Intestinal dysfunction can be triggered by impaired anatomical organization, digestion and absorption, and barrier function, so the management can also be summarized as nutritional and metabolic therapy, maintenance of intestinal barrier function and reconstruction of the anatomical function of the digestive tract. Clinical nutritional support has been hailed as one of the major advances in medicine in the last quarter of the 20th century. When intestinal dysfunction occurs, there is a significant reduction or complete loss of digestive and absorptive functions, resulting in nutritional deficiencies in the body. Undoubtedly, nutritional support for intestinal dysfunction is an indispensable therapeutic measure.Before the 1970s, when the intestinal digestion and absorption area is insufficient, there is a lack of effective nutritional supplementation methods, and it is difficult for those whose small intestine is shorter than 50cm to survive.In 1968, the use of vena cava tubing for infusion of nutritional solution was advocated by Dudrick and Wilmore.In 1970, the space diet (elemental diet) was applied to the clinic. In 1970, the space diet (elemental diet) was applied to the clinic, which changed the situation that patients could not be supplied with nutrition due to gastrointestinal dysfunction, led to the research of metabolic changes in patients, improved the nutritional status of critically ill patients, increased the cure rate of critically ill patients, and promoted the recovery of patients.After the 1970s, the total venous nutrition was successfully applied to the clinic, which improved the prognosis of patients with short bowel syndrome. At that time, total intravenous nutrition was called “artificial gut”. Now, there is a more comprehensive understanding of intestinal function, the term “artificial gut” is considered to be overrated, and is no longer used. However, parenteral nutrition is still an effective measure for patients with a reduced area of intestinal mucosal absorption and digestion, maintaining nutrition and prolonging life in those patients. It is because of its effectiveness that the Seventh International Conference on Small Bowel Transplantation made the recommendation that parenteral nutrition be preferred in patients with intestinal failure. In order to facilitate the long-term application of parenteral nutrition in patients with intestinal malabsorption such as short bowel syndrome, home nutritional support was proposed. Unfortunately, certain metabolic complications, such as hepatic impairment and osteoporosis, can occur in patients with long-term parenteral nutrition. After half a century of clinical application, it has been confirmed that parenteral nutrition (PN) support can provide the required nutrients that patients can rely on to maintain life when their gastrointestinal tract is non-functional or impaired, such as patients with ultra-short intestines (<30cm). It has been proved that enteral nutrition (EN) support can improve the circulation of the portal venous system, which is conducive to the restoration of intestinal peristalsis, maintenance of the intestinal barrier function, improvement of hepatobiliary function, promotion of protein synthesis, rehabilitation of intestinal loop tissues, modulation of immune function, especially the maintenance of the intestinal barrier function, which makes up for the shortcomings of PN support. EN helps to maintain the structural and functional integrity of intestinal mucosal cells, supports the intestinal mucosal barrier, and can significantly reduce the occurrence of intestinal-derived infections, and its mechanism of action includes: ① Maintaining the normal structure of intestinal mucosal cells, intercellular junctions, and the height of the villi, and maintaining the mechanical barrier of the mucosa; ② Maintaining the normal growth of the intestinal intestinal flora, and maintaining the biological barrier of the mucosa; ③ Contributing to the normal secretion of IgA by the cells in the intestine, and Maintain the immune barrier of the mucosa; ④ Stimulate the secretion of gastric acid and pepsin to maintain the chemical barrier of the mucosa; ⑤ Stimulate the secretion of digestive juices and gastrointestinal hormones to promote the contraction of the gallbladder, gastrointestinal peristalsis, and increase the blood flow of the viscera, so that the metabolism is more in line with the physiological process, which reduces the incidence of hepatic and biliary complications. Especially when the condition is critical, the body's immune function decreases, the intestinal low blood flow state leads to nutritional damage of intestinal mucosa, and at the same time the metabolism is impaired in critical condition, TPN is easy to make the metabolism deviate from the physiological process, and the metabolic complications increase. At this time, EN is particularly important. In the last 40 years, the choice of nutritional support routes can be divided into approximately four phases, changing every 10 years: in the 1970s, "when a patient needs nutritional support, intravenous nutrition is preferred"; in the 1980s, "when a patient needs nutritional support, peripheral intravenous nutrition is preferred "; 1990s, "use the intestine when it is functional and can be used safely"; and currently, "apply total nutritional support, preferring enteral nutrition, and combining enteral and parenteral nutrition when necessary." PN and EN have their own advantages and disadvantages, and in clinical application, they are often used together to complement each other. The most important factor that damages the intestinal mucosal barrier is the insufficient blood and oxygen supply to the intestinal mucosa. This leads to atrophy and apoptosis of intestinal mucosal cells, relaxation of intercellular tightness, and increased permeability, which provides a channel for intestinal bacteria and endotoxin, while the immune barrier is also damaged. Therefore, in order to maintain the intestinal mucosal barrier function, the first step is to regulate the circulation and oxygen supply of the whole organism. When the body is in a state of stress, the blood supply to the intestines is physiologically reduced, and the oxygen supply is also limited. When the body recovers, the recovery of intestinal blood circulation often lags behind the recovery of systemic circulation. The longer the intestinal mucosal blood supply is insufficient, the more damage to the intestinal mucosal barrier function is aggravated. Therefore, attention should be paid to promoting the recovery of intestinal mucosal function after resuscitation. The growth of intestinal mucosal cells requires direct contact with coeliac. This is an important basis for early administration of enteral nutrition. What are the criteria for "early"? Theoretically, the administration of chow should begin as soon as the event occurs. This is possible in animal experiments. Enteral nutrition can be started as soon as the model is made, and in the clinic, enteral perfusion has been started as soon as 6 h after surgery. These are preparatory treatments, while the patient's disease and trauma occur in unprepared conditions. There is often a certain time gap between receiving medical treatment. At the same time, the body is in a state of stress, there are often respiratory and circulatory disorders, there are also internal homeostatic disorders, and sometimes intestinal dysfunction has occurred, and it is difficult to succeed in the intention to give enteral nutrition. After years of clinical practice, enteral nutrition for critically ill patients is mostly given after 24~48h of medical treatment, when respiratory and circulatory disorders have been corrected and internal homeostasis has entered a stable state. Glutamine is a tissue specific amino acid, which is required by rapidly growing cells. Intestinal mucosal cells require glutamine as their primary energy source. Therefore, glutamine should be added to the nutrients to promote the growth of IMCs. Glutamine is a non-essential amino acid, which has low solubility, unstable solution and easy to hydrolyze, so it is not contained in commonly used enteral and parenteral nutritional preparations. Experiments have proved that in the rat model of intraperitoneal infection, glutamine can promote the proliferation of intestinal mucosal cells, effectively maintain the permeability of the intestinal mucosa, which is conducive to the maintenance of the intestinal mucosal barrier function. As for the effect of glutamine given by intestinal infusion or glutamine dipeptide given by parenteral route, there is still different understanding. Some believe that intestinal administration is ineffective, while others believe that intravenous administration of glutamine is not necessary when administering enteral nutrition. The results of our animal experiments illustrate that glutamine given from the gut does have an effect on promoting intestinal mucosal cell proliferation. In the diet, both water-soluble and insoluble fibers stimulate and promote mucosal growth and cell proliferation in the small intestine and colon, but different dietary fibers play different roles in the morphological structure of the intestinal tract, gastrointestinal peristalsis, and nutrient absorption. Insoluble fiber (cellulose) can increase fecal volume and promote intestinal peristalsis; while specific water-soluble fiber (such as gum) can delay gastric emptying and slow down the intestinal transport of food time, and thus has an anti-diarrheal effect. Fermentable soluble fiber (non-starch polysaccharides) can be broken down and metabolized by anaerobic bacteria to produce short-chain fatty acids (SCFA).SCFA (acetic acid, propionic acid, butyric acid) are easily absorbed by the colonic mucosa and utilized as energy, and have a nutritive stimulating effect on both the small intestinal and colonic mucosa to promote the proliferation of intestinal mucosal cells, especially the absorption of water and sodium in the colon. In addition to the mucosal barrier, the intestinal barrier has an immune barrier and a biological barrier. The biological barrier consists of the physiologic secretion of the gastrointestinal tract (gastrointestinal fluids, such as mucus), with the protozoa in the intestine. Intestinal mucus can encapsulate bacteria and toxins. The high acidity of gastric juice is an effective physiological bactericide. In addition to their physiologic functions in the human body, intestinal native bacteria have a restraining effect on pathogenic bacteria. Therefore, while maintaining the barrier function of the intestinal mucosa! It is also necessary to focus on maintaining other barrier functions, do not artificially inhibit and reduce the production and amount of gastric juice. Do not abuse antibiotics to disturb the ecological balance of intestinal bacteria. Many of the fungal infections that occur in the late stages of critically ill patients stem from an imbalance in the ecology of the intestinal bacteria and a barrier disorder of the intestinal mucosa. Reconstruction of the gastrointestinal tract has a variety of surgical approaches, and all have achieved satisfactory results. Currently, minimally invasive techniques are more biologically appropriate. As in the case of other organs, intestinal transplantation is a reasonable therapeutic measure when intestinal function is irreversible. The main indications are short bowel syndrome, congenital malformations and combined multi-organ transplantation. The development of small bowel transplantation has been slower than that of other parenchymal organ transplantation. Prior to the 1970s, hope was pinned on PN, thinking that PN support would provide nutrition and thus sustain the patient's life. However, long-term PN brought serious complications such as severe impairment of liver function and osteoporosis, so that the liver also had to be transplanted. Thus, intestinal transplantation was emphasized again, but it was delayed for about 15 years. However, there was a delay of about 15 years until 1988, when there was a case of successful clinical transplantation. However, due to the high number of lymphocytes in the small intestine, the large number of bacteria in the intestinal lumen, and the complexity of intestinal functions, the rejection rate of intestinal transplantation was high, the infection was serious, the functional recovery was poor, and the overall failure rate was high. 1-year survival rate was 70%, 3-year survival rate was 60%, and 5-year survival rate was 45%. In the 20 years from 1985 to 2005, only 1,210 small bowel transplants were registered worldwide. In recent years, advances in intestinal transplantation techniques, particularly improvements in methods of inducing immunosuppression, have led to an increase in success rates. The principle of selecting indications for small bowel transplantation has changed from "nutritional support is preferred in patients with intestinal failure who can tolerate nutritional support, while intestinal transplantation or liver-intestinal combination transplantation is preferred in patients who cannot tolerate nutritional support and whose condition continues to deteriorate", to "small bowel transplantation should be performed as early as possible in patients with irreversible intestinal failure, both in terms of cost and surgical outcome. The cost and outcome of small bowel transplantation is better than small bowel transplantation after liver failure". Bowel dysfunction is a common clinical organ disorder, and the development of nutritional support has helped to solve the problem of nutritional deficiencies, as well as facilitating the maintenance of the barrier function of the intestinal mucosa. However, the understanding and maintenance of intestinal dysfunction has yet to be studied in depth to obtain more effective measures. Meanwhile, more clinical studies are needed on how to assess intestinal function and screen for effective monitoring indicators.