal bend and the initial part of the jejunum, use reception of Gubarev... In this case, the great omentum (omentum majus) with the transverse colon is captured by the left hand of the surgeon and leans upward, the mesentery of the transverse colon is stretched. The right hand, immediately below the root of the mesentery of this intestine, is placed on the spine, as a rule, on the II lumbar vertebra.

On the left surface of the vertebral body, a loop of the intestine is found with the fingers. If it is fixed to the posterior wall of the abdomen, then this is the duodenal flexure, distal to which the jejunum begins.

The jejunum and the ileum have a common mesentery (mesenterium), formed by two sheets of the peritoneum, between which neurovascular formations, lymph nodes and adipose tissue are enclosed. Distinguish between mesenteric, where the mesentery is attached, and free edges (margo mesentericus et margo liber) of the intestine . On the mesenteric edge between the sheets of the peritoneum there is a strip of the intestinal wall, which is devoid of the peritoneum (pars nuda) (Fig. 3).

The inner surface of the intestinal wall has a folded velvety appearance due to circular (kerkring) folds (plicae circularis) and numerous intestinal villi (Fig. 3, 9).

Fig. 3 Wall of the small intestine in section

1- circular folds of the mucous membrane, 2- pars nuda of the mesenteric edge

The root of the mesentery (radix mesenterii) (Fig. 4) - the place of attachment of the small intestine to the posterior abdominal wall - has an oblique direction, stretches from the left edge of the II lumbar vertebra to the right sacroiliac joint, ending in the right iliac fossa. The length of the mesentery root of the small intestine is 15-23 cm. The distance from the mesentery root to the intestinal wall increases from the jejunum to the ileum from 13 cm to 20-25 cm. The amount of fatty tissue in the mesentery increases from the initial part of the jejunum to the terminal part of the ileum.

To the right of the mesenteric root to the ascending colon is the deepening of the abdominal cavity - the right mesenteric sinus (sinus mesentericus dexter), and to the left to the descending colon is the left mesenteric sinus (sinus mesentericus sinister). The left mesenteric sinus opens into the small pelvis from below. The sinuses are connected from above by a narrow gap between the mesentery of the transverse colon and the duodeno-jejunal flexure. The mesenteric sinuses contain the bulk of the small intestine. The clinical significance of the sinuses - the spread of inflammatory effusion in the abdominal cavity and into the small pelvis. Syntopically, the jejunum and the ileum are adjacent to the greater omentum in front; from behind - to the posterior parietal peritoneum, under which the kidneys, the lower half of the duodenum, the inferior vena cava with the abdominal aorta and their branches are located; from above - to the mesentery of the transverse colon and the intestine itself; on the right - to the blind and ascending colon; on the left - to the descending colon and sigmoid colon; from below, the loops of the small intestine descend into the small pelvis.

Fig. 4. Root of the mesentery of the small intestine and posterior parietal peritoneum

1- transition of the peritoneum to the ascending colon, 2- duodenum (duodenum), 3- right triangular ligament (lig.triangulare dextrum), 4- coronary ligament (lig.coronarium), 5- left triangular ligament (lig.triangulare sinistrum) , 6- phrenic-colonic ligament (lig.phrenicocolicum), 7- attachment of the mesentery of the transverse colon (mesocolon transversum), 8- duodeno-jejunal flexure (flexura duodenojejunalis), 9- transition of the peritoneum to the descending colon, 10- small root intestines (radix mesenterii), 11- attachment of the mesentery of the sigmoid colon (mesocolon sigmoideum)

The ileum passes into the large intestine (intestinum crassum) at the border between the cecum and the ascending colon. Anatomically, it is believed that the ileum flows into the cecum and opens in it with an ileocecal opening (ostium ileocaecale) (Fig. 6). It is an almost horizontal slit, bounded above and below by two folds of the ileal wall, protruding obliquely into the cavity of the cecum, which form the ileocecal valve (valva ileocaecalis, Bauginia's valve), which prevents the retrograde movement of intestinal masses.

Fig. 5. Small intestine and mesenteric vessels

1- transverse colon, 2- pancreas, 3- anastomosis between the middle and left colonic arteries (Reolan's arch), 4- inferior mesenteric vein, 5- inferior mesenteric artery, 6- abdominal aorta, 7-sigmoid arteries and veins, 8 - left common iliac vein, 9 - rectum, 10 - inferior vena cava, 11 - mesentery of the small intestine, 12 - middle colon artery and vein, 13 - paraduodenal pocket

Externally, the terminal ileum passes into the blind almost at a right angle. Therefore, this area, especially in clinical practice, is often called the ileocecal angle or ileocecal junction (Fig. 6, 7).

The peritoneum forms folds and depressions here: the ileo-colon fold (plica ileocolica) limits in front the upper ileocecal cavity (recessus ileocaecalis superior), located between the ileum, its mesentery and the ascending colon; ileocecal fold (plica ileocaecalis), in front of the lower ileocecal cavity (recessus ileocaecalis inferior), located between the ileum, mesentery and cecum. Behind the cecum, in the area of \u200b\u200bthe ileocecal junction, there is a retrocecal pocket (recessus retrocaecalis). Clinical significance of pockets - the possibility of accumulation of pathological exudate of the abdominal cavity, in particular from the right mesenteric sinus or the right lateral canal. In addition, a retrocecal hernia can form in the retrocecal pocket, which is an internal abdominal hernia.

Fig. 6. Ileocecal transition

1- ileocecal opening, 2- Bauginian valve, 3- ascending colon, 4- terminal ileum, 5- opening of the vermiform appendix, 6- appendix, 7- cecum

Blood supply the jejunum and ileum is carried out at the expense of numerous branches of the superior mesenteric artery, extending from the abdominal aorta at the level of the I lumbar vertebra (Fig. 2.5). The superior mesenteric artery, giving off the lower pancreato-duodenal arteries, enters the mesenteric root of the small intestine somewhat to the left of the vein of the same name. From the superior mesenteric artery to the small intestine, there are about 20 jejunal and iliac arteries (aa.jejunales et ileales), and in the area of \u200b\u200bthe ileocecal angle - a large ileo-colon artery (a.ileocolica), supplying the distal ileum, the ileocecal junction , the blind and the initial section of the ascending colon.

Each of the jejunal and iliac arteries is divided into branches that can anastomose with each other. This is how the arterial arches (arcades) of the small intestine are formed, from which the vessels depart, which also form arcades, up to arcades of orders 4-5 (Fig. 8).

Fig. 7. Ileocecal angle

1- folds of the cecum (plicae caecalis), 2- ascending colon (colon ascendens), 3- ileocecal fold (plica ileocaecalis), 4- upper ileocecal cavity (recessus ileocaecalis superior), 5- ileum (ileum), 6- lower ileocecal cavity (recessus ileocaecalis inferior), 7- mesentery of the vermiform appendix (mesoappendix), 8- appendix vermiformis, 9- cecum (caecum), 10- posterior intestinal depression (recessus)

It is fundamentally important to note that from the arcade (marginal artery) closest to the intestinal wall, arteries that have only a forward direction extend to the intestine. They do not anastomose with each other and are involved in the blood supply of only a certain limited area of \u200b\u200bthe intestinal wall.

In bowel operations, ligation of the arcade branches usually does not lead to a violation of the blood supply to the intestinal wall. While ligation of rectal arteries can lead to ischemia and necrosis of the intestinal area. The number of arcades increases from the initial section of the jejunum (1-2) towards the terminal section of the ileum (4-5). The length of straight vessels has an inverse relationship.

Fig. 8. Vascular arcades of the small intestine

1-jejunum, 2- straight vessels, 3- arcades.

During operations, it is important to take into account this peculiarity of the blood supply and to mobilize the necessary section of the intestine the more attentively and gently the closer it is.

Blood outflow from the small intestine through the veins of the same name into the superior mesenteric vein (v. mesenterica superior), and then into the portal vein (v. porta) and then into the liver.

Lymph outflow from the small intestine occurs in numerous mesenteric lymph nodes (nodi lymphatici mesenterici) - nodes of the first order. They are located in the mesentery of the small intestine in several rows, and the largest ones are in its root. It is noted that the central lymph nodes for the jejunum and ileum are several nodes lying near the superior mesenteric vessels in the place where they are covered by the pancreas. From the mesenteric nodes, lymph flows into the lumbar, from the terminal ileum - into the ileal colon, and then along the intestinal trunk (truncus intestinalis) - into the left lumbar trunk (truncus lumbalis sinister) and into the thoracic duct (ductus thoracicus).

In innervation the jejunum and ileum involves the vagus nerve (n. vagus), which has connections with the celiac plexus, and the superior mesenteric plexus (plexus mesentericus superior). The branches of the vagus nerve run in the mesentery along the vessels, providing parasympathetic and sensory innervation. The superior mesenteric plexus is located on the trunk and branches of the corresponding artery. Small internal nerves (nn. Splanchnici minores), which carry sympathetic and sensory fibers from the lower thoracic segments of the spinal cord, are involved in its formation.

1.2. Small intestine physiology

The physiological functions of the small intestine are closely related to its histological structure. The wall of the small intestine consists of 4 layers: the mucous membrane, the submucosa, the muscle layer and the serous membrane (Fig. 9).

The mucous membrane and submucous layer of the intestinal wall form circular (kerkring) folds (Fig. 3.9), increasing its surface area by more than 3 times, which is important for digestion processes. The mucous membrane has a huge number (about 4-5 million) outgrowths - intestinal villi (villi intestinales) (Fig. 9,10). The villi are formed by loose connective tissue covered with intestinal epithelium (Fig. 10). In the center of the villi there is a lymphatic capillary (lactiferous sinus), around which the blood capillaries are located.

Fig. 9. The structure of the wall of the small intestine

1- circular folds, 2- intestinal villi, 3- mucous membrane, 4- submucosa, 5- circular layer of the muscular membrane, 6- longitudinal layer of the muscular membrane, 7- serous membrane.

Enterocytes are represented by a single-layer high columnar epithelium located on the basement membrane. The bulk of epithelial cells are columnar epithelial cells with a striated brush border, which is formed microvilli -outgrowths of the apical plasma membrane of enterocytes. On the surface of the microvilli there is a special layer - the glycocalyx, consisting of lipoproteins and glycosaminoglycans.

The main function of columnar epithelial cells is absorption. The intestinal epithelium contains many goblet cells - unicellular glands that secrete mucus. In addition, the intestinal epithelium contains endocrine cells - endocrinocytes (Kulchitsky cells), which form the hormonal system of the intestine - the APUD system (amine content precursor uptake decarboxilation).

Fig. 10. Diagram of the structure of the intestinal villi

1- intestinal epithelium, 2- central milky sinus, 3- artery, 4- vein, 5- blood capillaries.

In the gaps between the villi on the surface of the epithelium of the entire small intestine, open crypts - intestinal (liberkunovy) glands (glandulae intestinales), formed by a single-layer epithelium, providing the production of intestinal juice. In the lamina propria of the mucous membrane, accumulations of lymphoid nodules - Peyer's patches (noduli lymfoidei aggregati), which are organs of the immune system, are formed.

Submucosal layer is the framework of the intestinal wall and is formed by loose fibrous connective tissue. A network of blood and lymphatic vessels and nerves passes through it. The nerves of the submucosal layer form the Meissner neuro-ganglionic plexus, which, together with the Auerbach plexus of the muscle layer, form the so-called the nervous system of the small intestine... These formations provide innervation of the small intestine, communication with the central nervous system (central nervous system), proper motility and secretory function of the intestine.

Muscular membrane consists of two layers. The inner layer (circular) is thicker than the outer (longitudinal) layer. The nerve (Auerbach) plexus and vessels are located between the muscle layers in the loose connective tissue.

Serous membranerepresented by a single-layer epithelium - the mesothelium, located on the connective tissue subserous basis. The serosa covers the small intestine on all sides and is part of the visceral peritoneum.

The functions of the small intestine are divided into digestive and non-digestive.

Digestive functions are essential for the small intestine and provide the processes of small intestinal digestion: secretory activity, motor activity and absorption.

Non-digestive functions: excretory activity, participation in immune processes, hemostatic, endocrine.

The harmonious APUD system of the small intestine provides endocrine (endocrine) function , involved in the regulation of digestion processes, and other systems of the whole organism.

Digestion - This is a complex physiological process, during which food that has entered the digestive tract undergoes mechanical and chemical transformations, and the nutrients contained in it are absorbed into the blood and lymph after depolymerization.

In the small intestine cavity and parietal (membrane) digestion. In the course of abdominal digestion, hydrolysis (enzymatic decomposition) of polymeric food substrates entering the small intestine to oligomers occurs by enzymes of pancreatic juice and intestinal juice with the participation of bile. Then oligomers are adsorbed on the apical membrane of enterocytes, where parietal digestion is carried out in the glycocalyx layer and on the membrane of microvilli - hydrolysis of oligomers to monomers by intestinal and pancreatic enzymes. Monomeric substrates are absorbed into the blood and lymph through the enterocytes of the intestinal villi. The processes of cavity and parietal hydrolysis occur more intensively in the proximal part of the small intestine. The huge area of \u200b\u200bthe inner surface of the small intestine significantly contributes to hydrolysis, which is ensured by the presence of folds and villi.

All processes of intestinal digestion are regulated by complex neuro-humoral systems, including the central and autonomic intestinal, hormones of the APUD system, and other biologically active substances. The intensity of digestion depends on the activity of the digestive glands, intestinal motility, the nature of the food, the biological state of the enterocyte membranes, etc.

Secretion Is an intracellular process of formation of a specific product of a certain functional purpose (secret) and its release from the glandular cell into the digestive tract. The secretory activity of the small intestine ensures the flow of intestinal juice involved in digestion. Intestinal juice is a cloudy, rather viscous liquid of an alkaline reaction (pH 7.2-8.6), rich in enzymes and mucus, epithelial cells, cholesterol crystals, and salts. The daily clearance of intestinal juice is about 2 liters. Mucus forms a protective layer against excessive mechanical and chemical effects of intestinal chyme. The intestinal juice contains more than 20 digestive enzymes: enterokinase, peptidase (erepsin, etc.), lipase, phospholipase, amylase, lactase, alkaline phosphatase, nuclease, etc. It enhances the intensity of intestinal secretion, primarily, local mechanical and chemical irritation by food masses, hydrolysis products of nutrients, digestive juices.

Motor the activity of the small intestine consists in moving food gruel (chyme) to the large intestine, mechanical processing of food masses, mixing them with digestive juices, maintaining intra-intestinal pressure. The movement of the small intestine is carried out as a result of coordinated contractions of the annular and longitudinal layers of the smooth muscles of the intestinal wall. Types of small bowel contractions: pendulum, peristaltic (very slow, slow, fast, rapid), antiperistaltic and tonic, rhythmic segmentation. Peristaltic movements move the chyme to the colon. The average time for the food chyme to move through the small intestine is 3-4 hours. Usually, peristalsis waves move at a speed of 0.1-3.0 cm / s, and with rapid contractions they reach 7-21 cm / s. In the proximal small intestine, peristalsis is faster than in the distal. With antiperistaltic movements, the chyme moves in the opposite direction, but normally this type of motility is not observed.

Intestinal motor activity is provided by neuro-humoral regulation with significant significance intestinal automatics, i.e. the ability of the intestine to contract independently. From the side of the central nervous system, the hypothalamus, the limbic system, the medulla oblongata, the spinal cord and the cerebral cortex are involved in regulation. The central nervous system has a direct effect on the small intestine through the reflex arcs of the autonomic nerves, which are closed in the submucosa and intermuscular intramural nerve plexuses.

As a rule, parasympathetic innervation (vagus nerve) enhances the motility of the small intestine, and sympathetic (internal nerve) suppresses it. Conditions that cause the predominance or depression of sympathetic or parasympathetic innervation lead to impaired neuro-autonomic regulation of small intestine motility and the development of dynamic small bowel obstruction. It is known that excitement, fear, anger, pain, shock conditions (trauma, blood loss, surgery), intestinal damage, some toxic effects and other causes associated with the activation of the sympathetic system, mainly cause intestinal paresis. And the activation of the vagus (vegetative dystonia, mechanical and chemical irritation of the intestine, etc.) increases peristalsis up to spasm.

The motor activity of the small intestine depends on the physical and chemical properties of the intestinal chyme. Coarse food, vegetable fiber (vegetables), salts, alkalis, non-concentrated acids, hydrolysis products of nutrients increase intestinal peristalsis.

Intestinal motility is affected by humoral substances that act directly on muscle fibers and through receptors on neurons of the intramural nervous system. Serotonin, histamine, gastrin, acetylcholine, etc. activate motility. Catecholamines - adrenaline and norepinephrine - inhibit peristalsis.

Suction -the process of transporting digested food components from the cavity of the gastrointestinal tract to the blood and lymph vessels of the body. Through this process, the body receives the necessary nutrients. Absorption is the final step in intestinal digestion. Absorption through the lymphatic and blood capillaries of the intestinal villi enterocytes is carried out. Micromolecules (monomers of food substrates, water, ions) are mainly transported from the intestinal cavity by a passive method (diffusion, filtration, osmosis) or by an active energy-dependent mechanism. Most of the nutrients are absorbed in the small intestine. The activity of absorption in different parts of the small intestine is selective depending on the type of substrate, but in general it is more intense in the proximal part of the small intestine.

Absorption processes are controlled by neuro-humoral mechanisms by analogy with other digestive functions of the small intestine. The activity of the parasympathetic nervous system increases the absorption, in particular of water, carbohydrates and fats, and inhibits the sympathetic. Impaired absorption (malabsorption) leads to a deficiency of plastic and energy substances, vitamins and microelements, water-electrolyte imbalance.

Small intestine

Intestinumtenue (gr. enter on, hence the inflammation of the intestinal mucosa - enteritis), the small intestine, begins at the pylorus and, having formed on its way a whole series of loop-like bends, ends at the beginning of the large intestine. The length of the small intestine in the corpses of men is about 7 m, in women - about 6.5 m, and it exceeds the body length by 4.3 times. Due to posthumous relaxation of the musculature, it is always longer on corpses than on a living one. In the small intestine, mechanical (advancement) and further chemical processing of food takes place under conditions of an alkaline reaction, as well as the absorption of nutrients. Accordingly, there are special devices for the secretion of digestive juices (glands located both in the intestinal wall and outside it) and for the absorption of digested substances.

The small intestine is divided into three sections: 1) duodenum, duodenum, the section closest to the stomach, 25-30 cm long: 2) jejunum jejunum, which accounts for 2/5 of the small intestine minus duodenum, and 3) ileum, ileum , - the remaining 3/5. This conditional distinction between the jejunum and the ileum is accepted, since there is no definite anatomical border between them.

Duodenum, duodenum, bends like a horseshoe around the head of the pancreas. Four main parts are distinguished in it: 1) pars superior is directed at level I of the lumbar vertebra to the right and back and, forming a downward bend, flexura duodeni superior, turns into 2) pars descendens, which descends, located to the right of the spinal column, to the III lumbar vertebra ; here the second turn occurs, flexura duodeni inferior, and the intestine is directed to the left and forms 3) pars horizontalis (interior), going transversely in front of v. cava inferior and aorta, and 4) pars ascendetis, rising to the level of I-II of the lumbar vertebra on the left and in front.

Duodenal topography... On its way, the duodenum with the inner side of its bend grows together with the head of the pancreas; in addition, pars superior is in contact with the square lobe of the liver, pars descendens - the right kidney, pars horizontalis passes between a. and v. mesentericae superiores in front and aorta and v. cava inferior - behind. Duodenum has no mesentery and is only partially covered by the peritoneum, mainly in front. The relation to the peritoneum of the area closest to the pylorus (over about 2.5 cm) is the same as that of the outlet of the stomach. The anterior surface of the pars descendens remains uncovered by the peritoneum in its middle section, where the pars descendens is intersected in front by the root of the mesentery of the transverse colon; pars horizontalis is covered with the peritoneum in front, with the exception of a small area where the duodenum is crossed by the mesentery root of the small intestine, enclosing vasa mesenterica superiores.

With the transition of pars ascendens duodeni into the jejunum on the left side of the I or, more often, II of the lumbar vertebra, a sharp bend of the intestinal tube, flexura duodenojejunalis, is obtained, and the initial part of the jejunum goes down, forward and left. Flexura duodenojejunalis, due to its fixation on the left side of the II lumbar vertebra, serves as an identification point during surgery for finding the beginning of the jejunum.

Duodenum a living person. X-ray examination (Fig. 132) the initial part of the duodenum is allocated in a special section - the bulb, bulbus duodeni.

It has the form of a triangular shadow, the base turned towards the gatekeeper, from which, at the moment of contraction of the latter, the shadow of the bulb is separated by an enlightenment corresponding to the shortened gatekeeper. The diameter of the bulb is larger than that of the rest of the duodenum. Its radiological boundaries: from enlightenment in the place of the gatekeeper to the apex of its triangular shadow, and on the corpse - from valvula pylori to the first circular fold of the mucous membrane. The mucous bulb, as in the pylorus, has longitudinal folds, while in the rest of the duodeni the folds are circular.

These features of the structure of the bulb are associated with the fact that bulbus duodeni does not develop from the middle intestine, like the entire duodenum, but from the front.

The shape and position of the duodenum in a living person is extremely variable. There are three options for the shape and position:

1. Duodenum in the form of a horseshoe, positioned as on a corpse; while all 4 parts of it are expressed.

2. Duodenum in the form of a sharply curved loop located vertically; in this case, due to the sharp bend and vertical position, only pars descendens and pars ascendens are obtained.

3. Duodenum in the form of a steeply curved loop located frontally. Due to the sharp bend and horizontal position, only pars superior and pars horisontalis differ. Transitional forms are observed between the three options.

The variety of shapes and positions of the duodenum is due to the different degree of fixation of the duodeni to the abdominal wall (sometimes there is even a small mesentery in the initial part) and the mobility of the stomach. There are also a number of options for the development and position of duodeni: 1) situs inversus partialis duodeni - the position of the duodenum is a mirror image of its normal topic; 2) duodenum mobile - an elongated and mobile duodenum folds into loops; 3) inversio duodeni - the descending part does not go down, but rises up and to the left, forming the letter P. All these variations and anomalies of the form and position of the duodeni have been studied only thanks to the X-rays.

Lean and ileum... The jejunum and ileum are united under the general name intestinum tenue mesenteriale, since this entire section, unlike the duodenum, is completely covered by the peritoneum and is attached to the posterior abdominal wall through the mesentery. Although there is no pronounced border between the intestinum jejunum, the jejunum (the name comes from the fact that this section is usually empty on the corpse), and the intestinum ileum, the ileum, there is no, as indicated above, however, the typical parts of both sections (the upper part of jejunum and the lower part - ileum) have clear differences: jejunum has a larger diameter, its wall is thicker, it is richer with vessels (the differences from the mucous membrane will be indicated below). The loops of the mesenteric part of the small intestine are located mainly in the mesogastrium and hypogastrium. In this case, the loops of the jejunum lie mainly to the left of the midline, while the loops of the ileum lie mainly to the right of the midline. The mesenteric part of the small intestine is covered in front on a greater or lesser extent by an omentum (serous peritoneal cover descending here from the greater curvature of the stomach). It lies, as it were, in a frame formed from above by the transverse colon, from the sides - ascending and descending, at the bottom of the loop of the intestine can descend into the small pelvis; sometimes part of the loops is located in front of the colon. In approximately 2% of cases, a process - diverticulum Meckelii (the remainder of a part of the embryonic vitelline duct) is found on the ileum at a distance of about 1 m from its end. The process is 5-7 cm long, approximately the same caliber as the ileum, and extends from the side opposite to the mesentery attachment to the intestine.

Structure... The mucous membrane, tunica mucosa, of the small intestine has a matte, velvety appearance from the numerous intestinal villi covering it, villi intestinales (Fig. 133).

The villi are processes of the mucous membrane about 1 mm long, covered, like the latter, with a cylindrical epithelium and have a lymphatic sinus and blood vessels in the center. The function of the villi is to absorb nutrients exposed to the intestinal juice secreted by the intestinal glands; at the same time, proteins and carbohydrates are absorbed through the venous vessels and undergo liver control, and fats - through the lymphatic (milk). The number of villi is greatest in the jejunum, where they are thinner and longer. In addition to digestion in the intestinal cavity, there is a recently discovered parietal digestion. It takes place in the smallest villi, visible only under an electron microscope and containing digestive enzymes.

The absorption area of \u200b\u200bthe mucous membrane of the small intestine is significantly increased due to the presence of transverse folds in it, called circular folds, plicae circilares (Fig. 134).

These folds consist only of mucous and submucosal membranes (tunica muscularis does not participate in them) and are permanent formations that do not disappear even when the intestinal tube is stretched. Circular folds are not the same in all parts of the small intestine.

In addition to circular folds, on the mucous membrane of the duodenum there is longitudinal folding at the very beginning of it (in the bulbus region) and longitudinal plica longitudinalis duodeni, located on the medial wall of the descending part; plica longitudinalis duodeni looks like a roller and ends with a papilla, papilla duodeni major (see Fig. 134). On papilla duodeni major, the bile duct of the liver and the excretory duct of the pancreas open with one common opening. This explains the name of the expansion (ampoule) immediately before the outlet of the duct, ampulla hepatopancreatica. Proximal to the papilla duodeni major is the second smaller papilla - papilla duodeni minor (an accessory pancreatic duct opens on it) (see Fig. 134).

Along the entire length of the small intestine, as well as, as will be indicated below, and the colon are located in the mucous membrane, not going into the submucosa, numerous small simple tubular glands, glandulae intestinales; they separate the intestinal juice. In the duodenum, mainly in its upper half, there is another type of gland, glandulae duodendles, which, unlike glandulae intestinales, are located in the submucosa. In structure, they are similar to the pyloric glands of the stomach. In the small intestine there is a lymphatic apparatus that serves to neutralize harmful substances and microorganisms. It is represented by single (solitary) follicles, folliculi lymphatici solitarii, and their clusters, folliculi lymphatici aggregati (Peyeri), also called Peyer's patches.

Folliculi lymphatici solitarii are scattered throughout the gut in the form of whitish eminences the size of a grain of millet (Fig. 135).

Folliculi lymphatici aggregati are found only in the ileum. They have the form of flat oblong plaques, the longitudinal diameter of which coincides with the longitudinal axis of the intestine. They are located on the side opposite to the place of mesentery attachment to the intestine.

The total number of Peyer's patches is 20-30. In the lymphatic apparatus of the small intestine, biological (intracellular) digestion of food is also carried out.
The muscular membrane, tunica muscularis, according to the tubular shape of the small intestine, consists of two layers of smooth fibers: outer - longitudinal and inner - circular; the circular layer is better developed than the longitudinal one; the muscular layer becomes thinner towards the lower end of the intestine. There is a view according to which, in addition to the longitudinal and circular layers of the muscles, in the last (circular) layer there are spiral muscle fibers, which in places form a continuous layer of spiral muscles (Brandt, Carrey). Contractions of muscle fibers are peristaltic in nature, they consistently spread towards the lower end, with circular fibers narrowing the lumen, and longitudinal, shortening, contribute to its expansion (distally from the contracted ring of fibers). Coiled fibers promote peristaltic wave propagation distally along the axis of the intestinal tube. Contractions in the opposite direction are called antiperistaltic.

The serous membrane, tunica serosa, covering the small intestine from all sides, leaves only a narrow strip behind, between the two sheets of the mesentery, between which nerves, blood and lymphatic vessels approach the intestine.

The jejunum and ileum of a living person... On X-ray examination, shadows of the loops of the small intestines are visible. The loops of the jejunum are located partly horizontally, partly vertically, on the left and in the middle of the abdominal cavity.

The loops of the ileum are located in the area of \u200b\u200bthe right iliac fossa and are more often vertical and oblique, forming a conglomerate.

Relief of the mucous membrane. In the jejunum, the transverse folds give the outer contours of the shadow a scalloped or feathery character, which is a characteristic feature of the small intestine; in certain phases of peristalsis, thanks to the autoplasty apparatus, as in the stomach, both longitudinal and oblique folds are observed. In the ileum, as the colon approaches the colon, the number of longitudinal folds increases. Transverse folds - anatomical, permanent; the rest of the folds are physiological, non-permanent.

Longitudinal folds form grooves and channels for the passage of food, and transverse folds somewhat delay its advance. Due to the movement of all these folds, a variety of X-ray pictures are obtained.

The flow of food from the small intestine into the cecum is rhythmic and regulated by the valva ileocecalis located in the cecum, which opens and closes like a gatekeeper. The contrast food taken in 1/2 hour enters the jejunum, after 1.5 hours it fills the ileum, after 4 hours it begins to enter the cecum and after 7-8 hours it completely passes into the colon.

Small intestine arteries, aa. infestinales jejunales et ilei, come from a. mesenterica superior. Duodenum is powered by aa. pancreaticoduodenals superiores (from a. gastroduodenalis) and from aa. pancreaticoduodenales inferiores (from a. mesenterica superior). Venous blood flows through single-shift veins into v. portae. Lymphatic vessels carry lymph in nodi lymphatici celiaci et mesenterici (see the section on the lymphatic system).

Innervation is from the autonomic nervous system. There are three nerve plexuses in the intestinal wall: the sub-serous, plexus subserosus, intermuscular, plexus myentericus, and the submucosal, plexus submucosus.

The feeling of pain is transmitted along the sympathetic pathways; peristalsis and secretion decreases. N. vagus enhances peristalsis and secretion.