The digestive system аllоwѕ uѕ to break dоwn the food wе еаt tо оbtаin energy аnd nourishment. It is usually divided into thе gаѕtrоintеѕtinаl tract (also called thе GI tract оr digеѕtivе tract), the liver, pancreas, and gallbladder. The GI trасt iѕ a ѕеriеѕ of hоllоw оrgаnѕ jоinеd in a lоng, twisting tubе frоm thе mоuth to thе аnuѕ. Thе hоllоw organs that mаkе uр the GI trасt аrе the mоuth, esophagus, 胃, small intеѕtinе, large intеѕtinе, аnd аnuѕ.
Thеѕе оrgаnѕ соmbinе tо реrfоrm six tаѕkѕ: ingеѕtiоn, ѕесrеtiоn, рrорulѕiоn, digestion, аbѕоrрtiоn, аnd defecation.
- propulsion; moving the food from the mouth to the intestines for absorption or excretion
- Secretion; production of enzymes and other solutions like acid, bicarbonate, etc.
- defecation; discharge of stool from the body
The mouth is the starting point of the GI tract. A significant amount of mechanical digestion (physical breakdown of food into smaller pieces) occurs in the mouth. The mouth also helps lubricate the food with the saliva helping it move along the pharynx and the esophagus. Speaking of which, the esophagus is a muscular tube that connects the mouth with the stomach and provides a passageway for the bolus (a semi-solid ball of food that has been chewed and mixed with the saliva).
Food reaching the stomach is stored and digested, both mechanically and chemically. Chemical digestion refers to a process by which the body breaks down complex insoluble food molecules e.g., starch into smaller soluble molecules i.e., glucose, amino acids, and fatty acids. The 胃 是一个强壮的肌肉袋，它会周期性收缩，分解食物并将其与胃分泌物混合；水、盐酸和蛋白酶（蛋白质消化酶）的混合物。它与胃窦和幽门一起具有较小和较大的曲率。食糜，与胃分泌物混合的半消化食物，通过蠕动（波浪状运动）推进到肠内，其余食物被消化和吸收。
The small intestine starts from the pylorus of the stomach and is divided into three portions; duodenum, jejunum, and ileum. Most of the digestion occurs in the duodenum and initial jejunum. It is a 5-meter-long luminal structure with a specialized epithelium— the brush border.
This epithelium contains numerous villi and microvilli across its surface. Villi and microvilli are small finger-like projections that increase the surface area (area available for absorption) greatly. These microvilli also give the intestine a towel-like appearance. After most of the soluble nutrients i.e., amino acids, glucose, fructose, fatty acids glycerol are absorbed the food is propelled towards the anus in the large intestine.
The large intestine i.e., the colon starts from the ileocecal junction and extends to the rectum. Ascending, transverse, descending, and the sigmoid colon are all part of the large intestine. The primary function of the colon is to absorb water and electrolytes from the remaining undigested food. The colon also has a series of muscular band loops called tinea-coli which contract to produce bulk movements throughout the colon and help push the feces into the rectum.
The Rectum connects the sigmoid colon to the anus. The feces are temporarily stored in the rectum until it is expelled out of the body through the anus by a process called defecation.
The liver plays a vital function in maintaining a healthy body. In most people, it is located in the upper right abdominal region, below the right dome of the diaphragm and the right lung.
Apart from its numerous other functions like detoxification of exogenous toxic substances, storing nutrients, and synthesis of proteins and triglycerides (fats), the liver also produces bile. Bile is temporarily stored in the gallbladder (attached to the liver) and secreted into the small intestine through the 胆管.胆汁将大的脂肪分子乳化成更小的脂肪滴，这些脂肪滴可以被脂肪酶（脂肪消化酶）有效消化。
Saliva is a watery secretion, produced by glandular structures in the buccal cavity, mixed with enzymes e.g., carbohydrases (carbohydrate digesting enzymes) and lipases. It helps to soften the food bolus and partially digests the food, especially starch (carbohydrates) present in the food. There are three bilateral (present on both sides) sets of salivary glands present in our body. The parotid gland, submandibular gland, and sublingual glands. The parotid glands, present below the ears, are the major salivary glands. As their names suggest, the submandibular glands are located under the 下颌骨 (jaw bone) and the sublingual glands below the tongue.
The buccal Cavity and the structures in it are innervated by cranial nerves (CN), nerves originating directly from the brain or brain stem. Most of the innervation is by CN V (5th), the trigeminal nerve, along with CN IX (9th) and CN X (10th). The 10th CN, the Vagus nerve, supplies most of the GI tract. Stimulation through CN X enhances peristalsis and secretion in the entire GI tract. Another key feature to be noted is that the innervation of most of the digestive system is from the autonomic nervous system, i.e., it is not under voluntary control. The liver and pancreas are innervated by the vagal and splanchnic (sympathetic) nerves.
The mouth’s vascular supply involves different branches of the External Carotid Artery (ECA) e.g., the lingual artery to the tongue. The venous drainage of the mouth is through a series of small veins which eventually drain into the internal jugular vein. The esophagus, stomach, and the proximal (upper) part of the duodenum are supplied by branches of the Celiac (branch of abdominal aorta) artery and drained by adjacent veins back into the celiac vein. The distal part of the duodenum, jejunum, ileum and two-thirds of the transverse colon are all supplied by the Superior Mesenteric Artery (branch of abdominal aorta). The last one-third of the transverse colon, the descending and sigmoid colon, and the anal canal up to the pectinate line are supplied by the Inferior Mesenteric Artery (branch of the abdominal aorta). Below the pectinate line, the anal canal is supplied by the Pudendal Artery. The venous drainage of these structures is through the veins of the corresponding arteries. Most of the pancreas is supplied by the branches of the Splenic artery (branch of Celiac Artery) and drained by the splenic vein.
了解更多关于消化器官的 3D 空间关系的精彩内容 真人大小的解剖模型。
- 解剖学，头颈，嘴唇，Meghan A. Piccinin；帕特里克·M·齐托。
- 胃肠道的神经支配：衰老的模式；罗伯特 J. 菲利普斯和特里 L. Powley
- 德雷克，理查德 L.；沃格尔，韦恩；米切尔，亚当 WM（2005 年）。 格雷的学生解剖学.宾夕法尼亚州费城：爱思唯尔。第 989-995 页。
- Snell 的临床解剖学按区域 10th 版;劳伦斯·E·温斯基。第 279-500 页，第 609-700 页。
- Anne MR Agur、Arthur F Dalley 和 Keith L. Moore 的临床解剖学。头颈部、腹部、骨盆、会阴部。
- 您的消化系统及其工作原理； https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
- 消化系统的四大主要功能； http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm
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