Research Area

Digestive System Development


Digestive system development overview

The digestive system consists of two parts: the digestive tract and the digestive gland. The digestive tract is a long, muscular duct from the mouth that continues the pharynx, esophagus, stomach, small intestine, large intestine, and anus. The organs that pass through include the mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum) and the large intestine (cecum, colon, rectum). The digestive gland has two small digestive glands and one large digestive gland. The small digestive glands are scattered in the wall of each part of the digestive tract. The large digestive glands have three pairs of salivary glands (the parotid gland, submandibular gland, sublingual gland), liver and pancreas, all of which are discharged into the digestive tract by means of a catheter. The basic physiological functions of the digestive system are ingestion, transport, digestion of food and absorption of nutrients, and excretion of waste. These physiological processes are beneficial to the coordinated physiological activities of the entire gastrointestinal tract. The digestion and absorption of food, the substances, and energy required by the body, the nutrients in the food, except vitamins, water, and inorganic salts, can be directly absorbed and utilized, and proteins, fats, and sugars cannot be directly absorbed and utilized by the body. It needs to be decomposed into small molecular substances with a simple structure in the digestive tract to be absorbed and utilized. The process by which food is broken down into small molecules that are simple in structure and can be absorbed in the digestive tract is called digestion. The process by which small molecules pass through the gastrointestinal mucosal epithelial cells into the blood and lymph is absorbed. For the portion of the residue that is not absorbed, the digestive tract is excreted in the form of feces through the large intestine.

Digestive system development research status

Evolution of the gut: Most organs of the digestive system are differentiated from the gut. In the third week of the human embryo, the periphery of the third germ layer blastoderm is folded to the ventral side, and the embryo body is changed from disc to column. The endoderm and the visceral mesoderm are wrapped in the embryo body to form a longitudinal tube. The middle ventral side of the original intestine is connected to the yolk sac, which is called the midgut. The head and tail parts of the original intestine are called the foregut and the hindgut respectively. The head of the foregut is swollen into the original pharynx, and the opposite of the mouth is closed by the oropharynx. The tail end of the hindgut is inflated and called the cloaca, and its ventral side is closed with a cloaca membrane at the opposite side of the anal cavity. The oropharynx and cloaca membranes ruptured and disappeared in the fourth and eighth weeks, respectively, causing the ends of the gut to communicate with the outside. As the embryo body and the original intestine grow, the yolk sac is relatively narrowed, and the connection between the yolk sac and the midgut is gradually tapered to form a yolk sac or a yolk tube. As the embryo develops, the endoderm of the gut is differentiated into the epithelial component of most digestive glands. The foregut differentiates the submandibular gland, the sublingual gland, the pharynx, the esophagus, the stomach, the upper end of the duodenum, the liver, the biliary tract, the pancreas, the primordium of the respiratory system, and the thymus, thyroid, and parathyroid glands. The midgut differentiates into the right 2/3 of the digestive tract from the middle of the duodenum to the transverse colon. The hindgut differentiates into an organ that secretes the urinary system from the left 1/3 of the transverse colon to the upper end of the anal canal. The origin of the digestive tract from the esophagus to the rectum is the same as that of the primary endoderm to form its epithelium, and the mesoderm differentiates to form connective tissue and muscle tissue. Therefore, the normal adult body of the digestive tract wall also has a four-layer structure of mucosa, submucosa, muscle layer and adventitia. During the development of the digestive tract, the epithelial cells of the wall become hyperproliferative for a certain period, causing the dysplasia or stenosis of a part of the digestive tract, and the hyperproliferative cells are programmed to die, the epithelium is thinned, and the tube is temporarily narrowed or blocked. The cavity then returns to normal. The evolution of the pharynx: the original pharynx is an enlarged part of the head of the anterior intestine. It is a funnel with a wide left and right width, a flat abdomen, a thick head, and a thin end. There are 5 pairs of sacs on the side wall, called the pharyngeal sac. With the occurrence of embryos, each pair of pharyngeal sacs also undergoes major differentiation and evolution. The occurrence of the stomach: At the 4th week of the embryo, the tail of the foregut is slightly convex before and after, and the left and right slightly flat spindles are swollen, that is, the primordium of the stomach. At first, the stomach primordia are close to the original transverse diaphragm, and its dorsal mesenteric is short and the ventral membrane is long. Then, as the pharynx and esophagus elongate, the stomach also moves to the caudal side, and the dorsal lateral margin grows rapidly, forming a large curvature of the stomach; the ventral margin grows slowly, forming a small curvature of the stomach. The head of the largely curved stomach bulges to form the fundus. As the dorsal mesenteric membrane develops into the omental sac that protrudes to the left side, the large curvature of the stomach turns from the dorsal side to the left side, and the small curvature of the stomach turns from the ventral side to the right side, causing the stomach to rotate 90° to the right. Due to the fixation of the duodenum, the tail end of the stomach is fixed to the posterior wall of the abdomen, and as the liver enlarges, the end of the stomach is pushed to the left, causing the stomach to change from the original vertical position to the upper left. Intestinal development: midgut sputum: At the 4th week of the embryo, the intestine is a straight tube parallel to the longitudinal axis of the embryo. With the appearance of the stomach primordia, it is fixed by fusion with the posterior wall of the abdomen, and the other part of the dorsal membrane grows with the growth of the intestine, and the peritoneum of the intestine all disappears. Since the growth rate of the intestine is much faster than that of the embryo body, the intestines form a "U"-shaped curvature that protrudes toward the ventral side, which is called the midgut. The top of the intestinal fistula relates to the yolk pedicle. The head side of the intestinal fistula connected with the yolk tube is the head branch of the intestinal fistula, and the caudal side segment is the intestinal branch. Transposition of the midgut: In the 6th week of the embryo, the intestinal fistula grows rapidly, the liver and the middle kidney enlarge, and the volume of the abdominal cavity becomes relatively small, causing the intestinal fistula to enter the extraembryonic cavity of the umbilical cord, that is, the umbilical cavity, forming the physiological period of the embryo. While the intestinal fistula continues to grow in the intestinal lumen, the superior mesenteric artery is rotated 90° counterclockwise, causing the intestinal fistula to turn from the sagittal direction to the horizontal orientation, that is, the head branch is turned from the head side of the embryo to the right side. The tail branch turns from the tail side to the left side. A saclike protrusion appears in the tail branch, which is the cecum primordial. At the 10th week of the embryo, due to the enlargement of the abdominal cavity and the atrophy of the kidney, the liver growth slowed down, and the intestinal fistula began to retreat from the umbilical cavity to the abdominal cavity, and the umbilical cavity was closed. When the intestinal fistula is returned to the abdominal cavity, the head branch is first, the tail branch is behind, and the counterclockwise direction is rotated by 180° to make the head branch to the left side and the tail branch to the right side. The intestinal fistula lays the foundation for establishing normal anatomical orientation and adjacent relationship by growth, directional rotation and sequential retraction of the abdominal cavity. In the early stage of retraction of the intestines, the jejunum and ileum are in the middle of the abdomen; the cecum is located higher, below the liver; the anterior segment of the colon traverses the ventral side of the duodenum, and the posterior segment is pushed to the left to become the descending colon. After that, the cecum descends from the bottom of the liver to the right axilla, and the ascending colon forms, and the distal part of the cecum basal is atrophied and degenerates, forming an appendix. The tail of the descending colon moves toward the midline to form the sigmoid colon. Rectal development: The rectum is divided by the cloaca. The cloaca is the bulk of the posterior intestine. The rectum and anal canal are divided and differentiated by the cloaca. The ventral side of the cloaca relates to the Allante, and the tail is closed by the cloaca. From the 6th to 7th week of the embryo, the mesenchyme between the beginning and the intestine of the allantois, forming a sickle-like aponeurosis into the cloaca, called the urinary rectal fistula, which grows rapidly, reaches the cloaca, divides it for the dorsal and abdomen, the central part is called the urogenital sinus, mainly differentiated into the bladder and urethra; the dorsal part is the original rectum, which differentiates into the upper part of the rectum and anal canal. The outer circumference of the anal membrane is a shallow concave, called the anal or the original anal, and the anal recess continues to deepen and evolve into the lower part of the anal canal. The epithelium of the upper segment of the anal canal comes from the ectoderm, and the boundary between the two is called the dentate line. After the anal rupture is absorbed, the tail end of the digestive tract communicates with the outside world.

Digestive system development clinical research

The use of traditional Chinese medicine treatment or psychological counseling is a common method used by treating digestive system diseases and has achieved very satisfactory results. In the treatment of liver and stomach stagnation, Qiu’s use of bupleurum, bergamot, phlegm, and magnolia have the effect of soothing the liver and relieving stagnation, regulating the air-conditioning, and making the patient's liver complex venting. In the treatment of functional constipation, Yip's use of bupleurum, which has the effect of soothing the liver and relieving stagnation, regulates the liver venting, promotes the spleen and stomach. In the treatment of spleen and stomach diseases, Zhu Shi pointed out: "Stomach disease re-adjusts the gas", for the syndrome of liver gas or stomach heat, the use of Chaihu Shugan San or Xiaochaihu decoction and Zuojin Pill addition and subtraction, medicinal Bupleurum, clamshell, Huangqi, Xiangfu, bergamot, turmeric, berberine, Wujing, etc. Shugan Qingre; and attach importance to mental and psychological factors, the treatment effect is obvious. The research on rigid-flexible syndrome theory believes that the onset of psychosomatic diseases often first acts on the liver and develops with the softness of the person. Digestive diseases are mostly psychosomatic diseases and should be treated from the liver. In the treatment of patients with newly diagnosed syndrome, multiple use of white peony, fried jujube kernel, cypress seed, Salvia miltiorrhiza, etc., nourishing liver and softening the liver, promoting blood circulation and collaterals, to inhibit liver excretion too much; in the treatment of patients with flexor syndrome, more use of Sini Xiangfu, turmeric, green skin, dried tangerine peel and other liver, phlegm and collaterals to correct liver effusion. The patient is often psychologically counseled before the drug treatment, and the treatment of psychosomatic treatment has achieved good clinical results in clinical practice. In addition to treatments such as psychotherapy and traditional Chinese medicine, acupuncture treatment, integrated Chinese and Western medicine treatment, and psychological counseling have also achieved good clinical results. Xue et al.used acupuncture to treat diarrhea, liver stagnation, and spleen deficiency syndrome and used acupoints such as Gongsun and Taichong, which have the functions of soothing liver and using a gas-guided method combined with the main point for acupuncture treatment. It is effective and not easy to repeat. Liu in the treatment of stomach pain to soothe the liver and stomach, qi and pain relief as a cure. Selecting the liver's original point, Tai Chong, and the bilateral liver and acupoints to relieve the liver gas, so that the liver gas is reached, and the clinical treatment effect is remarkable. Fuet al. used psychological counseling to treat ulcerative colitis in combination with traditional Chinese medicine and western medicine. It is believed that the treatment of ulcerative colitis can improve the recent cure rate. Shi et al. used psychological counseling combined with traditional Chinese medicine and western medicine to treat children with stomach pain and liver pain, and the clinical symptoms of the children were obviously improved in the short term. In the psychological counseling, the child is instructed to release the unpleasantness of the heart. In the treatment of traditional Chinese medicine, a drug with a liver-releasing stagnation and a stomach-spleen spleen is used, and a gastric mucosal protective agent is used in the treatment of western medicine. After two years, the child's mood was stable, and the disease has not recurred.

Reference

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  2. Gisbert E, Moreira C, Castroruiz D, et al. Histological development of the digestive system of the Amazonian pimelodid catfish Pseudoplatystoma punctifer. Animal. 2014, 8(11):1765-1776.
  3. Solis D R, Rossi M L, Fox E G P, et al. On the morphology of the digestive system of two Monomorium ant species. Journal of Insect Science. 2013, 13(5):70.
  4. Lopez D, Hernández M, Barón B. Ontogeny of the digestive system of Octopus bimaculatus paralarvae. Fish and shellfish larviculture symposium. 2013.
  5. Jiang S, Zhou W, Zhang X, et al. Developmental expression and distribution of nesfatin-1/NUCB2 in the canine digestive system. Acta Histochemica. 2016, 118(2):90-96.

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