消化系統解釋

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, , small intеѕtinе, large intеѕtinе, аnd аnuѕ.

Thеѕе оrgаnѕ соmbinе tо реrfоrm six tаѕkѕ: ingеѕtiоn, ѕесrеtiоn, рrорulѕiоn, digestion, аbѕоrрtiоn, аnd defecation.

  • 攝入;吃東西
  • propulsion; moving the food from the mouth to the intestines for absorption or excretion
  • 消化;食物化學和機械分解成更小的碎片
  • 吸收;可溶性分子的吸收和 
  • Secretion; production of enzymes and other solutions like acid, bicarbonate, etc.
  • defecation; discharge of stool from the body

這些重要功能對於保持健康的體內平衡(維持恆定的內部環境)和人體的最佳功能是必要的。 

Illustration of the digestive system. Servier Medical Art by Servier, CC BY 3.0.

器官及其功能

胃腸道 (GI)

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). 

Teeth in adults and children are involved in the mechanical digestion of food. Servier Medical Art by Servier, CC BY 3.0.

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 是一個強壯的肌肉袋,它會周期性收縮,分解食物並將其與胃分泌物混合;水、鹽酸和蛋白酶(蛋白質消化酶)的混合物。它與胃竇和幽門一起具有較小和較大的曲率。食糜,與胃分泌物混合的半消化食物,通過蠕動(波浪狀運動)推進到腸內,其餘食物被消化和吸收。 

The peristaltic movement of pre-digested food (bolus) through the esophagus. Servier Medical Art by Servier, CC BY 3.0.

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.

Small intestine and villi. Servier Medical Art by Servier, CC BY 3.0.

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.

Microscopic view of the intestinal villi. Servier Medical Art by Servier, CC BY 3.0.

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.

Ascending, transverse, and descendant colon. Servier Medical Art by Servier, CC BY 3.0.

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.

肝臟和膽囊

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.

Macroscopic view of the liver and gallbladder from the back (left) and the front (right). Servier Medical Art by Servier, CC BY 3.0.

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 膽管.膽汁將大的脂肪分子乳化成更小的脂肪滴,這些脂肪滴可以被脂肪酶(脂肪消化酶)有效消化。 

Microscopic view of the liver and gallbladder with the bile ducts and bile canaliculi that collect the bile produced by the hepatocytes. Servier Medical Art by Servier, CC BY 3.0.

外分泌胰腺

胰腺是一個葉狀器官,根據其功能分為兩部分:外分泌胰腺和內分泌(產生激素)胰腺。外分泌胰腺負責產生食物分解所需的所有初級消化酶。胰腺分泌物是以下物質的混合物:

  1. 糖酶 
  2. 蛋白酶 
  3. 脂肪酶 
  4. 碳酸氫鹽和 
Macroscopic and microscopic view of the pancreas. Servier Medical Art by Servier, CC BY 3.0.

唾液腺

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 下頜骨 (jaw bone) and the sublingual glands below the tongue. 

Position of the parotid, sublingual, and submaxillary glands in the head. Servier Medical Art by Servier, CC BY 3.0.

神經和血管供應

神經血管供應是指血液供應和神經供應,這些連接對於保持器官的活力至關重要。消化是由一組不同的神經和血管提供的。 

神經供應

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. 

 肛管下部,梳狀線以下,來源於軀體(隨意)神經,即陰部神經。這使我們能夠控制排便。  

血管供應

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. 

肝臟特別重要,因為它通過肝門靜脈與胃腸道相連,肝門靜脈向肝臟提供營養豐富的血液。肝實質(組織)由起源於腹腔動脈的肝動脈供應,並由肝靜脈引流:下動脈的支流 腔靜脈

了解更多關於消化器官的 3D 空間關係的精彩內容 真人大小的解剖模型。

參考
  1. 解剖學,頭頸,嘴唇,Meghan A. Piccinin;帕特里克·M·齊托。
    https://www.ncbi.nlm.nih.gov/books/NBK507900/
  2. 胃腸道的神經支配:衰老的模式;羅伯特 J. 菲利普斯和特里 L. Powley
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2045700/
  3. 德雷克,理查德 L.;沃格爾,韋恩;米切爾,亞當 WM(2005 年)。 格雷的學生解剖學.賓夕法尼亞州費城:愛思唯爾。第 989-995 頁。 
  4. Snell 的臨床解剖學按區域 10th 版;勞倫斯·E·溫斯基。第 279-500 頁,第 609-700 頁。
  5. Anne MR Agur、Arthur F Dalley 和 Keith L. Moore 的臨床解剖學。頭頸部、腹部、骨盆、會陰部。
  6. 教我解剖學;腹部和骨盆
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173558/#:~:text=The%20principal%20functions%20of%20the,or%20incapable%20of%20being%20digested.
  8. 您的消化系統及其工作原理; https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
  9. 消化系統的四大主要功能; http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm

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