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Chapter 20 The Gastrointestinal System 1. Overview of Gastrointestinal System processes 胃腸道系統過程總覽 2. Functional Anatomy of the Gastrointestinal System 胃腸道系統功能性的解剖構造 3. Digestion and Absorption of Nutrients and Water 營養物及水的消化與吸收 4. General Principles of GI Regulation 胃腸道調控的一般性原則 5. GI Secretions and its Regulation 胃腸道的分泌及其調控 6. GI Motility and its Regulation 胃腸道的活動性及其調控 P569 I. Overview of Gastrointestinal System processes P570 Most of the nutrient molecules in food are too large to be transported into the bloodstream 血流 These molecules must be chemical broken down to smaller molecules 化學性分解成較小的分子by enzymes in the lumen of the GI tract 胃腸道 管腔內的酵素 , a process called digestion 消化 Once the larger nutrient molecules have been reduced to smaller digestive end-products 較小的消化產物, these molecules are transported into the bloodstream 運送進入血流 via a processes called absorption 吸收 To aid in digestion and absorption, fluids containing enzymes and other substances are transported into the lumen of the tract 含酵素及其他物質 的液體被運送到胃腸道管腔內 via a process called secretion 分泌 As these processes are occurring, the contents of the lumen are mixed and slowly propelled 管腔內的內容物被混合並往前推動 from one end of the tract to the other by the contractile activity of muscle located in the wall of the tract itself 胃腸道管壁上的肌肉之收縮活性, which gives digestive organs the ability to move 消化道器官有移動的能力, called motility 能動性 口 食道 胃 Figure 20.1 Overview of four basic digestive processes: digestion, absorption, secretion, and motility. 附屬腺體 能動性 分泌 消化 小腸 吸收 心臟 大腸 糞便 直腸及肛門 肝臟 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P571 II. Functional Anatomy of the Gastrointestinal System The gastrointestinal system 胃腸系統 (digestive system 消化 系統) comprises two divisions: — The gastrointestinal tract (GI tract or digestive tract) 胃腸道； 消化道 is several organs jointed in series to form a passageway 許多器官串聯在一起形成通道 through which food and digestion products are conducted The accessory glands 附屬腺體 a number of glands located outside the GI tract 位在消化道外面的腺體 that secrete various fluids and enzymes into the lumen of the tract to aid the digestive process 分泌各種液體及酵素進入消化道管腔，幫助消化 P570 The Gastrointestinal Tract 消化道器官 附屬腺體及相關構造 口 唾液腺 咽 The GI tract is essentially a hollow tube 中空的管子 approximately 4.5 meters long that runs through the body and opens to the outside at either end (mouth 口 & anus 肛門) 氣管 食道 橫膈 肺臟 肝臟 胃 膽囊 胰臟 P570 小腸 結腸 盲腸；闌尾 直腸 肛門 Figure 20.2 Major structures of the gastrointestinal system. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P572 Generalized structure of the gastrointestinal wall The wall of most of the GI tract (exceptions 除外 being the mouth 口, pharynx 咽, upper third of the esophagus 食道, and external-most portion of the anus 肛門) has the same general features there are four distinct layers P570 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 腸細胞 黏膜下層 的腺體 附屬腺體 的管道 血管 Mucosa 黏膜層 – lines lumen Submucosa 黏膜下層– connective tissue Muscularis Externa 外肌層– smooth muscle Serosa 漿膜層 – connective tissue 黏膜 管腔 固有 層 淋巴結節 黏膜層 黏膜肌 層 環狀肌 黏膜下層 外肌層 縱狀 肌 腸系膜 Figure 20.3 Generalized structure of the GI wall, depicting the four major layers and the tissue within them. 漿膜層 黏膜下神經叢 腸肌神經叢 腸神經系統 P573 Mucosa 黏膜層 The mucosa is composed of three layers: Mucous membrane 黏膜—an innermost layer 最內層 of epithelial cells 上皮細胞 (enterocytes 腸細胞) Separates GI lumen from internal environment 分隔消化道管腔與內在環境 Enterocytes are classified as absorptive 吸收 cells, exocrine 外分泌 cells, endocrine 內分泌 cells Goblet cells 杯狀細胞 (exocrine cells) secret mucus 黏液 throughout the length of the GI tract Lamina propria 固有層—a middle layer of connective tissue 結締組織 Contained within this layer are small blood vessels 小血管, nerves 神經, and lymphoid tissue 淋巴組織 Lymph nodules 淋巴結 and Peyer’s patches are important in defending the body against bacteria 對抗細菌感染 Muscularis mucosae 黏膜肌層—an outer layer of smooth muscle 平滑肌 Severs primarily to contract the mucosa into folds 使黏膜層產生皺摺, which stirs the lumenal contents 攪動管腔內容物 and promotes contact with the mucosal surface 增加與粘膜的接觸 P572-573 Submucosa 黏膜下層 Submucosa 黏膜下層—a thick layer of connective tissue that provides the GI tract with much of its distensibility 膨脹性 and elasticity 彈性 enable it to tolerate a large degree of stretch 能耐受拉扯 At its outer border 外圍 is a network of nerve cells 神經細胞網路 known as the submucosal plexus 黏膜下神經叢 (Meissner’s plexus 麥斯納神經叢), which communicates with another nerve cells network in the muscularis externa 外肌層 called the myenteric plexus 腸肌神經叢 (Auerbach’s plexus 歐爾巴克神經叢) together these nerve plexus 神經叢 make up the enteric nervous system (ENS) 腸神經系統 The ENS is an elaborate network of sensory neurons 感覺神經, motor neurons 運動神經, and inter-neurons 中間神經元 located with the wall of the GI tract plays an important role in the control of digestive function Thick layer connective tissue 一層厚的結締組織 distensibility & elasticity Large blood vessels and lymphatic vessels 分佈大的血管及淋巴管 Submucosal plexus (Meissner’s plexus) part of enteric nervous system P573 Muscularis Externa 外肌層 Muscularis externa 外肌層—is largely responsible for the motility of the GI tract 使胃腸道具有能動性 and contains two separate layers of smooth muscle 平滑肌 Inner layer 內層 of circular muscle 環狀肌 consists of single-unit smooth muscle 單一單位平滑肌 capable of generating spontaneous depolarizations 可產生自發性去極化, called slow-wave 慢波 potentials Outer layer 外層 of longitudinal muscle 縱狀肌 consists of multi-unit smooth muscle 多單位平滑肌 that depends on neural input for contraction 依賴神經訊息來收縮 Coordinated 協調 of the circular and longitudinal muscles propels the lumenal contents 推動管腔內容物 through the GI tract and mixes the contents with secretions 混合內容物與分泌物 that help digest food particles Two layers of smooth muscle Inner circular layer (changes diameter 直徑改變) Outer longitudinal layer (changes length 長度改變) Myenteric plexus (Auerbach’s plexus) Second part of enteric nervous system P573-574 Single-unit versus multi-unit smooth muscle 自律神經囊節 Located in large airways 呼吸道 and arteries 動脈 Few if any gap junctions Each fiber acts individually receives own innervation 神經支配 空隙聯合 P354 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Location: gastrointestinal tract 消化道; uterus 子宮 Muscle fibers activated synchronously 協同性 fibers connected by gap junctions contract together as a single unit Serosa 漿膜層 Serosa 漿膜層—the outermost layer 最外層 of the GI tract Inner layer of fibrous connective tissues 纖維結締組織 provides structural support 結構支撐 Outer layer of epithelial tissues called the mesothelium 間皮 secretes a watery lubricating fluid 分泌水性的潤滑液 that makes it easier for organs to slide past one another The mesothelium continuous 連續 with mesenteries 腸繫膜, a system of clear, thin membranes that interconnects most of the abdominal organs and houses nerves and blood vessels running to them 腸繫膜把腹腔大多數的器官及其神經和血管相互結合起來 Inner layer connective tissue Outer layer of epithelial tissue = mesothelium 間皮 Mesothelium continuous with mesenteries which is continuous with peritoneum 腹膜 P574 Functional anatomy of gastrointestinal tract organs 口 咽 會厭 牙齒 舌頭 上食道 括約肌 食道 胃底 Mouth, pharynx, and esophagus 口、咽及食道 Stomach 胃 Small intestine 小腸 Colon 結腸 Rectum and anus 直腸及 肛門 下食道括約肌 幽門括約肌 皺折 幽門 胃竇 胃體 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.4 Anatomy of the mouth, pharynx, esophagus, and stomach. P574 Mouth, Pharynx, and Esophagus 口、咽及食道 In the mouth (oral cavity口腔), food is chewed (mastication 咀嚼) to decrease the size of food particles 減小食物顆粒 and to mix with a secretion called saliva 將食物與唾液混合 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 口 牙齒 咽 會厭 舌頭 Saliva lubricates the food 潤滑食物 and contains an enzyme called saliva amylase 唾液 澱粉酶, which begins the digestion of carbohydrates 碳水化合物 by breaking down starch 澱粉 and glycogen 肝醣 在口腔已經開 始進行碳水化合物的初步消化分解 From the mouth, the food-saliva mixture is propelled by the tongue 舌頭 into the pharynx 咽 (throat 喉嚨), a common passageway for food and air 食物及空氣共通性的通道 上食道括約肌 食道 下食道括約肌 P574-575 The esophagus 食道 is a muscular tube 肌肉性的管子 whose primary function is to conduct food 主要功能為輸送食物 from the pharynx to the stomach 胃 Mouth, Pharynx, and Esophagus 口、咽及食道 The esophagus is unusual 獨特的among the organs of the GI tract in that its wall contains both skeletal muscle 骨骼肌 (in the upper third of its length) and smooth muscle平滑肌 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 口 牙齒 咽 會厭 舌頭 上食道括約肌 —The movement of food from the pharynx to esophagus is regulated by the upper esophageal sphincter 上食道括約肌, a ring of skeletal muscle surrounding the esophagus at its upper end —The lower esophageal sphincter 下食道 括約肌, a ring of smooth muscle that regulates the flow of food from the esophagus to the stomach 食道 下食道括約肌 P574-575 大腦皮質 體運動神經 (somatic motor neuron) skeletal muscle 隨意肌 自律神經 (Autonomic motor neuron) smooth muscle 不隨意肌 Single-unit smooth muscle 慢波電位 (slow wave potential) 自發性收縮 Stomach 胃 An important function of the stomach 胃 is to store food 儲存食物 after it is swallowed and to release it into the small intestine 小腸 P574-575 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 胃底 幽門括約肌 皺折 幽門 胃竇 allow the stomach to expand approximately 20 times 擴張將近 20倍 from its empty volume (50 ml) expands to full volume (1000 ml) 胃體 The stomach has three major anatomical regions: Fundus 胃底—the wall is thin and easily expands 薄且容易擴張 to accommodate increases following a meal 飯後的容量增加 Body 胃體—the gastric mucosa 胃黏膜 is thrown into longitudinal folds 縱狀皺折 called rugae 皺折, which flatten as the stomach expends Antrum 胃竇 —has the thickest muscle layer 厚的肌肉層 and produces strong contractions 產生很強的收縮 responsible for gastric mixing and emptying 負責混合及胃排空 Stomach 胃 The lining 內層of the stomach contains glands (gastric glands 胃腺) that secrete a watery fluid 分泌水性的液體 called gastric juice 胃液 into the lumen 管腔 contractile activity 收縮活性 of stomach mixes food with gastric juice 將食物與胃液混合 forming a mixture called chyme 食糜 胃底 幽門括約肌 皺折 幽門 胃竇 胃體 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Contraction of the antrum propel chyme from the stomach into the small intestine, a process called gastric emptying 胃排空 is regulated by pyloric sphincter 幽門括約肌, a surrounding ring of smooth muscle 胃小凹 黏膜層 Both the fundus and body contain gastric pits 胃小凹, which contain cells that secrete the products found in gastric juice 胃小凹中有細胞可分泌胃液中的成分 胃腺 P574-575 Stomach 胃 Gastric pits 胃小凹 contain a variety of secretory cells, including both exocrine and endocrine cells — Chief cells 主細胞, which secreted pepsinogen 胃蛋白酶原, the precursor for a proteolytic enzyme 蛋白水解酵素 called pepsin胃蛋白酶 P574-575 胃小凹 — Hydrogen ions secreted by parietal cells 壁細胞 maintain acidic environment of stomach necessary for converting pepsinogen to pepsin; Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. denature proteins 蛋白質變性 & kills many foodborne bacteria 殺死食物中的細菌 黏膜層 — Intrinsic factor 內生性因子 secreted by parietal cells necessary for absorption of vitamin B12 頸細胞(分泌黏液) 主細胞 壁細胞 — Gastrin 胃泌素 (endocrine) secreted from G cells — Mucus 黏液 secreted from neck cells 頸細胞 combine with bicarbonate (secrete from surface epithelial cells— goblet cells) form the gastric mucosal barrier 胃黏膜屏障 Small Intestine 小腸 The small intestine, a coiled tube 纏繞的 about 2.5-3 meters long that is the primary site 主要位置 for the digestion 消化 and absorption 吸收 of all nutrients 營養物 The small intestine is divided into three major regions: an initial portion called the duodenum 十二指腸, a middle portion called the jejunum 空腸, and a terminal portion called ileum 迴腸 Figure 20.5 Anatomy of the small intestine. 胃 十二指腸 Bicarbonate neutralizes中和 the acid in the chyme, which is necessary because the enzymes in pancreatic juice function at the normal pH of the small intestine (which is slightly basic 稍微偏鹼性) 空腸 迴腸 小 腸 P577 In the duodenum, chyme is mixed with a watery secretion 水性分泌液 from the pancreas 胰臟 called pancreatic juice 胰液, which contains a wide variety of digestive enzymes 消化性酵素 and is rich in bicarbonate 富含碳酸氫根(鹼性) The duodenum also receives bile 膽汁, a fluid secreted by the liver that contains bicarbonate and bile salts 膽鹽, which aid in the digestion of fats 幫助消化脂肪 Copyright © 2008 Pearson Education, Inc., P575-576 publishing as Benjamin Cummings. Small Intestine 小腸 The simultaneous 同時的 processes of digestion and absorption begin in the duodenum 十二指腸 and continue to completion 完成 in the remainder 其餘的 of the small intestine Absorption is typically completed within the first 20% of the small intestine’s length 在小腸的前20%就幾乎完成所有營養物的吸收 the small intestine has a large excess capacity for absorpting nutrients Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 頂端膜 微絨毛 刷狀邊緣 絨毛 李培昆氏 凹窩 吸收細胞 微血管 The small intestine’s absorptive efficiency is 基底 attributable to the fact that 外側膜 the mucosal surface is highly folded (villi 絨毛) and the presence of a brush border 刷狀邊緣 (make up of microvilli 微絨毛) on the mucosal surface 黏膜表面 乳糜管 小靜脈 小動脈 淋巴管 動脈 靜脈 P575-576 Small Intestine 小腸 Villi 絨毛 increase surface area 增加表面積 by roughly a factor 10 contain blood vessels 血管 and lacteal 乳糜管 for absorption of nutrients Microvilli 微絨毛 increase surface area by factor of 20 form brush border 刷狀邊緣 contains several digestive enzymes located on the tips 頂端 of villi brush border enzymes 刷狀邊緣酵素 Epithelial cells in crypts of Lieberkuhn 李培昆氏凹窩；小腸隱窩 secrete bicarbonate-rich fluid succus entericus 腸液 頂端膜 微絨毛 基底 外側膜 刷狀邊緣 絨毛 李培昆氏 凹窩 吸收細胞 微血管 The succus entericus 腸液 is secreted mostly in the more proximal portions of the small intestine 在小腸前端分泌 and is almost completely absorbed before the chyme reaches the colon 在小腸遠端接近結腸處完全 被吸收 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P576-577 下腔大靜脈 Blood from intestinal capillaries drains into mesenteric veins 腸繫膜 靜脈 and is carried to the liver by the hepatic portal vein 肝門靜脈 (deoxygenated blood 去氧血), which extracts certain nutrients for further processing 萃取營養物做進一步的處理 But a supply of oxygenated blood 含氧血 is delivered to the liver by the hepatic artery 肝動脈 Blood is carried from the liver to the general circulation by the hepatic vein 肝靜脈, which drains into the inferior vena cava 下腔大靜脈 Figure 20.6 Circulatory route of materials absorbed in the small intestine and colon. Materials absorbed in the intestines travel to the liver via the mesenteric veins and the hepatic portal vein, and then into the general circulation via the hepatic vein. 肝靜脈 從主動脈 來的血液 肝臟 肝動脈 肝門靜脈 電解質及水分 營養物、電解質及水分 腸繫膜 靜脈 結腸 小腸 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P577-578 Colon 結腸 The colon 結腸 is divided into four major regions: Ascending colon 升結腸 Transverse colon 橫結腸 are specialized for absorbing water and ions from chyme Descending colon 降結腸 Sigmoid colon 乙狀結腸 Although the wall of the colon has the same fundamental structure as other parts of the GI tract, the longitudinal muscle layer of the muscularis externa is not continuous but is instead compressed into three relatively narrow bands called teniae coli 結腸帶, which run the colon’s length storage depot for whatever material remains in the lumen after absorption has occurred 儲存吸收後仍然剩下的任何物質 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 橫結腸 結腸帶 升結腸 降結腸 盲腸 闌尾 直腸 乙狀結腸 Figure 20.7 Major anatomical features of the colon. P577-578 Colon & Rectum and Anus 直腸及肛門 At the junction between the ileum 迴腸 and colon 結腸, the flow of material is regulated by a ring of smooth muscle called the ileoceal sphincter Together, the cecum 盲腸, colon 結腸, and rectum 直腸 constitute what is often referred to as the large intestine 大腸 The movement of feces 糞 through is controlled by the two sphincters 括約肌: 迴盲括約肌 The internal anal sphincter 內肛門括約肌 is composed of smooth muscle The external anal sphincter 外肛門括約肌 a ring of skeletal muscle 骨骼肌 that controls the opening to the outside Relaxation 鬆弛 of both sphincters, which are normally closed, allows fecal material to be eliminated from the body, a process called defecation 排便 盲腸 闌尾 乙狀結腸 直腸 內肛門括約肌 外肛門括約肌 肛門 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P577-578 Accessory Glands The accessory glands 附屬腺體 of the digestive system include: — The salivary glands 唾液腺, which secrete saliva 唾液 — The pancreas 胰臟, which secretes pancreatic juice 胰液 — The liver 肝臟, which secretes bile 膽汁 Secretions 分泌物 of these glands are carried to the GI tract via ducts 導管 lined branch extensively, terminating in an enclosed space that is completely by a layer of specialized secretory epithelial cells Figure 20.8 Generalized structure of an accessory gland. The gland depicted here is typical of the salivary glands or the pancreas, in which the body of the gland contains acini 腺泡 and associated ducts. Heavy arrows at right indicate the formation of the primary secretion in an acinus. Lighter arrows indicate modification of this secretion by the transport of ions and water within the ducts. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 腺泡 主要分泌物 在運送的過程 改變離子及水量 腺體 主導管 往消化道管腔 上皮細胞 P578-579 Salivary Glands Saliva 唾液 is produced by three pairs of major salivary glands 唾液腺 among the components of saliva are: — Bicarbonate (HCO3-), which makes the saliva alkaline 鹼化 and helps to neutralize acid 中和酸 — Mucus 黏液, which lubricates the food 潤滑食物 and protects the lining of the mouth from abrasion 保護嘴巴內層不會剝落 — Salivary amylase 唾液澱粉酶, a digestive enzyme that breaks down 分解 starch 澱粉 and glycogen 肝醣 舌頭 腮腺 (耳下 唾液腺) 舌下唾液腺 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. — Lysozyme 溶菌酵素, an enzyme that destroying or lysing certain bacteria 破壞或溶解細菌 helps to prevent tooth decay 預防牙齒腐敗 顎下唾液腺 Figure 20.9 Location of the major salivary glands. P578-579 Pancreas The pancreas 胰臟 is not only an exocrine organ 外分泌器官 of the digestive system but also an endocrine organ 內分泌器官 that secretes hormones important in the regulation of metabolism 調控代謝 The exocrine pancreas comprises the numerous acini 腺泡 and their associated ducts 相關的管子 pancreatic juices 胰液 is rich in: — Bicarbonate 重碳酸 neutralized acid 中和酸 — Pancreatic amylase 胰澱粉酶 breaks down starch and glycogen — Pancreatic lipases 胰脂肪酶 breaks down fats — Proteases 蛋白水解酶 breaks down proteins — Nucleases 核酸水解酶 breaks down nucleic acids P579 腺泡細胞 分泌酵素 肝管 外 分 泌 性 的 胰 臟 總肝管 膽囊 島細胞 分泌荷爾蒙 總膽管 管細胞分泌含 重碳酸的液體 胰臟 十二指腸 歐迪氏 括約肌 胰管 壺 腹 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.10 The pancreas and associated structures. P580 Liver The liver 肝臟, the largest organ in the abdominal cavity 腹腔最大的 器官, is amazing 驚人的 versatile 多功能 1. Secrete bile 分泌膽汁 contains bicarbonate, phosphate, inorganic acids, and bile salts 膽鹽, which are derivatives 衍生物 of cholesterol 膽固醇 2. Metabolic processing of nutrients 代謝性處理營養物 absorbed glucose glycogen 將葡萄糖合成肝醣或將肝醣分解成葡萄糖 absorbed amino acids fatty acids ketones 將胺基酸合成脂肪酸或將 脂肪酸分解成酮體 triglycerides and cholesterol synthesis lipoprotein 合成三酸甘油脂及膽 固醇，並進一步合成脂蛋白 gluconeogenesis glucose 進行醣質新生合成葡萄糖 ammonia (from amino acid catabolism) urea 將胺基酸代謝的產物— 氨—代謝合成尿素 P579 Liver 3. Removal of old red blood cells 去除老舊的紅血球 Catabolize hemoglobin iron + bilirubin 分解紅血球中的血紅素，回收 鐵離子並排出膽紅素 4. Elimination of wastes and toxins 排除廢棄物及毒素 Bilirubin eliminated as bile pigments 膽紅素及其他類似的血紅素分解物形 成膽色素，使糞便呈現顏色 Excess cholesterol, foreign 外來物 (drugs 藥物 or poisons 毒物) bile 過量的膽固醇及一些外來物也可從膽汁排除 5. Synthesis of plasma proteins 合成血漿蛋白 Albumin 白蛋白, hormone-binding proteins, clotting proteins 凝血因子, angiotensinogen 血管張力素原... 6. Secretion and modification of hormones 分泌及修飾賀爾蒙 Activation 活化 of vitamin D, secrete 分泌 somatomedin 體介素 (insulin-like growth factor) growth hormone P579-580 Liver Because it manufactures and secretes bile 膽汁, the liver is part of the biliary system 膽道系統 liver, gallbladder 膽囊, associated ducts — Liver synthesizes bile 肝臟合成膽汁 肝管 — Gallbladder stores bile 膽囊儲存膽汁 肝臟 膽囊管 總肝管 總膽管 膽囊 胰管 歐迪氏 括約肌 壺腹 — Common bile duct 總膽管 transports bile 運送膽汁 from liver and/or gallbladder to duodenum 從肝臟或膽囊到十二指腸 — Common bile duct joins with pancreatic duct to form Ampulla of Vater 總膽管與 胰管匯集形成壺腹 — Sphincter of Oddi 歐迪氏括約肌, which is normally closed 平常關閉 but Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. opens when food is present 有食物時 Figure 20.11 Structures of the biliary 打開 regulates flow from pancreas and gallbladder to duodenum system. (a) Gross anatomy of the liver, gallbladder, and their associated ducts. 調控胰液及膽汁至十二指腸的流速 十二指腸 P581 P580 Liver The liver contains numerous blood-filled cavities 充血的空腔 called sinusoids 竇狀隙, which take the place of true capillaries 微血管 The blood that fills these sinusoids in a mixture of oxygenated blood 含氧血 flowing from branches of the hepatic artery 肝動脈, and deoxygenated blood 去氧血 flowing from branches of the portal vein 肝門 靜脈 blood leaves the sinusoids via branches of the hepatic vein 肝靜脈 肝門靜脈分枝 膽管 膽小管 (含膽汁) 肝細胞 肝動脈分枝 竇狀隙 (含血液) 肝靜脈分枝 The walls of the sinusoids consist of sheet-like layers of liver cells 肝細胞 (hepatocytes) the cells take from the blood the raw materials for making bile and then secrete the bile into the bile canaliculi 膽小管 bile ducts 膽管 common hepatic duct 總肝管 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.11 Structures of the biliary system. (b) Microscopic anatomy of the liver, showing hepatocytes, sinusoids, and bile cancliculi. P580-581 P582 III. Digestion and Absorption of Nutrients and Water Most of nutrients (carbohydrates, proteins, lipids) are consumed as macromolecules 大分子 that must be enzymatically broken down 酵素性分解 into smaller molecules 小分子 before they can be absorbed, a process called chemical digestion or simply digestion 消化 Carbohydrates 碳水化合物 Proteins 蛋白質 Lipids 脂質 Vitamins 維他命 Minerals and water 礦物質及水 Digestion absorption Absorption P581 Carbohydrates—digestion Most carbohydrates in the diet are in the form of polysaccharides 多醣類, such as starch 澱粉 and cellulose 纖維素 from plants and glycogen 肝醣 from animals Cellulose cannot be digested, as it is not a substrate 受質 of digestive enzyme it is a major component of dietary fiber 膳食纖維and it aids in intestinal motility 幫助腸道蠕動 Polysaccharides are digested by amylase 澱粉酶 located in saliva and pancreatic juice maltose 麥芽糖 (disaccharides of glucose) or short, branched 短鍊分岔的 polysaccharides (limit dextrins 糊精) 葡萄糖單位體 唾液或胰澱粉酶 cannot break bonds at the end or at branch points 澱粉 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 糊精 麥芽糖 (雙糖) Figure 20.12 Digestion of starch by salivary or pancreatic amylase. Complete digestion of starch by amylases produces maltose and limit dextrins. P581-582 Carbohydrates—digestion Only monosaccharides 單醣 can be absorbed digestion of carbohydrates to monosaccharides is completed by a variety of brush border enzymes 刷狀邊緣酵素 bound to the apical membrane of absorptive cells lining the small intestine Absorption The brush border enzymes 刷狀邊緣酵素 include: — Dextrinase 糊精酶 – limit dextrins glucose — Glucoamylase 葡萄糖澱粉酶 – straight-chain glucose plymer glucose — Sucrase 蔗糖酶 – sucrose fructose + glucose — Lactase 乳糖酶 – lactose galactose + glucose — Maltase 麥芽糖酶 – maltose 2 glucose Absorption Lactose intolerance 乳糖不耐受症 develops when cells begin to stop producing lactase, such that the enzyme concentration falls drinking milk lactose remains in the lumen of small intestine serving as a nutrient for bacteria 細菌 bacteria growth production of gas and other waste bloating 脹氣, discomfort 不適, and diarrhea 腹瀉 P582-583 Carbohydrates—absorption Once carbohydrates have been digested to monosaccharides, they are absorbed by carried-mediated transport across epithelial cells lining intestinal villi 消化後的單醣藉由媒介性運送穿越小腸絨毛內層的上皮細胞 而被吸收 麥芽糖 葡萄糖 管腔 刷 狀 邊 緣 麥芽糖酶 頂端膜 吸收細胞 基底外側膜 間質液 血液 微血管 到肝臟 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.13 Digestion and absorption of maltose. Maltose, a disaccharide consisting of two glucose monomers, an end-products of starch digestion by amylase, is digested by maltase, a brush border enzyme. The endproducts, glucose monomers, are transported across the apical membrane of mucosal epithelial cells by sodium-linked secondary active transport. Energy for this process is derived from the action of Na+/K+ pumps in the basolateral membrane, which create an inwardly directed electrochemical gradient for sodium ions. Glucose molecules exit cells by facilitated diffusion across the basolateral membrane and then diffuse into capillaries, which carry them into the general circulation. Fructose 果糖 facilitated diffusion Glucose & galactose sodium-linked secondary active transport P583-584 Proteins—digestion Proteins 蛋白質 enter the GI tract through ingestion 攝取, secretion 分泌 (mucins 黏蛋白 and enzymes), and the turnover of enterocytes 腸細胞的 新陳代謝, which get sloughed 脫皮 into the lumen of the GI tract Proteins must be digested 消化 to tripeptides 三胜肽, dipeptides 雙胜肽, and amino acids prior to absorption 吸收前 digestion of proteins requires two types of enzymes: Endopeptidases 內胜肽酶—split polypeptides at interior peptide bonds small peptides 將多胜肽從內切開形成小的胜肽片斷 Exopeptidases 外胜肽酶—cleave off amino acids from one end of the polypeptides amino acids 將多胜肽從末端把胺基酸一個一個切開 To protect the epithelial cells from the proteolytic action of these enzyme, the enzymes are stored in epithelial cells in an inactive form, called zymogens 酵素原 secreted by exocytosis 為了保護上皮細胞不受到酵素的蛋白水解作用，這些酵素都以去活化的酵素原 型態儲存在上皮細胞的小泡內，再以胞吐的方式分泌出去 P583 Digestion of proteins to smaller peptides and amino acids—stomach 管 腔 蛋白質 小胜肽 片段 胃蛋白酶 胃蛋白酶原 部分活化的 胃蛋白酶原 胃黏膜 主細胞 壁細胞 Figure 20.14 Activation and activity of pepsin in the stomach. Chief cells 主細胞 secrete pepsinogen胃蛋白酶原, which is partially activated 部分活化 by hydrochloric acid (HCl) secreted by parietal cells 壁細胞. Partially activated pepsinogen molecules (pepsinogen*) then fully activated 完全活化 other pepsinogen molecules by cleaving off 切除 amino acids to form pepsin 胃蛋白酶 (an endopeptidase 內胜肽酶), which digests proteins to small fragments 小片段. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Pepsin 胃蛋白酶 can then start digestion of protein 開始消化蛋白質 in the lumen of the stomach 胃, but it cannot complete digestion 不能完全消化 to individual amino acids because its actions are limited to splitting bonds between certain amino acids only 受限於胃蛋白酶只可切除某些胺基酸間的鍵結 P584 Digestion of proteins to smaller peptides and amino acids—small intestine The pancreas 胰臟 secretes several zymogens into the duodenum 十二指腸, including trypsinogen 胰蛋白酶原, chymotrypsinogen 胰凝乳蛋白酶原, and procaroboxypeptidase 羧基端胜肽酶原 Like pepsin, trypsin and chymotrypsin 胰凝乳蛋白酶 are endopeptidase, which limits their ability to fully digest proteins carboxypeptidase 羧基 端胜肽酶 and a brush border enzyme, aminopeptidase 胺基端胜肽酶, are exopeptidases that finish protein digestion amino acids, dipeptides, and tripeptides Figure 20.15 Activation of proteases in the small intestine. 胰管 小腸管腔 胰蛋白酶原 胰凝乳蛋白酶原 腸細胞 腸激酶 胰蛋白酶 胰凝乳蛋白酶 羧基端胜肽酶原 羧基端胜肽酶 Trypsinogen 胰蛋白酶原is converted to trypsin 胰蛋白酶 by the brush border enzyme enterokinase 腸激酶. Trypsin then converted other zymogens to their active forms in the lumen of the small intestine and also converts other trypsinogen to trypsin (not shown). Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P584-585 Absorption of amino acids and smaller peptides Once proteins are digested, amino acids are actively transported into intestinal epithelial cells 小腸上皮細胞 by cotransport with sodium across the apical membrane 頂端膜 There are at least four distinct amino acid carriers that can transport the 20 amino acids Absorption of amino acids Cross apical membrane by sodium-linked secondary active transport Cross basolateral membrane by facilitated diffusion Absorption of di- and tri-peptides Cross apical membrane by active transport Broken down inside cell to amino acids Amino acids cross basolateral membrane by facilitated diffusion P584 Lipids—digestion Lipids 脂質 consumed in the diet are primarily triglycerides 三酸甘油酯 (90%), with some phospholipids 磷脂質 and cholesterol 膽固醇 & other lipids enter the GI tract in secretions 分泌物, such as bile 膽汁 Lipids are digested by a class of enzymes called lipases 脂解酶: Lingual 舌的 lipase—an enzyme found in saliva digestion of lipid begins in the mouth and continues in the stomach Gastric 胃的 lipase—an enzyme secreted into the gastric lumen Pancreatic lipases 胰脂解酶—an enzyme secreted into the small intestine Because lipids are hydrophobic 舒水性, but lipases are water-soluble 水溶性 lipids do not mix readily with chyme form fat globules 脂肪球 Efficient digestion 有效率的消化 of lipids is made possible by the action of bile 膽汁 it simple facilitates the action of lipases by breaking fat globules down into smaller droplets 小顆粒, a process called emulsification 乳化作用 P584-585 Lipids—bile salts and emulsification Hydrophilic 脂肪球 (非極性) 舒水性 (非極性) 水(極性) Hydrophobic Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 親水性基團 (極性) 膽鹽 (兩極性) Emulsification 乳化作用 Figure 20.16 A representative bile salt. 脂肪油滴 (非極性) The emulsification 乳化作用 of fats is due to primarily to the action of bile salts 膽鹽 they are amphipathic 兩極性的 it endow the droplets with a polar “coating” that allows them to mix more reading with water and break down into smaller droplets P586 磷脂質 三酸甘油酯 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.17 Emulsification of a fat globule by bile salts. Lipids—the action of pancreatic lipase As fat is being emulsified 乳化 in the duodenum, it is also mixed with pancreatic lipase 胰脂解酶 a colipase 共同脂解酶 molecule (a peptide secreted in pancreatic juice) binds to a lipase molecule in a one-to-one fashion, allowing the lipase to interact with the fat globule and digest outer layers of lipids 消化外層的脂質 Triglyceride Lipase colipase Monoglyceride + 2 Fatty acids Figure 20.18 Liberation of fatty acids and monoglycerides from fat droplets by lipases. Note that these end-products of fat digestion aggregate into micelles 微膠粒, which are equilibrium with dissolved molecules. Some dissolved molecules (monoglyceride, fatty acid) cross the apical membranes of intestinal epithelial cells by simple diffusion. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P586 Lipids—enterohepatic circulation of bile salts 肝門靜脈 肝臟 膽囊 Figure 20.19 The enterohepatic circulation. Bile salts are absorbed in the ileum, return to the liver via the 微血管 circulation, and are eventually resecreted in the bile. 總膽管 膽鹽 十二指腸 迴腸 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P586-587 In the ileum 迴腸, the bulk of the bile salts that were secreted into the duodenum 十二指腸 (about 95%) are absorbed into the circulation these bile salts are eventually recycled by the liver and secreted again in the bile via a pathway referred to as the enterohepatic circulation 腸肝循環 Lipids—absorption Figure 20.20 Events in the absorption of fats. Fatty acids 脂肪酸 and monoglycerides 單酸甘油酯 absorbed into enterocytes 腸細胞 are synthesized into triglycerides, which are then packaged into chylomicrons 乳縻小滴. After exocytosis 胞吐 into interstitial fluid, chylomicrons enter the lymphatic system 淋巴系統 via lacterals 乳縻管 and eventually reach the general circulation 全身血液循環 Chylomicrons, which belong to a general class of particles known as lipoproteins 脂蛋白, cannot enter the bloodstream directly because they are too large to cross capillary walls 微血管壁 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P588 Absorption of vitamins Vitamins are organic molecules needed in small amounts for the normal physiological function of cells they consumed in their absorptive form, and do not undergo digestion 不需進行消化即可吸收 Hydrophobic or fat-soluble vitamins (A, D, E, and K) are absorbed by epithelial cells in parallel with lipids 脂溶性維他命與脂質走相同吸收路徑 Water-soluble vitamins (B, C) are absorbed by special transport proteins, with some requiring active transport, other facilitated diffusion Vitamin B12 cannot be absorbed by itself 自己不能被吸收 it can be absorbed only when bound to intrinsic factor 內生性因子, which is secreted into the lumen of the stomach by parietal cells Pernicious anemia 惡性貧血 which can result from a lack of vitamin B12 in the diet or a lack of intrinsic factor Fat-soluble vitamins (A, D, E, and K) absorbed with lipids (dissolve in lipid droplets, micelles, chylomicrons) Water-soluble vitamins (B, C) require special transport proteins Vitamin B12 absorbed only when bound to intrinsic factor P588 Absorption of minerals Na+, Cl-, K+ and HCO3 Most sodium enters the GI tract through secretions 分泌物 (80%), although some is ingested 攝取 daily Sodium (Na+) Solvent drag 拖 with water reabsorption in duodenum, jejunum Actively absorbed in jejunum, ileum, and colon Chloride (Cl-) Passively follows sodium absorption 被動性的跟隨鈉離子而吸收 (並非以被動擴散的方式吸收) electro-neutrality 電中性 Potassium (K+) Passively absorbed depending on electrochemical gradients Secreted when lumenal concentrations very low (<25 mM) Bicarbonate (HCO3-) Passively absorbed in jejunum Secreted exchange for chloride ions in ileum, and colon P588-590 Absorption of minerals Ca2+ & Fe2+ Calcium (Ca2+) is actively absorbed in duodenum and jejunum binds to brush border protein (calcium-binding protein 鈣結合蛋白) taken into epithelial cell by an unknown mechanism transported out of cell across basolateral membrane by Ca2+ pump 1,25-(OH)2 Vitamin D3 (Calcitriol) increases calcium absorption by increasing concentration of calcium-binding protein 維他命D藉由增加鈣結合蛋白的量來增加鈣的吸收 The absorption of iron (Fe2+), like that of calcium and vitamin B12, requires the aid of proteins 需要蛋白的幫助 transferrin 運鐵蛋白 secreted by enterocytes into lumen of small intestine transferrin binds iron transferrin-Iron complex binds to a receptor taken into cell by receptormediated endocytosis The iron is either stored in enterocyte as ferritin 鐵蛋白 or transported across the basolateral membrane into the blood transported in blood is carried by another form of transferrin P590 Absorption of water Water in GI tract 7 liters/day secretions from the stomach, intestine, and accessory glands 2 liters/day intake Absorption of water is critical to maintain normal fluid balance 維持體液的平衡 the absorption of water is passive and is driven by an osmotic gradient 滲透梯度 across the mucosal epithelium Sodium is especially important in the creation of this gradient 鈉離 子對此滲透梯度的產生是很重要的 because it is the most abundant of all solutes 含量最多的溶質 in the lumen 管腔 and in the interstitial fluid 間質液, and therefore makes the largest contribution to the osmotic pressure 產生滲透壓最大的貢獻者 P590 IV. General Principles of GI Regulation GI function not regulated based on concept of homeostasis 恆定 regulate GI function to maximize absorption, regardless of whether nutrients needed 胃腸道功能的調控並不是基於維持身體內在環境恆定的原則，而是 不管是否有所營養需求，竭盡所能的達到最大的吸收 GI functions are regulated by an impressive 印象深刻的 array of neural 神經的 and hormonal 賀爾蒙的 regulatory mechanisms, many of which involve negative feedback control 負回饋調控 P590 Neural and endocrine pathways of GI control GI function is under an elaborate 複雜的 control system involving the autonomic nervous system (ANS) 自律神經系統, enteric nervous system (ENS) 腸神經系統, and GI hormones secreted from the stomach and small intestine The ENS consists of its own sensory neurons 感覺神經, motor neurons 運動神經, and interneurons 中間神經元 influences of the ANS on GI functions are generally indirect, mediated via communication to the ENS 自律神經系統對胃腸功能的調控通常是間接的經由與腸神經系統的溝通來調控 Conditions in the lumen of the tract are monitored by three types of receptors neurons (sensory neuron) located within the GI wall 胃腸道管壁 內有三種感覺神經的接受器可偵測管腔內的情況 afferents from these receptors project to both the ENS and the CNS 訊息可傳送至ENS及中樞 Mechanoreceptors 機械性接受器, which detect the degree of distension of the wall 偵測管壁膨脹的程度 Chemoreceptors 化學接受器, which monitor the concentrations 濃度 in the lumen of specific substances such as hydrogen ions or fats Osmorecetprs 滲透性接受器, which monitor the osmolarity 滲透度 of the luminal contents P590 The ENS and CNS exert their control over GI function via neuron projecting to various types of effectors 作用者 in the GI organs, usually smooth muscle cells or secretory cells (which may be exocrine or endocrine) Once endocrine cell are stimulated, the hormones they secrete circulate in the bloodstream and eventually return to the GI system to exert their effects P590 胃泌素 膽囊收縮 素 腸促胰泌素 葡萄糖依賴型 促胰島素胜肽 Enterogastrones 腸抑胃素 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P591 Short and long reflex pathways Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 情緒狀態 長的反射路徑 食物的色、 香、味覺 短的反射路徑 Figure 20.21 P591 Signals may travel from receptors to the intrinsic nerve plexuses and then directly to the effectors, following what is called a short reflex pathway Signals may follow a long reflex pathway, traveling from receptors to the CNS and then to the intrinsic nerve plexuses, which relay 傳遞 information to the effectors Increased parasympathetic activity usually promotes an increase in GI activity, which is manifested as an increase in muscle activity or fluid secretion sympathetic activity generally inhibited the GI activity Phases of gastrointestinal control A given region of the GI tract can respond to stimuli arising either within that region or in more remote regions 每區段的胃腸道可對 此區段來的刺激或更遠處的刺激產生反應 Cephalic Phase 頭期—stimuli originate in head 頭 thoughts, taste, smell of food… requires input from CNS (long reflexes) Gastric Phase 胃期—stimuli originate in stomach 胃 via long and short reflex and GI hormones Intestinal Phase 腸期—stimuli originate in small intestine 小腸 via long and short reflex and GI hormones P591-592 Regulation of food intake Physiological regulation 生理性調控 of food intake can occur over the a meal because you are hungry 肌餓 and then stopping because your hunger has disappeared (satiety 飽足) short-term regulation Satiety factors 飽足因子 (such as insulin 胰島素, CCK 膽囊收縮素, neural input 感覺訊息的傳入 from mechanoreceptors 機械性接受器 and chemoreceptors 化學接受器) acts on the hypothalamus 下視丘 to reduce the sensation of hunger 減少飢餓的感覺 Increases in your daily food consumption over the weeks since you began an exercise program is an example of long term regulation Leptin 瘦素 is a hormone released from adipose cells 脂肪細胞 when calories exceeds demands 當卡洛里(熱量)超過身體所需 Leptin acts on appetite-control centers 飲食調控中樞 in the hypothalamus to reduce the sensation of hunger Leptin also promotes a general increases in the body’s metabolic rate 增加身體基礎代謝率, which reduces fat storage 減少脂肪儲存 P592 V. Gastrointestinal Secretion and Its Regulation Saliva Secretion 唾液的分泌 Acid and Pepsinogen Secretion in the Stomach 酸及胃蛋白酶在胃的分泌 Secretion of Pancreatic Juice and Bile 胰液及膽汁的分泌 Rates of Fluid Movement in the Digestive system 液體在消化系統的移動速率 Saliva Secretion Taste of food Chemoreceptors in taste buds 味蕾 Sight and smell of food Cerebral cortex 大腦皮質 Salivary center 唾液中樞 of medulla 延腦 Autonomic nervous system Stimulate salivation Saliva 唾液 secretion is stimulated by both parasympathetic 副交感的 and sympathetic 交感的 neurons Parasympathetic activity stimulates copious 大量的 secretion of a watery 水性的 saliva Sympathetic activity stimulates minute 少量的 secretion of proteinrich, viscous 黏性的 saliva P592 Acid Secretion in Stomach The acid secreted by the stomach is generated inside parietal cells by the reaction of carbon dioxide (CO2) with water (H2O), which is catalyzed by the enzyme carbonic anhydrase 碳酸酐酶 (CA) and generates hydrogen ions (H+) and bicarbonate (HCO3-) Carbonic Anhydrase CO2 + H2O H2CO3 HCO3- + H+ P592-593 Parietal cells produce acid by active transport of H+ into lumen of stomach & HCO3- transported into interstitial fluid in exchange for Cl- Cl- diffuses into lumen through channels H+ and Cl- secreted into lumen & HCO3- enters blood Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.22 Mechanism of gastric secretion. Note that because potassium ions are actively transported from the lumen into parietal cells and then passively leak back into the lumen, these ions are simply recycled across the apical membrane. Regulation of Acid and Pepsinogen Secretion into Stomach The secretion of acid by parietal cells is stimulated by parasympathetic nervous activity 副交感神經活性, gastrin 胃泌素, and histamine 組織胺, which is secreted by cells in the stomach lining 胃內層的細胞 and acts as a paracrine agent Acid secretion is controlled by cephalic-phase 頭期, gastric-phase 胃期, and intestinal-phase 腸期 stimuli and is generally stimulated when food is present in the stomach and suppressed when the food leaves Because the stimuli that affect acid secretion also tend to affect the secretion of pepsinogen in the same manner, the secretion of pepsinogen generally rises and falls in parallel with changes in acid secretion 刺激酸與胃蛋白酶原分泌的形式相同，所以酸分泌增加時， 胃蛋白酶原也跟著分泌增加 P593 Stimulation of Acid and Pepsinogen Secretion into Stomach 胃中的蛋白質及其被消化的產物；胃的擴張 食物的色、香、味覺；咀嚼及吞嚥 Reinforce 增強 Reinforce 增強 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.23 Regulation of gastric secretion P593 Reduction of Acid and Pepsinogen Secretion into Stomach As food leaves the stomach, both gastric-phase and intestinal-phase stimuli work to reduce acid and pepsinogen secretion exit of food removes stimuli for secretion 食物離開胃，刺激因子也跟著 移除 increased acidity inhibits gastrin release 因蛋白質(混合酸，蛋白質存在 時胃的酸鹼值提高))離開，胃的酸性增加，而抑制胃泌素的釋放(負回饋) The reduction in gastric secretion that occurs during gastric empting is also triggered by signals arising from the food into the duodenum entry of food into duodenum osmolarity; fat and acid; distension These changes stimulate chemoreceptors, osmoreceptors, and mechanoreceptors relay signals via long and short reflex pathways inhibit acid and pepsinogen secretion Signals relayed to the endocrine cells in the small intestine that secrete CCK, secretion, and GIP suppress the secretory activity of parietal and chief cells P594 Secretion of Pancreatic Juice Acinar cells 腺泡細胞 produce small volume of primary secretion with digestive enzymes & duct cells 管細胞 produce bicarbonate-rich fluid Enzyme and bicarbonate secretion regulated somewhat separate 分開的 composition of pancreatic juice 胰液 varies based on lumenal contents Figure 21.8 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. The strongest influences on pancreatic secretion are hormones CCK 膽囊收縮素 and secretin 腸促胰泌素, which are released in response to the presence of food in the duodenum CCK acts primarily on acinar cells to stimulate enzyme secretion, whereas secretin acts primarily on duct cells to stimulate the secretion of bicarbonate-rich fluid When CCK and secretin are both present, these hormone amplify each other’s effects 將另一個的作用放大, a phenomenon known as potentiation 強化作用 P594 Secretion of Pancreatic Juice The release of secretin 腸促胰泌素 and subsequent secretion of bicarbonate-rich fluid is strongly affected by the acidity 酸度 of the duodenal contents 十二指腸內容物 The secretion of CCK is regulated primarily by the concentration of protein digestion products 蛋白質消化產物 and fat 脂肪 in the duodenum, which rise as chyme leaves the stomach Stimuli for CCK release fat and protein digestion products in duodenum Stimuli for secretin release acidity in duodenum Figure 20.24 Stimulation of the secretion of bicarbonate-rich fluid by acidity in the duodenum. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P594-595 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Secretion of Bile CCK and secretin are also responsible for regulating the entry of bile into the duodenum Secretin acts on the liver to stimulate bile secretion 刺激肝臟分泌膽汁 CCK promote gallbladder contraction and relaxation of the sphincter of Oddi 促進膽囊收縮及歐迪士括約 肌鬆弛 Figure 20.25 The mechanisms by which secretin and CCK regulate the entry of bile into the duodenum. P595 Rates of Fluid Movements in the Digestive System Fluid entering lumen daily 9000 mL Figure 20.26 Approximate daily fluid flows in the gastrointestinal system. Fluid leaving lumen daily 8900 mL Amount excreted in feces = 9000 mL – 8900 mL = 100 mL Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P595 VII. Gastrointestinal Motility and Its Regulation Electrical Activity in Gastrointestinal Smooth Muscle 胃腸道平滑肌的電活性 Peristalsis and Segmentation 蠕動及分節運動 Chewing and Swallowing 咀嚼及吞嚥 Gastric Motility 胃的能動性 Motility of the Small Intestine 小腸的能動性 Motility of the Colon 結腸的能動性 Electrical Activity in GI Smooth Muscle In the muscularis mucosae 黏膜肌層 is a thin layer of longitudinal muscles and circular muscles that function to mix lumenal contents 混合管腔內容物 In the muscularis externa 外肌層 are two separate layers of smooth muscle the inner circular layer is capable of generating slow, spontaneous, grades 漸進性的 depolarizations 去極化 known as slow waves 慢波 When slow waves large enough to bring the membrane potential to threshold 閾值 are accompanied by action potentials 動作電位 In any given region of the GI tract, slow waves occur at regular 黏膜層 intervals 固定間隔 at a fairly constant frequency 幾乎固定的頻率, 黏膜下層 a pattern that is referred to as the basic electrical rhythm (BER) 外肌層 基礎電性節律 and is affected by 漿膜層 neural activity and hormones: parasympathetic excitation 黏膜 固有 層 Figure 20.3 黏膜肌 層 環狀肌 縱狀 肌 黏膜下神經叢 P596 腸肌神經叢 腸神經系統 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Electrical Activity in GI Smooth Muscle Neural activity and hormonal signals generally affect the height of slow waves rather than their frequency In the stomach, smooth muscle generates force in a grade fashion 漸進的形式 that varies according to the degree of depolarization 去極化 的程度 larger depolarizations trigger stronger contractions 收縮 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. In the intestines, no force is generated unless action potentials occur when action potentials do occur, the strength of contraction varies in a graded fashion with changes in the action potential frequency 收縮強度與動作電位發生 的頻率有關 Figure 20.27 Slow-wave electrical activity in gastrointestinal smooth muscle. Depolarizations that exceed threshold result in action potentials (top), inducing GI smooth muscle contractions whose strengths vary with the frequency of the action potentials (bottom). P596 Peristalsis and Segmentation The basic electrical rhythm (BER) set up a wave of contraction 收縮波 in the muscularis externa 外肌層 that travels longitudinally down the intestinal tract these waves called peristalsis 蠕動 Peristalsis propels the contents forward 推動內容物往前 at a rate dependent on the BER 推動的速率依BER而定 In the proximal 前端 GI segment circular muscle contracts; longitudinal muscle relaxes diameter decreases In the distal 遠端 GI segment circular muscle relaxes ; longitudinal muscle contracts diameter increases prepares it to receive the contents from the proximal segment 準備接收從前端送來的 內容物 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.28 Comparison of peristalsis and segmentation. (a) In peristalsis, waves of contraction travel a short distance and then die out, propelling the chyme along the GI tract’s path. P596-597 Peristalsis and Segmentation In the small intestine, the muscularis externa is also capable of segmentation 分節運動, alternating contractions 交替收縮 between intestinal segments that mix the chyme 混合食糜 In segmentation, while one segment of circular muscle in the intestine contracts, segments on either side relax, thereby allowing contents to move in both directions 讓內容物往兩端移動 from the contraction P597 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.28 Comparison of peristalsis and segmentation. (b) In segmentation, waves of contraction cause neighboring segments of intestine to contract and relax, mixing the chyme by shuttling it back and forth. Chewing and Swallowing Chewing 咀嚼 is like breathing 呼吸 in that it is controlled both consciously 意識的 and unconsciously 非意識的 We can control the rate and force of chewing motions voluntarily & unconscious chewing is orchestrated by a chewing reflex 咀嚼反射 Chewing reflex– cyclical reflex 週期性反射 normally, jaw muscles 顎肌 active hold mouth closed food enters mouth stimulate pressure receptor 壓力接受器 inhibits jaw muscles relax Jaw dropping relieves pressure of food 下顎往下解除食物造成的壓力 jaw muscles 顎肌 contract hold mouth closed Pressure from food restored 又恢復食物產生的壓力 inhibits jaw muscles Chewed food + saliva = bolus 食團 tongue 舌 moves bolus to pharynx 咽 initiates swallowing reflex 吞嚥反射, a series of muscle contractions coordinated by the swallowing center 吞嚥中樞 in the medulla 延腦 P597 Chewing and Swallowing Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 20.29 Events of the swallowing reflex. P598 Bolus descends in pharynx, pressing on epiglottis 會厭 epiglottis covers glottis 聲門 so food does not enter trachea inspiration 吸氣 inhibited Upper esophageal sphincter relaxes bolus enters esophagus sphincter closes behind bolus bolus stretches esophagus, triggering peristalsis Peristalsis propels bolus to stomach (~ 9 seconds) bolus arrives at stomach triggers relaxation of lower esophageal sphincter bolus enters stomach P597 Gastric Motility The muscle of the stomach accomplish two tasks: mix chyme 混合 食糜 & regulate gastric emptying 調節胃排空 are achieved by peristalsis & coordinated by ENS Peristaltic waves travel downward from the upper body of the stomach to the pylorus, normally at a rate of about 3次/min Each wave begins as a weak contraction but progressively increasing in force as it advances toward the pylorus As peristaltic waves increase in strength, they force the pyloric sphincter open as chyme is propelled forward into duodenum gastric emptying The force of gastric contraction increases in response to gastrin and decreases in response to CCK, secretin, and GIP The control of gastric motility is similar to the control of gastric secretion P598-599 Vomiting Certain conditions can cause the contents of the stomach and sometimes of lower portions of the GI tract to be forcefully expelled through the mouth, a phenomenon know as vomiting 嘔吐 Vomiting can be triggered by a variety of stimuli, including illness (such as influenza 流行性感冒), strong emotional states, severe pain, severe distension of the stomach or small intestine, rotational motion of the head (as in motion sickness 動暈症), or the ingestion of certain substances (such as copper sulfate) substances that stimulate vomiting are known as emetics 催吐劑 Vomiting involves a complex sequence of events (called the vomiting reflex) that is coordinated by a region in the medulla called the vomiting center P599 Motility of Small Intestine Like the stomach, the small intestine exhibits different patterns of motility depending on whether food is present or absent motility patterns also differ in the muscularis externa and muscularis mucosae When chyme is present in the small intestine, brief periods of peristalsis that propel the chyme forward are interspersed with relatively longer periods of segmentation that mix the chyme Segmentation, peristalsis, and migrating motility complexes result from the contractile activity of the external muscle layers, but the innermost layer (the thin muscularis mucosae) also undergoes regular contractions when food is present Contractions of the small intestine are influenced both by distension and by input from extrinsic nerves and hormones P599 Regulation of Motility of Small Intestine Distension – increases motility Autonomic nervous system Parasympathetic 副交感神經 excites Sympathetic 交感神經 inhibits Hormones – gastrin 胃泌素 stimulates motility Intestino-intestinal reflex 腸-腸反射 Ileogastric reflex 迴腸-胃反射 Injury or severe stress inhibits intestinal contractions Distension of ileum inhibits gastric motility Gastroileal reflex 胃-迴腸反射 Presence of chyme in stomach increases motility in ileum P599 Motility in Colon In the colon, contractile activity severs to mix the chyme which facilitates the absorption of minerals and water & to propel the lumenal contents toward the rectum for storage and eventual elimination The more proximal portions of the colon exhibit a pattern of motility called haustration 結腸袋 which is similar to segmentation 分節運動 in the small intestine — except that haustra are delineated by permanent folds in the intestinal wall and are regular in appearance — it also significantly slower than segmentation contractions occur at a rate of about two per hour 橫結腸 結腸袋 About three or four times a day, a different pattern of activity begins mass movement 整體移動 is like a peristaltic wave 蠕動波, except that a given portion of the intestine contracts, it remains contracted a longer time before relaxing Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P599-600 Motility in Colon Purpose: mix 混合 and propel 推進 Haustrations: mix Proximal colon Like segmentation, but slower Mass Movement: propel Similar to peristalsis Contraction lasts longer than relaxation Move bolus toward rectum Colonocolonic reflex 結腸-結腸反射: Distension of colon in one area causes relaxation of other areas of colon Gastrocolic reflex胃-結腸反射: Food in stomach increases colonic motility P600 Defecation Distension of colon Stretch receptors Rectum smooth muscle contracts Involuntary control 不隨意控制 Increase pressure in rectum Internal anal sphincter relaxes Both sphincters relax External anal sphincter contracts Defecation 排便 Voluntary control 隨意控制 P600
