The jejunum and ileum are combined under common name intestinum tenue mesenterial, since this entire section, unlike duodenum, is completely covered with peritoneum and is attached to the posterior abdominal wall through the mesentery. Although there is no clearly defined boundary between the intestinum jejunum (jejunum) (the name comes from the fact that on a corpse this section is usually empty) and the intestinum ileum (ileum), there are typical parts of both sections ( top part jejunum and lower - ileum) have clear differences: the jejunum has a larger diameter, its wall is thicker, it is richer in blood vessels (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 for a greater or lesser extent by the omentum (serous peritoneal covering descending here from the greater curvature of the stomach). It lies, as it were, in a frame formed on top of a transverse colon, from the sides - ascending and descending, at the bottom the intestinal loops can descend into the pelvis; sometimes part of the loops is located in front of the colon. In approximately 2% of cases, a process is found on the ileum at a distance of about 1 cm from its end - Meckel's diverticulum (diverticulum Meckelii) (the remnant of part of the embryonic vitelline duct). The process is 5-7 cm long, approximately the same caliber as the ileum and extends from the side opposite to the attachment of the mesentery to the intestine.
Mixing the chyme.
Emulsification of fats by bile.
Digestion of fats, proteins and carbohydrates under the influence of enzymes contained in intestinal and pancreatic juices.
Suction nutrients, vitamins and mineral salts.
Bactericidal treatment of food due to lymphoid formations of the mucous membrane.
Evacuation of undigested substances into the large intestine.
Structure.
1. The mucous membrane (tunica mucos) of the small intestine has many intestinal villi (villi intestinales). The villi are processes of the mucous membrane about 1 mm long, covered, like the latter, with columnar epithelium and in the center have a lymphatic sinus and blood vessels. The function of the villi is to absorb nutrients exposed to intestinal juice secreted by the intestinal glands; in this case, proteins and carbohydrates are absorbed through the venous vessels and are controlled by the liver, and fats through the lymphatic (lacteal) vessels. 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 parietal digestion. It occurs in the smallest fibers, visible only under electron microscope and containing digestive enzymes.
Absorption area of the mucous membrane small intestine significantly enlarged due to the presence of transverse folds in it, called circular folds (plicae circuldres). These folds consist only of the mucous and submucosal membranes.
The small intestine contains 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 aggregate) (Peyeri), also called Peyer's patches.
The lymphatic apparatus of the small intestine also carries out biological (intracellular) digestion of food.
Enlarged intestinal lymph nodes - mesodenitis.
2. The muscular layer (tunica musculdri), corresponding to the tubular shape of the small intestine, consists of two layers of smooth fibers: the outer - longitudinal and the inner - circular; the circular layer is better developed than the longitudinal one; the muscular layer towards the lower end of the intestine becomes thinner. Contractions of muscle fibers determine 4 types of movements:
1. peristaltic nature.
2. antiperistaltic.
3.Rhythmic
3. The serous membrane (tunica serosa), covering the small intestine on all sides, leaves only a narrow strip at the back, between the two layers of the mesentery, between which nerves, blood and lymphatic vessels approach the intestine.
And the ileum. Like other parts of the small intestine, the jejunum consists of the following layers:
formed from epithelium, lamina propria and muscularis lamina mucosa (MPL);
and Lieberkühn's crypts (LC) are well developed. Leaf-shaped villi are the most common form. The mucous membrane forms many long circular folds (not shown in the figure);
- loose layer connective tissue, rich blood vessels and nerves, with bundles of collagen fibers crossing each other at an angle of 70°, as in other parts of the small intestine;
consists of an internal circular (IC) and external longitudinal (LP) layers of smooth muscle cells with a nerve plexus (NS) located between them;
- a layer of loose connective tissue that attaches the peritoneum to the muscular layer;
- This is the visceral peritoneal (peritoneal) mesothelium that envelops the jejunum.
Jejunum and other portions of the small intestine (except for a short portion of the duodenum) are attached to the dorsal wall of the abdominal cavity by the mesentery. This is a thin sheet of connective tissue, covered on both sides by the peritoneum, which continues with the visceral layer of the serous membrane.
In the figure, the mesentery's attachment to the jejunum is cut and expanded to show the branching of arteries (A), nerve fibers (HB), and the collecting lymphatic vessel (CL) in the wall of the jejunum.
Entering the wall of the small intestine at almost the same distance from each other, small muscular arteries (A) give off several branches to supply the subserosal base and then form a large muscular plexus (MS).
This plexus communicates with the submucosal choroid plexus (SCP), from which arterioles ascend to the mucous membrane that supplies the intestinal villi and Lieberkühn glands.
Veins follow the branching of arteries, so their description is omitted.
The nerve fibers form two plexuses: the myenteric plexus (MCP), located between the two layers of the muscularis propria, and the submucosal plexus (not shown) in the submucosa. The first plexus is responsible for controlling the peristalsis of the small intestine, and the second is involved in the innervation of the mucous membrane.
The initial lymphatic capillaries of the small intestine - the lacteal vessels (MLVs) form a capillary network around the intestinal glands, constituting the mucosal lymphatic plexus (MLP). From this plexus, lymph flows to the submucosal lymphatic plexus (SLP), then reaches the muscular lymphatic plexus (MLP), located between the two muscle layers muscle membrane. Through collector lymphatic vessels (LVVs), lymph reaches regional lymph nodes.
Skinny and ileum. The jejunum and ileum are combined under the general name intestinum tenue mesenteriale, since this entire section, unlike the duodenum, is completely covered with peritoneum and is attached to the posterior abdominal wall through the mesentery. Although there is no clearly defined boundary between the jejunum, the jejunum (the name comes from the fact that on a corpse this section is usually empty), and the ileum, the ileum, as indicated above, the typical parts of both sections (the upper part of the jejunum and lower - ileum) have clear differences: the jejunum has a larger diameter, its wall is thicker, it is richer in blood vessels (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, with the loops of the jejunum lying mainly to the left of the midline, the loops of the ileum - mainly to the right of the midline. The mesenteric part of the small intestine is covered in front for a greater or lesser extent by the omentum (serous peritoneal covering descending here from the greater curvature of the stomach). It lies, as it were, in a frame formed by the transverse colon on top, ascending and descending on the sides, and at the bottom the loops 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 is found on the ileum, at a distance of about 1 m from its end - diverticulum Meckelii (the remnant of part of the embryonic vitelline duct). The process is 5-7 cm long, approximately the same caliber as the ileum and extends from the side opposite to the attachment of the mesentery to the intestine.
Structure. The mucous membrane, tunica mucosa, of the small intestine has a matte, velvety appearance due to the numerous intestinal villi, villi intestinales, covering it. The villi are processes of the mucous membrane about 1 mm long, covered, like the latter, with columnar epithelium and in the center have a lymphatic sinus and blood capillaries.
The function of the villi is the absorption of nutrients exposed to bile, pancreatic and intestinal juice secreted by the intestinal glands; while proteins and carbohydrates are absorbed through venous vessels and are controlled by the liver, and fats are controlled by the lymphatics. 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 parietal digestion. It occurs in microvilli, visible only under an electron microscope and containing digestive enzymes.
The absorptive area of the mucous membrane of the small intestine is significantly increased due to the presence of transverse folds in it, called circular folds, plicae circulares. These folds consist only of the mucous membrane and submucosa (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 of the same nature in all parts of the small intestine. In addition to circular folds, the mucous membrane of the duodenum has longitudinal folding at the very beginning, in the ampulla (bulbus) region, and longitudinal plica longitudinalis duodeni, located on the medial wall of the descending part; plica longitudinalis duodeni has the appearance of a ridge and ends with a papilla, papilla duodeni major.
On papilla duodeni major, the bile duct of the liver and excretory duct pancreas. This explains the name of the expansion (ampull) immediately in front of the outlet of the duct - ampulla hepatopancreatica. Proximal to papilla duodeni major there is a second papilla of smaller size - papilla duodeni minor (the accessory duct of the pancreas opens on it). Throughout the entire length of the small intestine, and also, as will be indicated below, the large intestine, numerous small simple tubular glands, glandulae intestinales, are located in the mucous membrane, without entering the submucosa; they secrete intestinal juice.
IN duodenum, mainly in its upper half, there is another type of gland - glandulae duodenales, which, unlike glandulae intestinales, are located in the submucosa. They are similar in structure to the pyloric glands of the stomach. The small intestine contains a lymphatic apparatus that serves to neutralize harmful substances and microorganisms. It is represented by single follicles, folliculi lymphatici solitarii, and their clusters - group lymphatic follicles, folliculi lymphatici aggregati.
Folliculi lymphatici solitarii are scattered throughout the small intestine in the form of whitish elevations the size of millet grains. Folliculi lymphatici aggregati are present only in the ileum. They have the appearance of flat oblong plaques, the longitudinal diameter of which coincides with longitudinal axis intestines. They are located on the side opposite to the place where the mesentery attaches to the intestine. Total group lymphatic follicles 20-30. The lymphatic apparatus of the small intestine also carries out biological (intracellular) digestion of food.
The muscular layer, tunica muscularis, corresponding to the tubular shape of the small intestine, consists of two layers of myocytes: the outer - longitudinal and the inner - circular; the circular layer is better developed than the longitudinal one; the muscular layer towards the lower end of the intestine becomes thinner. There is a view according to which, in addition to the longitudinal and circular layers of muscle, the last (circular) layer contains spiral muscle fibers, in some places forming a continuous layer of spiral muscle.
Contractions of muscle fibers are peristaltic in nature; they sequentially spread towards the lower end, with circular fibers narrowing the lumen, and longitudinal fibers, shortening, promoting its expansion (distal from the contracted ring of fibers). The spiral fibers promote the propagation of the peristaltic wave 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 on all sides, leaves only a narrow strip at the back, between the two layers of the mesentery, between which nerves, blood and lymphatic vessels approach the intestine.
X-ray anatomy of the jejunum and ileum. At x-ray examination shadows of loops of small intestines are visible. The loops of the jejunum are located partly horizontally, partly vertically, on the left and in the middle abdominal cavity. The loops of the ileum are located in the area of the right iliac fossa and are often vertical and oblique, forming a conglomerate. Relief of the mucous membrane. In the jejunum, transverse folds give the outer contours of the shadow a scalloped or feathery character, which is characteristic feature small intestine; in certain phases of peristalsis, as in the stomach, the formation of longitudinal and oblique folds is observed. In the ileum, as it approaches the colon, the number of longitudinal folds increases. Longitudinal folds form grooves and channels for the passage of food, while transverse folds somewhat delay its movement.
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 caecum occurs rhythmically and is regulated by the valva ileocaecalis, located in the caecum, which opens and closes like a pylorus. The received contrast mass enters the jejunum after 1/2 hour, fills the ileum after 1-2 hours, begins to enter the caecum after 4 hours and completely passes into the colon after 7-8 hours.
Arteries of the small intestine, aa. intestinales jejunales et ileales, come from a. mesenterica superior Duodenum feeds from aa. pancreaticoduodenals superiores (from a. gastroduodenahs) and from aa pancreaticoduodenals inferiores (from a. mesenterica superior). Venous blood flows through the veins of the same name into v. portae. Lymphatic vessels carry lymph to the nodi lymphatici coeliaci et mesenterici. Innervation from the autonomic nervous system. There are three nerve plexuses in the intestinal wall: the subserous plexus, plexus subserosus, the musculoenteric plexus, plexus myentericus, and the submucosal plexus, plexus submucosus. The feeling of pain is transmitted through the sympathetic pathways; peristalsis and secretion decrease. N. vagus enhances peristalsis and secretion.
Jejunum, jejunum and ileum, ileum, - are contained in the middle and lower parts of the abdominal cavity, they are covered with peritoneum on all sides (intraperitoneal) and have a mesentery, mesenterium. The initial part of the jejunum is inactive due to the short mesentery and fixation of the duodenum-empty flexure. The loops of the jejunum are located horizontally in the upper left part of the lower floor of the abdominal cavity and in the umbilical region, regio umbilicalis. The loops of the ileum are located vertically in the abdomen, regio hypogastricum, right iliac fossa and pelvic cavity. The distal segment of the ileum flows into the. Approximately at a distance of 1 m from its end there may be a process 5-7 cm long - diverticulum of the ileum (Meckel), diverticulum ilei (Meckeli), - congenital anomaly, which occurs in 2% of individuals (Richard M. Mendelson, 1996) and leads to acute inflammation, melena, and volvulus. The loops of the small intestine are covered in front by the omentum; on the right - ascending; from above - transverse, from the left - descending colon. At the back, the loops of the empty intestine and ileum are adjacent to the parietal peritoneum. On the left and below, the loops of the small intestine are adjacent to, and in the pelvic cavity - to bladder, rectum in men, and in women - to the uterus. The empty intestine is distinguished from the ileum by the following signs: it has a larger diameter (4-6 cm) than the ileum - (3-3.5 cm). The wall of the jejunum is thicker, its color is redder, the mucous membrane forms more folds and villi.
The structure of the small intestine. The wall of the small intestine consists of four layers:
- Mucous, tunica mucosa;
- Submucosa, tela submucosa;
- Muscular, tunica muslularis;
- Serous, tunica serosa.
Mucous membrane, tunica mucosa, - is formed by a single-layer cylindrical and prismatic epithelium, submucosa and muscular plate. The relief of the mucous membrane has a characteristic velvety appearance. This is due to the presence of circular folds, intestinal villi and crypts. There are about 650-700 folds in the small intestine; their length reaches 5 cm, height - 8 mm. In addition to the circular folds, there is a longitudinal fold, plica longitudinalis duodeni, which originates on the left wall of the descending part and ends with the major papilla (Vateri), papilla duodeni major (Vateri). On it, one common opening opens the joint bile and pancreatic duct. This is a landmark difference in surgical practice.
Intestinal villi, villi intestinales, is a finger-shaped protrusion of the mucous membrane without a submucosa. IN small intestine there are about 4-5 million of them. The main purpose is to absorb proteins, fats, carbohydrates and increase the absorptive and secretory surfaces of the small intestine. In the duodenum and jejunum there can be 30-40 of them per 1 mm2. Each villus contains blood and lymphatic vessels that form vascular networks, as well as nerves. The activity of the villi is regulated by the action of the hormone villikinin.
The surface of the villi is covered with a single-layer columnar epithelium, in which three types of cells are distinguished: intestinal epithelial cells with a striated border, goblet cells (enterocytes), which produce mucus, and a small number of enteroendocrine cells.
The role of microvilli is not limited to this - a large number of active enzymes involved in the breakdown (parietal digestion) and absorption of nutrients have been found in them. Intestinal crypts, or glands, cryptae intestinales sen glandulae Lieberkuchni, are tubular depressions of the epithelium in their own layer of the mucous membrane. Their length reaches 0.5 mm; There are up to 100 crypts per 1 mm2. Most of them are found in the duodenum and jejunum, less in the ileum. The total area of the crypts in the small intestine is 14 m2. food that enters the small intestine undergoes digestive action not only in the intestinal cavity, but also between the microvilli and in the crypts. In the submucosa of the mucous membrane, accumulations of lymphoid tissue form single noduli lymphoidei solitarii and crowded lymphoid nodules [follicles], lymphoidei noduli aggregati (Peyeri).
Single follicles are distributed evenly along the entire length of the small intestine, their diameter ranges from 0.5 to 3 mm. Crowded follicles have a length of 2 to 12 cm, a width of 1-3 cm and are contained in the mucous membrane of the ileum opposite the attachment of the mesentery. Total number of crowded lymphoid follicles ranges from 20 to 30.
Submucosa, tela submucosa, duodenum and initial part of the jejunum contains a large number of tubular branched duodenal glands, glandulae duodenalis, producing intestinal juice. Along with this, the small intestine contains a large number of simple tubular intestinal glands, glandulae intestinales, which produce intestinal juice and mucus. In addition, in the formation of intestinal juice important role play by the large digestive glands - the liver and pancreas.
Muscularis, tunica muscularis, - consists of longitudinal and circular smooth muscle fibers. The circular layer is developed. Between the layers there is a layer of unformed connective tissue, in which the vascular networks and nerve plexus pass. Main function muscular membrane - mixing food in the intestinal lumen and pushing it in the distal direction. This is achieved through the longitudinal and circular layers of the intestinal wall. The bundles of smooth muscle fibers of both layers are oriented in a spiral manner and carry out two types of movements: pendulum-like - due to alternating rhythmic contractions of the longitudinal and circular layers; peristaltic - due to coordinated contractions of both layers.
Serosa, tunica serosa, is a visceral layer of the peritoneum, covering the empty and ileum on all sides and forms the mesentery, mesenterium.
Jejunum and ileum. The jejunum and ileum are combined under the general name intestinum tenue mesenteriale, since this entire section, unlike the duodenum, is completely covered with peritoneum and is attached to the posterior abdominal wall through the mesentery. Although there is no clearly defined boundary between the jejunum, the jejunum (the name comes from the fact that on a corpse this section is usually empty), and the ileum, the ileum, as indicated above, the typical parts of both sections (the upper part of the jejunum and lower - ileum) have clear differences: the jejunum has a larger diameter, its wall is thicker, it is richer in blood vessels (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, with the loops of the jejunum lying mainly to the left of the midline, the loops of the ileum - mainly to the right of the midline. The mesenteric part of the small intestine is covered in front for a greater or lesser extent by the omentum (serous peritoneal covering descending here from the greater curvature of the stomach). It lies, as it were, in a frame formed by the transverse colon on top, ascending and descending on the sides, and at the bottom the loops 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 is found on the ileum, at a distance of about 1 m from its end - diverticulum Meckelii (the remnant of part of the embryonic vitelline duct). The process is 5-7 cm long, approximately the same caliber as the ileum and extends from the side opposite to the attachment of the mesentery to the intestine.
Structure. The mucous membrane, tunica mucosa, of the small intestine has a matte, velvety appearance due to the numerous intestinal villi, villi intestinales, covering it. The villi are processes of the mucous membrane about 1 mm long, covered, like the latter, with columnar epithelium and in the center have a lymphatic sinus and blood capillaries.
The function of the villi is the absorption of nutrients exposed to bile, pancreatic and intestinal juice secreted by the intestinal glands; in this case, proteins and carbohydrates are absorbed through the venous vessels and are controlled by the liver, and fats through the lymphatic vessels. 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 parietal digestion. It occurs in microvilli, visible only under an electron microscope and containing digestive enzymes.
The absorptive area of the mucous membrane of the small intestine is significantly increased due to the presence of transverse folds in it, called circular folds, plicae circulares. These folds consist only of the mucous membrane and submucosa (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 of the same nature in all parts of the small intestine. In addition to circular folds, the mucous membrane of the duodenum has longitudinal folding at the very beginning, in the ampulla (bulbus) region, and longitudinal plica longitudinalis duodeni, located on the medial wall of the descending part; plica longitudinalis duodeni has the appearance of a ridge and ends with a papilla, papilla duodeni major.
In papilla duodeni major, the bile duct of the liver and the excretory duct of the pancreas open through one common opening. This explains the name of the expansion (ampull) immediately in front of the outlet of the duct - ampulla hepatopancreatica. Proximal to papilla duodeni major there is a second papilla of smaller size - papilla duodeni minor (the accessory duct of the pancreas opens on it). Throughout the entire length of the small intestine, and also, as will be indicated below, the large intestine, numerous small simple tubular glands, glandulae intestinales, are located in the mucous membrane, without entering the submucosa; they secrete intestinal juice.
In the duodenum, mainly in its upper half, there is another type of gland - glandulae duodenales, which, unlike glandulae intestinales, are located in the submucosa. They are similar in structure to the pyloric glands of the stomach. The small intestine contains a lymphatic apparatus that serves to neutralize harmful substances and microorganisms. It is represented by single follicles, folliculi lymphatici solitarii, and their clusters - group lymphatic follicles, folliculi lymphatici aggregati.
Folliculi lymphatici solitarii are scattered throughout the small intestine in the form of whitish elevations the size of millet grains. Folliculi lymphatici aggregati are present only in the ileum. They have the appearance 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 where the mesentery attaches to the intestine. The total number of group lymphatic follicles is 20-30. The lymphatic apparatus of the small intestine also carries out biological (intracellular) digestion of food.
The muscular layer, tunica muscularis, corresponding to the tubular shape of the small intestine, consists of two layers of myocytes: the outer - longitudinal and the inner - circular; the circular layer is better developed than the longitudinal one; the muscular layer towards the lower end of the intestine becomes thinner. There is a view according to which, in addition to the longitudinal and circular layers of muscle, the last (circular) layer contains spiral muscle fibers, in some places forming a continuous layer of spiral muscle.
Contractions of muscle fibers are peristaltic in nature; they sequentially spread towards the lower end, with circular fibers narrowing the lumen, and longitudinal fibers, shortening, promoting its expansion (distal from the contracted ring of fibers). The spiral fibers promote the propagation of the peristaltic wave 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 on all sides, leaves only a narrow strip at the back, between the two layers of the mesentery, between which nerves, blood and lymphatic vessels approach the intestine.
X-ray anatomy of the jejunum and ileum. X-ray examination reveals shadows of small intestinal loops. 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 the right iliac fossa and are often vertical and oblique, forming a conglomerate. Relief of the mucous membrane. In the jejunum, 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, as in the stomach, the formation of longitudinal and oblique folds is observed. In the ileum, as it approaches the colon, the number of longitudinal folds increases. Longitudinal folds form grooves and channels for the passage of food, while transverse folds somewhat delay its movement.
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 caecum occurs rhythmically and is regulated by the valva ileocaecalis, located in the caecum, which opens and closes like a pylorus. The received contrast mass enters the jejunum after 1/2 hour, fills the ileum after 1-2 hours, begins to enter the caecum after 4 hours and completely passes into the colon after 7-8 hours.
Arteries of the small intestine, aa. intestinales jejunales et ileales, come from a. mesenterica superior Duodenum feeds from aa. pancreaticoduodenals superiores (from a. gastroduodenahs) and from aa pancreaticoduodenals inferiores (from a. mesenterica superior). Venous blood flows through the veins of the same name into v. portae. Lymphatic vessels carry lymph to the nodi lymphatici coeliaci et mesenterici. Innervation from the autonomic nervous system. There are three nerve plexuses in the intestinal wall: the subserous plexus, plexus subserosus, the musculoenteric plexus, plexus myentericus, and the submucosal plexus, plexus submucosus. The feeling of pain is transmitted through the sympathetic pathways; peristalsis and secretion decrease. N. vagus enhances peristalsis and secretion.
