Jejunum functions. Jejunum Why is the jejunum shorter than the ileum?
The small intestine is located between the stomach and the cecum and is the largest section of the digestive system. The main function of the small intestine is the chemical processing of the bolus of food (chyme) and the absorption of the products of its digestion.
Structure
The small intestine is a very long (2 to 5 m) hollow tube. It starts from the stomach and ends in the ileocecal angle, at the point of its connection with the cecum. Anatomically, the small intestine is conventionally divided into three sections:
1. Duodenum. It is located in the back of the abdominal cavity and is shaped like the letter “C”;
2. Jejunum. Located in the middle part of the abdominal cavity. Its loops lie very freely, covered with peritoneum on all sides. This intestine got its name because when autopsying corpses, pathologists almost always find it empty;
3. Ileum - located in the lower part of the abdominal cavity. It differs from other parts of the small intestine in having thicker walls, better blood supply and a larger diameter.
Digestion in the small intestine
The food mass passes through the small intestine in about four hours. During this time, the nutrients contained in the food continue to be broken down by enzymes in the intestinal juice into smaller components. Digestion in the small intestine also involves active absorption of nutrients. Inside its cavity, the mucous membrane forms numerous outgrowths and villi, which significantly increases the absorption surface area. So in adults, the area of the small intestine is at least 16.5 square meters.
Functions of the small intestine
Like any other organ in the human body, the small intestine performs not one, but several functions. Let's look at them in more detail:
- The secretory function of the small intestine is the production by the cells of its mucous membrane of intestinal juice, which contains enzymes such as alkaline phosphatase, disaccharidase, lipase, cathepsins, peptidase. All of them decompose the nutrients contained in chyme into simpler ones (proteins into amino acids, fats into water and fatty acids, and carbohydrates into monosaccharides). An adult secretes approximately two liters of intestinal juice per day. It contains a large amount of mucus, which protects the walls of the small intestine from self-digestion;
- Digestive function. Digestion in the small intestine involves the breakdown of nutrients and their further absorption. Thanks to this, only indigestible and indigestible foods enter the colon.
- Endocrine function. In the walls of the small intestine there are special cells that produce peptide hormones, which not only regulate intestinal function, but also affect other internal organs of the human body. Most of these cells are located in the duodenum;
- Motor function. Due to the longitudinal and circular muscles, wave-like contractions of the walls of the small intestine occur, pushing the chyme forward.
Diseases of the small intestine
All diseases of the small intestine have similar symptoms and are manifested by abdominal pain, flatulence, rumbling, and diarrhea. Stool occurs several times a day, profusely, with the remains of undigested food and a large amount of mucus. Blood in it is observed extremely rarely.
Among diseases of the small intestine, inflammation is most often observed - enteritis, which can be acute or chronic. Acute enteritis is usually caused by pathogenic microflora and, with full treatment, ends with complete recovery within a few days. With long-term chronic enteritis with frequent exacerbations, patients also develop extraintestinal symptoms of the disease due to impaired absorption function of the small intestine. They complain of weight loss and general weakness, and they often develop anemia. A deficiency of B vitamins and folic acid leads to cracks in the corners of the mouth (jams), stomatitis, and glossitis. Insufficient intake of vitamin A in the body causes dry corneas and impaired twilight vision. Impaired calcium absorption can cause the development of osteoporosis and the resulting pathological fractures.
Small bowel rupture
Among all the organs of the abdominal cavity, the small intestine is most susceptible to traumatic injury. This is due to the insecurity and significant length of this section of the intestine. An isolated rupture of the small intestine is observed in no more than 20% of cases, and more often it is combined with other traumatic injuries of the abdominal organs.
The most common mechanism of traumatic injury to the small intestine is a direct and fairly strong blow to the abdomen, leading to compression of the intestinal loops against the pelvic bones or spine and damage to their walls.
When the small intestine ruptures, more than half of the victims experience shock and significant internal bleeding.
The only treatment for small bowel rupture is emergency surgery. During surgery, bleeding is stopped (hemostasis), the source of intestinal contents entering the abdominal cavity is eliminated, normal intestinal patency is restored and the abdominal cavity is thoroughly sanitized.
The sooner the operation is performed from the moment of injury to the small intestine, the greater the chance of recovery for the victim.
It is followed by the lean one, and only then by the ileum. The intestine is covered on all sides by a membrane, which is called the peritoneum and is attached to the posterior wall of the abdomen using the mesentery. The human jejunum is located in the left half of the abdominal cavity. It is projected onto the anterior abdominal wall in the umbilical region, on the sides of the abdomen, and also in the left iliac fossa. The intestinal loops are located in horizontal and oblique directions. The length of the jejunum is 2/5 of the total length of the small intestine. Compared to the ileum, the jejunum has thicker walls and a larger diameter of the internal lumen. It also differs in the number of villi and folds that are located in the lumen, the number of vessels, of which there are more, but, on the contrary, there are fewer lymphoid elements. There are no clear boundaries for the transition of one part of the intestine to another.
Wall structure
On the outside, the intestine is covered with a special membrane along its entire length. This is the peritoneum, which protects it and smoothes out the friction of the intestinal loops against each other. The peritoneum converges at the back of the intestine to form the mesentery of the jejunum. It is in it that vessels and nerves pass, as well as those that feed the intestine and carry away from it not only the nutrients needed by the body, but also toxic breakdown products, which are then neutralized by the liver.
The second layer makes up which, in turn, forms two layers of fibers. There are longitudinal fibers on the outside and circular fibers on the inside. Due to their contraction and relaxation, chyme (food that has been exposed to the active substances of the digestive tract in previous sections) passes through the intestinal lumen and delivers all the beneficial substances to the body. The process of sequential contraction and relaxation of fibers is called peristalsis.
Functionally important layer
The previous two layers provide normal function and protection, but the entire process of food absorption occurs in the last two. Under the muscular layer there is a submucosal layer, it is in it that the jejunum has blood lymphatic capillaries and accumulations of lymphatic tissue. The mucous layer protrudes into the lumen in the form of folds, due to which the absorption surface becomes larger. Additionally, the surface of the mucous membrane is enlarged by villi; they can only be seen under a microscope, but their role here is very important. They provide a constant supply of nutrients to the body.
Villi
Villi are processes of the mucous membrane, the diameter of which is only one millimeter. They are covered by cylindrical epithelium, and in the center there are lymphatic and blood capillaries. Also, the glands that are located in the mucosa secrete many active substances, mucus, hormones, enzymes, which contribute to the process of digesting food. The capillary network simply penetrates the mucosa and passes into venules, merging, they, together with other vessels, form which carries blood to the liver.
Function performed by the jejunum
The main function of the intestine is the processing and absorption of food that has been previously processed by previous sections of the digestive tract. The food here consists of amino acids, which were once proteins, monosaccharides, which were once carbohydrates, as well as fatty acids and glycerol (what lipids have become). The structure of the jejunum provides for the presence of villi, it is thanks to them that all this enters the body and can be used as nutritional material. Amino acids and monosaccharides enter the liver, where they are further transformed and subsequently enter the systemic circulation, fats are absorbed by lymphatic capillaries, and then enter the lymphatic vessels, and from there they disperse throughout the body with the lymph flow. Everything that has not passed the test for usefulness in the jejunum ends up in further sections of the intestine, in which feces are finally formed.
From normal to disease - one step
The jejunum has many functions and, in the absence of malfunctions or diseases, functions normally without causing any special problems. But if a failure occurs, then it is worth contacting a specialist in time. It is difficult to examine the jejunum, like the entire small intestine, and tests are of great importance. First of all, it is worth examining feces, which can tell what kind of malfunction occurred in the intestines. But a banal examination and palpation (palpation) will also not be superfluous.
There can be a lot of options for problems in the jejunum, but the main place is occupied by pathology of a surgical, therapeutic and infectious nature. Treatment depends on this, as well as the choice of a specialist who will help get rid of the disease.
Why should you go to the surgeon?
You should contact this specialist if you have a disease that requires surgery to treat. Oncology takes precedence here; malignant and benign processes can be very diverse, and their names depend on what cells the pathologist finds in their composition. Tumor growth can be either into the lumen of the wall or outward. When growth goes into the lumen, bleeding or obstruction occurs, which requires immediate surgical intervention.
It may also be caused by spasms, blockage of the intestinal lumen, or intussusception (when one part of the intestine penetrates into another). Surgical treatment of this variant of jejunal disease also requires urgent surgical intervention. Obstruction may also occur in other parts of the intestine; then a survey radiography of the abdomen becomes important, which will help to correctly establish the diagnosis.
A common pathology is inflammation of the jejunum, which is called a diverticulum. Normally it is not present, and its presence is a congenital pathology. When it is inflamed, timely diagnosis is required, which includes complaints of pain, increased body temperature, and tension in the abdominal muscles. The final diagnosis is made on the operating table and then confirmed by a pathologist.
Other diseases
The jejunum can bring many problems that the surgeon will have to deal with. Sometimes delay in making the correct diagnosis can lead to the death of the patient. Consider Crohn's disease, which can result in bleeding, abscesses and other complications. Some ailments can lead to dysfunction of the jejunum, and in order to restore them, surgery is also required. For example, adhesions in the abdominal cavity, especially in places where this section of the small intestine is located, may require surgical excision of adhesions. Surgical treatment tactics are also used for helminthic infestations, when the lumen is clogged with a ball of helminths.
Why should you go to a therapist?
The therapist also has some work to do. He, of course, has less work than a surgeon, but it is no less responsible. All diseases and inflammatory changes occurring in the jejunum fall on the shoulders of this specialist. These are colitis, which can be acute and chronic, irritable bowel syndrome and other pathologies. The use of a scalpel for these diseases is not required, but competently and correctly prescribed treatment will help get rid of the disease and restore the joy of life.
The infection does not sleep
It is no secret that the jejunum contains a huge number of microorganisms in its lumen. Some of them are good and beneficial to the body, but there are also bad ones that constantly try to cause harm. The immune system holds back the onslaught of pathogenic microflora, but sometimes it fails to cope with its main task, and then infectious diseases begin. Often the body may have unwanted neighbors; helminths strive to get into an excellent habitat, which is the jejunum for them.
Many diseases can develop in the lumen of the small intestine, such as dysentery, cholera, typhoid fever, salmonellosis and many others. The symptoms they cause vary, but one thing they have in common is diarrhea. It can have a different color and smell, be with or without impurities, as well as blood or water. The final point in determining the pathogen will be made by bacteriological examination of the excreted material. Then, based on the sensitivity of the pathogen to antibacterial drugs, appropriate treatment is prescribed. It is also possible to identify helminths; to do this, you should have your stool tested, and only an infectious disease specialist can help you get rid of them.
Duodenum ( intestinum duodenum) emerges from the pylorus, is suspended on a short mesentery, between the layers of which the pancreas is located. In all types of pets it is located in the right hypochondrium, only with its distal end the duodenum protrudes into the renal region, where it turns from right to left and passes into the jejunum without visible boundaries. At the beginning of the duodenum (S-shaped bend at the porta hepatis) two ducts open: the hepatic duct and the main pancreatic duct. Which form a mainly noticeable major duodenal nipple – papilla duodeni maior. Often more distal can be observed minor duodenal nipple – papilla duodeni minor where the accessory pancreatic duct opens.
The duodenum is connected to the stomach, liver, kidneys, as well as the cecum and colon through the following ligaments: gastroduodenal – ligamentum gastroduodenale, hepatoduodenal – ligamentum hepatoduodenale, renal-duodenal – ligamentum renoduodenale, blind duodenum – ligamentum caecoduodenale, colon-duodenal – ligamentum duodenocolicum.
Jejunum ( intestinum jejunum) forms a garland of curls – intestinal loops – ansae intestinalis. It originates from the duodenum after its transition to the left half of the abdominal cavity. The final part (the last curl) of the jejunum, without visible boundaries, continues into the ileum.
Ileum ( intestinum ileum) originates from the last turn of the jejunum and is the shortest part of the small intestine. It is so named because in humans it is located at the ilium. The ileum is connected to the cecum ileo-blind ligament - ligamentum ileocaecale. When it flows into the large intestine, it forms sphincter – m. sphincter ilei, underlying it pacifier – papilla ilealis. The ileal nipple has it outlet – ostium ilealis, and nipple frenulum – frenulum parillae ilealis.
Blood supply of the small intestine is carried out by the branches of the cranial mesenteric artery ( A. mesenterica cranialis): caudal pancreaticoduodenal artery ( a. pancreaticoduodenalis caudalis), collateral trunk ( truncus collateralis) and arteries of the jejunum ( ahh, jejunales). The branches of the celiac artery also participate in the blood supply to the small intestine, namely the duodenum ( a. celiaca): gastroduodenal artery ( a. gastroduodenalis), which is a branch of the hepatic artery arising from the celiac artery ( a. hepatica); as well as the right gastric artery ( A. gasnrica dextra). The nature of branching of intramural arteries in ruminants and carnivores differs among species
Outflow of blood from the small intestine into the tributaries of the portal vein of the same name as the arteries ( v. porta).
Innervated small intestine from the vagus nerve ( n. vagus) and sympathetic trunk ( truncus sympathicus). The branches of the vagus nerve enhance peristalsis of the small intestine and the secretion of intestinal glands. Sympathetic nerves follow the arteries of the small intestine. They reduce peristalsis and secretion, constrict blood vessels, and transmit pain impulses.
Types of features of the small intestine:
In dogs the length of the intestine is 7 times the length of the body. The duodenum is fixed on a long mesentery. It is quite thick, the diameter of the lumen is almost not inferior to that in the large intestine, from the pylorus the intestine is directed obliquely upward and backward in the right hypochondrium, runs along the liver to the right, oriented backwards, rises dorsally and, following under the lumbar muscles, reaches the posterior end of the right kidney . Then, at the level of the 5-6th lumbar vertebrae, it turns to the left and passes forward, and then goes medial to the left kidney between the cecum and colon to the pylorus. Here it descends ventrally and passes into the jejunum. The duodenum has long villi. Peyer's patches and lymphatic follicles are well defined. The bile duct and pancreatic duct enter the duodenum separately, but on one common papilla at a distance of 3-8 cm from the pylorus.
The jejunum is located on the lower abdominal wall and lies on the greater omentum. The intestine hangs on a long mesentery and forms 6-8 loops, and then passes into the ileum without a sharp border. The length of the jejunum is from 2 to 7 meters. There are up to 25 aggregate lymph nodes up to 85 mm long and up to 15 mm wide.
The ileum is directed from the bottom up to the 1st-2nd lumbar vertebrae and opens with a nipple with an outlet at the border of the cecum and colon. Solitary follicles are very small. Peyer's patches of the ileum are short - from 7 to 8.5 mm.
In pigs the small intestine forms numerous skeins. In length (20 m), this section of the intestine occupies an intermediate position between the intestines of carnivorous animals, which eat meat and therefore have a short intestine, and the intestines of herbivores, which, on the contrary, have a very long intestine. The length of the intestine is 18-20 times the length of the body.
The duodenum (40-90 cm) hangs on a short mesentery, it originates from the pylorus of the stomach in the right hypochondrium, passes through the liver and the right leg of the diaphragm caudally to the posterior end of the right kidney. Behind the right kidney, it turns left and returns to the right hypochondrium. Here it continues into the jejunum. The bile duct opens not together with the pancreatic duct, but separately in different places of the intestine (the bile duct is at a distance of 2-5 cm, and the pancreatic duct is 15-25 cm from the pylorus).
The jejunum, up to 20 meters long, forms many loops, is suspended on a long mesentery, and is located between the liver and the conus of the colon. The intestine has up to 38 aggregate lymph nodes, ribbon-shaped, ranging from 50 cm to 3 meters in length.
The ileum follows upward and to the right to the cecum, it opens into the large intestine, at the border between the colon and cecum. At the entrance to the large intestine there is a sleeve-shaped valve.
In cattle the small intestine is long (about 60 meters). Intestinal length; 20-25 times body length. The surface of the mucous membrane has solitary follicles slightly protruding from it, the size of a pinhead in adult cattle. The duodenal glands are located in cattle along 6-9 meters of the length of the intestine, starting from the pyloric sphincter of the abomasum.
The duodenum has a length of 90 to 120 cm and a diameter of up to 7 cm. It follows from the pylorus of the abomasum at the level of the lower ends of the 9-11th ribs, forward and upward to the liver. In the right hypochondrium at the gate of the liver, this intestine forms s-shaped. Bend – flexura sigmoidea. Then it rises obliquely upward and caudally receives hepatic duct – ductus choledochus and duct pancreas – ductus pancreaticus, and approaches the right kidney. Here she turns back. Forming first turn – flexyra prima, and then goes horizontally towards the pelvis, turns to the left at the ilium, where it forms a second turn - Flexyra secunda, and then turns cranially. Forming the third turn - flexyra tertia- and, orienting horizontally forward, again approaches the liver. Here she commits duodenojejunal turn – flexura duodenojejunalis and without a visible border passes into the jejunum. The bile duct flows into the duodenum at a distance of 50-70 cm from the pylorus. The pancreatic duct is separate from the bile duct and is located 30-40 cm distal to it.
The jejunum of cattle lies in the right hypochondrium, in the ileum and inguinal regions. It is very long (up to 40 m), with a diameter of up to 6 cm, bypasses and overlaps the labyrinth of the colon. A garland of loops of the jejunum is suspended on the root of the mesentery so that between the leaves of the mesentery at its root there is the entire spiral disk of the colon, from which the mesentery continues with a kind of fringe onto the loops of the jejunum. Loops of the jejunum lie around the colon. The garland originates from the end of the duodenum in the region of the last rib, approaches the liver and pancreas, and reaches the entrance to the pelvis from behind. The small intestine is located entirely in the right half of the abdominal cavity. The jejunum has ribbon-shaped aggregate lymph nodes ranging from 1 to 52 cm in length. In young animals they reach a length of up to 3 meters. The mucous membrane forms non-expanding transverse folds.
The ileum of cattle originates from the last turn of the jejunum, is located in the right ileum, located between the cecum and the terminal gyrus of the colon. The ileum enters the large intestine right at the border between the cecum and colon, entering from behind and from the right - forward and to the left. Ileal outlet – ostium ileocaecocolicum, located at the level of the fourth lumbar vertebra. There is a damper in the wall of the outlet hole, or circular ileal valve – valvule ileocaecocolica, in the form of a ring-shaped fold of the mucous membrane.
In horses the duodenum is up to one meter long. Its initial part is adjacent to the liver and forms an s-shaped bend on it. The intestine lies predominantly in the right hypochondrium. Along the right lobe of the liver, it rises dorsally and under the right kidney turns caudally (first turn). In the region of the third lumbar vertebra: caudal to the kidney, it turns left and forward the second turn and passes between the roots of the mesentery from the right side to the left and passes into the jejunum without visible boundaries. At the mouth of the bile duct and the confluence of the pancreatic duct, the mucous membrane forms the nipple, separated by a septum from the cavity, or duodenal diverticulum –diverticulum duodeni, into the spherical cavity of which these two ducts open. The duodenal nipple is located at a distance of 10-12 cm from the pylorus. Through the hole, the diverticulum cavity communicates with the intestinal lumen.
The jejunum hangs on a long mesentery (up to 50 cm). The intestine is located in a cup-shaped depression formed by the large colon and cecum. It fills the upper and middle thirds of the left half of the abdominal cavity and is located in front of the cecum. The intestine is up to 30 meters long and up to 7 cm in diameter. There are up to 263 aggregate lymph nodes; they are irregularly oval in shape, up to 6 cm long, up to 14 mm wide.
The ileum is located in the right ileum, where it enters at the level of 3-4 lumbar vertebrae, rising almost vertically upward. Its outlet lies in the concave curvature of the head of the cecum near the outlet of the colon, that is, the ileum flows into the head of the cecum, and does not serve as a boundary between the cecum and colon, as in other animals,
And the ileum. The name comes from the fact that anatomists, when dissecting a corpse, found it empty.
The jejunum is located in the upper left part of the abdominal cavity and is covered on all sides by peritoneum. The jejunum, unlike the duodenum, has a well-defined mesentery and, together with the ileum, is considered the mesenteric part of the small intestine. It is separated from the duodenum by the duodenojejunal L-shaped ligament of Treitz.
There is no pronounced anatomical structure separating the jejunum and ileum. At the same time, the ileum has a larger diameter, its wall is thicker, and it is richer in blood vessels. in relation to the midline, the loops of the jejunum lie mainly on the left, the loops of the ileum on the right. The mesenteric part of the small intestine is covered in front for a greater or lesser extent by the omentum.
The wall of the jejunum has two layers of smooth muscle tissue: the outer longitudinal and the inner circular. In addition, smooth muscle cells are present in the intestinal mucosa.
The length of the jejunum of an adult is about 0.9–1.8 m. It is longer in men than in women. In a living person, the intestine is in a tonically tense state. After death, it stretches and its length can reach 2.4 m. The acidity in the ileum is neutral or slightly alkaline and is in the range of 7–8 pH. The acidity in the jejunum is neutral or slightly alkaline and is normally in the range of 7–8 pH. The motility of the jejunum is represented by various types of contractions, including peristaltic and rhythmic segmentation. The frequencies of this kind of contraction are specific to the jejunum and are normally in the range of 0.131–0.180 Hz.
Some diseases of the jejunum
Some diseases of the jejunum and syndromes (see):
 |
| Jejunal cancer |
- diarrhea (diarrhea), including diarrhea (diarrhea) in children
Angioarchitecture of the jejunum
According to recent studies, the angioarchetictonics (branching order of blood vessels within an organ) of the jejunum can be divided into 4 types (Yang Qin):
Stem(A). The vessels coming from the superior mesenteric artery are immediately divided into two trunks, each of which feeds its own segment. Most often, there is a gap between the feeding trunks, or there are small anastomoses between adjacent arteries in the distal sections. Arc-shaped(b). The main vessel is divided into two trunks that anastomose with each other, forming arcs of the first and sometimes second order. The arcuate variant also has good anastomoses with the branches of adjacent radial vessels, which ensures uniform blood flow in the small intestine.
Branched(V). Pronounced highways maintain a radial orientation similar to a tree trunk, sequentially giving off three or more branches. With this option, the length of the intestinal tube significantly prevails over the length of the mesentery.
Loose or looped(G). The main artery has a short trunk with early and complete division into three or more branches, which then frequently and randomly anastomose with each other, forming several levels of thin arches. The feeding leg of the intestinal segment includes two branches of the first order. The venous network has a loose structure and does not replicate the arterial one.
Knowledge of the angioarchitecture of the jejunum is of great practical importance in reconstructive surgery of the digestive tract after gastrectomy. The stem and arcuate options are considered the most favorable for performing jejunogastroplasty. The loose version is associated with risks of arterial ischemia and venous thrombosis of the intestinal insert.
The jejunum and ileum are combined under the general name intestinum tenue mesenterial, 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 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), however, the typical parts of both sections (the upper part of the jejunum and the 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 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 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.
Absorption of 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 tiny villi, 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 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. Contraction of muscle fibers determines 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.
