Human Nutrition Notes PDF

6 Nutrition in humans 人的營養 Curriculum and Assessment Guide課程及評估指引 Students should learn Students should be able to Suggested Learning and Teaching Activities 學生應學習 學生應...

6 Nutrition in humans 人的營養 Curriculum and Assessment Guide課程及評估指引 Students should learn Students should be able to Suggested Learning and Teaching Activities 學生應學習 學生應能 建議學與教活動 III Organisms and Environment 生物與環境 b. Essential life processes in animals 動物維持生命的活動 Nutrition in humans 人的營養  Ingestion 攝食 Dentition 齒系 Mastication 咀嚼  Digestion 消化  Explain the significance of mechanical and  Examine the alimentary canal and its General plan of the digestive system 消 chemical digestion.解釋機械消化及化學消 associated glands of a dissected mammal or 化系統的一般結構 化的重要性。 a human torso.檢視一已解剖哺乳動物或人 Digestion of carbohydrates, proteins  Understand the digestion and absorption 體模型的消化道及其附屬腺體。 and lipids in various parts of the processes in various parts of the alimentary  Perform practical work to demonstrate the alimentary canal 碳水化合物、蛋白質 canal.了解消化道各部分的消化和吸收過 effect of bile salt on oil.進行實驗，顯示膽鹽 和脂質在消化道各部分的消化 程。 對油的效應。  Absorption and assimilation 吸收和同化  Illustrate the adaptive features of the small  Design and perform investigations to study Structural adaptation of small intestine intestine for food absorption.說明小腸在食 the action of digestive enzymes (e.g. for food absorption 小腸吸收食物的構 物吸收的適應特徵。 amylase on starch-agar plate, protease on 造特徵  Describe the routes of the transport of milk-agar plate or egg white).設計及進行探 Role of liver 肝的角色 absorbed food and their fates in cells and 究實驗，研究消化酶的作用（例如澱粉酶 Fate of absorbed food 食物被吸收後的 tissues.描述吸收後食物物質的轉運途徑及 於澱粉瓊脂平板的作用，蛋白酶於奶瓊脂 去向 其在細胞與組織內的去向。 平板或蛋白的作用）。  Perform practical work to simulate digestion and absorption in the alimentary canal using dialysis tubing.進行實驗，使用透析管，模 擬消化道內的消化和吸收。  Egestion 排遺 6-1 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.1The process of human nutrition 人的營養過程  Nutrients are required for the maintenance of life in organisms.營養素是生物維持生命所 必須的。  Nutrition is the process by which organisms obtain food substances to maintain life.營養作 用是指生物獲取及使用營養素的整個過程。  Modes of nutrition refers to the different methods through which organisms obtain food.營 養方式是指生物獲取營養素的各種不同方法。  There are two different modes of nutrition, namely autotrophic nutrition and heterotrophic nutrition.營養方式有兩種，自養營養及異養營養。  Humans are heterotrophs. They feed on other organisms for food.人是異養生物，透過攝食其他生 物來獲取食物。  Nutrition in human consists of five main process 人的營養作用包括五個階段： 1. Ingestion: The intake of food into the mouth and then into the alimentary canal.攝食：把食物放 進口腔，然後進入消化道。 2. Digestion: The breakdown of food inside the alimentary canal into small, simple and soluble molecules for absorption.消化：食物在消化道內分解成細小、簡單和可溶的分子，以供身 體吸收。 3. Absorption: The passage of digested food through the wall of the alimentary canal into the circulatory system. It is then transported by blood and lymph to different parts of the body.吸收： 已消化的食物穿過腸壁進入循環系統，然後經由血液及淋巴帶往身體各部份。 4. Assimilation: The entry of absorbed food into cells and use for metabolism.同化：已吸收的食 物分子由細胞吸收，用於新陳代謝。 5. Egestion: The removal of undigested and unabsorbed food from the body as faeces.排遺：將不 能消化及不能吸收的物質以糞便的形式排出體外。 食物 Food 攝食 Ingestion 消化 Digestion 吸收、同化 Absorption, Assimilation 排遺 Egestion 6-2 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.2 The human digestive system 人的消化系統  The human digestive system consists of the alimentary canal and its associated glands.人的消化系 統由消化道及其附屬腺體組成。  The alimentary canal consists of: mouth cavity → Pharynx → Oesophagus → Small intestine (duodenum → ileum) → Large intestine (caecum + appendix → colon → rectum) → Anus 消化道包括：口腔 咽 食道 胃 小腸（十二脂腸 迴腸） 大腸（盲腸＋闌 尾 結腸 直腸） 肛門  The associated glands include: salivary glands, pancreas and liver.附屬腺體包括：唾腺、胰和肝 口腔 Mouth 牙齒 Teeth 舌頭 Tongue 咽 Pharynx 唾腺 Salivary gland 食道 Oesophagus 胃 Stomach 肝 Liver 膽囊 Gall bladder 胰 Pancreas 小腸 Small intestine 十二指腸 Duodenum 大腸 Large intestine 結腸 Colon 迴腸 Ileum 盲腸 Caecum 闌尾 Appendix 直腸 Rectum 肛門 Anus The human digestive system 人的消化系統 6-3 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.3 Ingestion of food 食物的攝食  Food is taken into the alimentary canal through the mouth. Food is chewed/masticated by teeth into small pieces. Chewing facilitates swallowing. It also increase the surface area of the food for enzyme digestion.食物從口進入消化道。在口腔，食物由牙齒咀嚼成小塊。咀嚼有助吞嚥，亦可增加食 物可供酶進行消化作用的表面積。 A What types of teeth do we have ?牙齒有哪些種類？  Mammals have four different types of teeth for different functions.哺乳動物有四種不同類型的牙 齒，用以執行不同功能。 牙齒的種類 特徵 功能 Types of teeth Features Function Incisor  At the front of the jaw.位於顎骨的前  For biting and cutting food. 門齒 端。 咬斷和切割食物。  Chisel-shaped, with sharp edges (well-developed in herbivores).外形像鑿 子，邊緣鋒利。（在草食性動物十分發 達）  Has one root.只有一個齒根。 Canine  Located next to the incisors.位於門齒旁  For killing prey and tearing 犬齒 邊。 flesh.殺死並把獵物的肉塊  Pointed and curved backward 撕開。 (well-developed in carnivores, usually absent in herbivores).呈錐形，較尖銳， 微向後彎曲（在肉食性動物十分發達， 通常不存在於草食性動物）。  Has one root.只有一個齒根。 Premoloar  At the sides of the jaw.位於顎的兩側。  For grinding and crushing 前臼齒  Broad top with cusps.齒面闊而有尖突。 food.磨碎和壓碎食物。  Has one or two roots.有一個或兩個齒  In carnivores, they can be 根。 used to crush bones.在肉食 6-4 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  Molar  At the rear end of the jaw.位於顎的後 性動物，可把骨壓碎。 臼齒 方。  In herbivores, they are used  Similar to premolar but larger.與前臼齒 to grind plant materials.在草 相似，但體積較大。 食性動物，可把植物磨碎。  Has two or three roots.有兩個或三個齒 根。 B What is the structure of a tooth ?牙齒的構造是怎樣的？ The vertical section of a molar 臼齒的縱切面 結構 Structure 特徵 Feature  It is the outermost, hardest region of the crown.齒冠的最外部，是牙 齒最堅硬的地方。 Enamel  It is non-living and is made mainly of calcium phosphate.沒有生命， 琺瑯質 主要成分是磷酸鈣。  It protects the teeth against wearing.保護牙齒免受磨損。  It is the middle region of a tooth. It is not as hard as the enamel.牙齒 Dentine 的中部。硬度不及琺瑯質。 牙本質／象牙質  It has strands of living cytoplasm and nerve endings.內含一束束的活 細胞質及神經末梢。  It contains living cells.含有活細胞。  Blood vessels supply oxygen and nutrients to the teeth and remove Pulp cavity waste.血管為牙齒供應氧和營養素，並帶走代謝廢物。 髓腔  The nerve endings can detect temperature and pressure changes.神經 能探測溫度和壓力變化。 Cement and Periodontal  They fix the tooth to the jawbone.把牙齒固定在顎骨內。 membrane 牙骨質和牙周膜 6-5 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  C What is the dentition of humans ?人的齒系是怎樣的？  Dentition refers to the number and arrangement of different types of teeth in a mammal.齒系是指哺 乳動物各種牙齒的數目和排列方式。  It can be represented by a dental formula. It shows the number and types of teeth on one side of the upper and lower jaw.齒系通常以齒式表示。它顯示上、下顎一側的牙齒數目和種類。  Dentition is closely related to diet.齒系與膳食有著密切關係。 e.g. herbivores feed on plants, their teeth are adapted to cutting and grinding of plant tissues.例 如：草食性動物只吃植物，牠們的牙齒適應於切割及研磨植物組織。 e.g. carnivores feed on animal, their teeth are adapted for killing prey, tearing off flesh and crushing bones.例如：肉食性動物主要吃動物，牠們的牙齒適應於捕殺獵物、撕開肉類和 壓碎骨骼。 2 1 2 3 2123 i , c , pm , m  The dental formula of human adult is 2 1 2 3 or simply 2123 成 人 的 齒 式 是 2 1 2 3 2123 i , c , pm , m 2 1 2 3 或簡化為 2123 。  Not all mammals possess all four types of teeth, the arrangement of teeth in the upper jaw and lower jaw may differ.並非所有哺乳動物都擁有全部四種牙齒，上顎牙齒的排列也不一定與下顎的一 樣。 D What are milk and permanent teeth ?甚麽是乳齒和恆齒？ 乳齒 Milk teeth 恆齒 Permanent teeth Description  It appears during the first 2  Between the age of 6-12, it 描述 years of life. Between the age of gradually replace the milk teeth. 6-12, the milk teeth gradually Once lost, there will not be any fall off.由出生後至兩歲期間長 replacements.在 6 至 12 歲期間 出，在 6 至 12 歲期間會逐漸脫 取代乳齒。一旦脫落，不會再 落。 有新的牙齒長出補替。  Milk teeth has no premolar and  The last molar is also called the fewer molars.沒有前臼齒及較 wisdom teeth.位於最後的一顆 少臼齒。 臼齒，又稱為智慧齒。 Dental formula 2102 2123 齒式 2102 2123 Total number of teeth 20 32 牙齒總數 乳齒 Milk teeth 恆齒 Permanent teeth 6-6 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.4 Movement of food along the alimentary canal 食物在消化 道中的移動 1 Swallowing 吞嚥  After being chewed by teeth into small pieces, food will then e swallowed into the oesophagus.食物 被牙齒咀嚼成小塊後，會被吞嚥到食道。  Before swallowing, the tongue mixes the food with saliva and shapes the food into a bolus.吞嚥前， 舌頭把食物與唾液混合，形成柔軟的食團。  The swallowing process：吞嚥的過程： 1. The tongue rises and push the bolus towards the 鼻腔 pharynx.舌頭提高，把食團向後推向咽。 Nasal 2. The bolus push the soft palate upward, to prevent the cavity bolus from entering the nasal cavity.食物把軟腭向 上推，防止食團進入鼻腔。 3. The larynx rises so that the epiglottis covers the 舌頭 opening of the trachea. This prevents the bolus from Tongue entering the trachea.喉部上升，會厭覆蓋氣管入 口，防止食團進入氣管。 4. The bolus enters the oesophagus.食團進入食道。 氣管 Trachea 2 Peristalsis 蠕動  After being swallowed, peristalsis of the intestine pushes the food towards the anus. 縱肌 吞嚥後，消化道的蠕動把食物在消化道內 longitudinal 向前推進直至肛門。 muscle  Peristalsis also helps in breakdown of food 環肌 and mixes it with digestive juice to speed circular muscle up digestion.蠕動亦有助把食物搓爛，與消 管腔 化液混合，從而加速消化。 lumen Structure of the intestinal wall 消化道壁的結構  Peristalsis is the rhythmic contraction and relaxation of the muscles in the wall of the alimentary canal resulting in a wave-like action.蠕動是消化道壁的肌肉有節奏地收縮和放鬆，形成波浪式 的動作。  At the rear end of the bolus, the circular muscle contract, while the longitudinal muscle relax. The lumen constrict and the bolus is squeezed forward.在食團的後方，環肌收縮，縱肌放鬆，管腔 收窄，把食物推向前。  At the front end of the bolus, the circular muscle relax, while the longitudinal muscle contract. The lumen dilate and the bolus is allowed to slide forward.在食團的前方，環 肌放鬆，縱肌收縮，管腔擴張，讓食物通 過。 6-7 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.5 Digestion of food 食物的消化 A Why is digestion necessary ?為甚麼食物要經過消化？  Our food is made up of complex and large organic molecules. They cannot pass through the differentially permeably intestinal wall into the circulatory system.我們的食物普遍含有構造複雜 及巨大的有機分子，它們不能穿過具差異透性的消化道壁進入循環系統。  Food (like polysaccharides, disaccharides, protein, lipid) must be digested into small, simple and soluble molecules before they can be absorbed by the body into the circulatory system.食物（如多糖、 雙糖、蛋白質、脂質）必須先經消化分解成細小、簡單和可溶的分子，才可被身體吸收，進入 循環系統。  Monosaccharides, vitamins, minerals and water can be absorbed directly as their molecules are small. 至於單糖、維生素、礦物質和水的分子則較細，可以直接吸收。 B What is mechanical and chemical digestion ?甚麼是機械和化學消化？ 1 Mechanical digestion 機械消化  Mechanical digestion is the breakdown of food into small pieces by physical actions.機械消化是指 利用機械動作把食物變成碎塊的物理過程。  Mechanical digestion can increase the surface area of food in contact with digestive juice, but it does not alter its chemical structure. Products of mechanical digestion still cannot be absorbed by the intestine. It includes：它可增加食物與消化液接觸的表面積，但不會改變食物的化學成分。機 械消化後的產物仍然未能被腸道吸收。它包括： 1. Chewing/mastication of food by teeth into small pieces inside the mouth.口腔內牙齒的咀嚼把 食物嚼成小塊。 2. Churning action of the stomach and peristalsis along the alimentary canal can breakdown food. 胃的劇烈攪動與及消化道的蠕動把食物搓爛。 3. Emulsification of lipid by bile salt in the small intestine.小腸內膽鹽把脂質乳化成細小的油微 滴。 2 Chemical digestion 化學消化  Chemical digestion is the breakdown (hydrolysis) of complex food by digestive enzymes into small, simple and soluble molecules. The products of chemical digestion can be absorbed into the circulatory system.化學消化是指利用消化酶來把複雜的食物，分解（水解）成細小、簡單和可 溶的分子的化學過程。化學消化後的產物可被腸道吸收。 1. Carbohydrases: breakdown carbohydrates into disaccharides and monosaccharides.碳水化合物 酶：把碳水化合物分解成雙糖或單糖。 2. Protease: breakdown protein into polypeptides, peptides and amino acids.蛋白酶：把蛋白質分 解成多肽、肽和氨基酸。 3. Lipases: breakdown lipids into fatty acids and glycerols.脂肪酶：把脂質分解成脂肪酸和甘 油。 C How is food digested in the mouth ?食物在口腔內怎樣被消化？  Inside the mouth, chewing action of the teeth and digestive action of saliva helps in food digestion. 牙齒的咀嚼和消化液唾液的作用，把食物消化。  Saliva is secreted by the salivary gland, it contains：唾液由唾腺分泌。它含有： 6-8 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  成分 Ingredients 功能 Function Amylase  Under alkaline condition, amylase digest starch into maltose. 澱粉酶 在微鹼下，催化澱粉分解成麥芽糖的反應。  It binds food particles together.把食物碎塊黏在一起。 Mucus  It lubricates food and helps in chewing and swallowing.潤滑 黏液 食物，幫助咀嚼和吞嚥。 D How is food digested in the stomach ?食物在胃內怎樣被消化？  The stomach is a muscular bag.胃是一個由肌肉組成的囊狀器官。 食道 Oesophagus 賁門括約肌 cardiac sphincter 幽門括約肌 Pyloric sphincter 十二指腸 Duodenum Structure of the stomach 胃的結構  The stomach wall has gastric glands which secrete gastric juice which contains：胃液由胃壁上的胃 腺分泌。它含有： 成分 Ingredients 功能 Function Protease  Under strongly acidic condition, it digests protein into peptides. 蛋白酶 在強酸下，催化蛋白質分解成肽的過程。  It provides an acidic medium (~pH2) for protease to function.提 Hydrochloric acid 供酸性環境（~pH 2），讓蛋白酶發揮作用。 氫氯酸  It kills most bacteria in food.殺死食物中大部分細菌。  It protects the stomach from being digested by protease and Mucus being damaged by hydrochloric acid.保護胃壁，免受蛋白酶和 黏液 氫氯酸的傷害。  Churning action of stomach and digestive action of gastric juice will digest food into a semi-solid paste (chyme) which will then be released into the duodenum.胃的攪動和胃液的作用，把食物消化， 形成半固體狀的食糜。食糜隨後會進入十二脂腸。 E How is food digested in the small intestine ?食物在小腸內怎樣被消化？ 1 Bile 膽汁  Bile is secreted by the liver and temporarily stored in the gall bladder. Bile can be released through the bile duct into the duodenum. It contains：膽汁由肝分泌，並暫時儲存在膽囊中。膽汁經膽管 流入十二指腸。它含有： 6-9 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  成分 Ingredients 功能 Function  It emulsifies lipid into oil droplets which can increase the Bile salt (not an enzyme) surface area of lipid for lipase to act on.把脂質乳化為油微 膽鹽（並非酶！） 滴，用以增加它們可供脂肪酶作用的表面積。  It is the metabolic waste produced by the liver in the breakdown Bile pigment haemoglobin. It colours the faeces brown.是肝在分解血紅蛋白 膽色素 時所產生的代謝廢物，能把糞便染成褐色。  It neutralises the acidic chyme and provides an alkaline medium Sodium bicarbonate needed for the action of enzymes in the intestine.中和酸性的食 碳酸氫鈉 糜。提供鹼性環境，讓其他腸道內的消化酶發揮作用。 Experiment: Demonstration of the effect of bile salts on oil 實驗：顯示膽鹽對油的效應  Add bile salts into oil and shake well.將膽鹽溶 液加進油內並搖勻。  Bile salt can lower the surface tension of lipid, causing lipid to break physically into small oil droplets, forming an emulsion.膽鹽能減低脂質 的表面張力，使油乳化成細小的油微滴，成為 乳狀液。 2 Pancreatic juice 胰液  Pancreatic juice is secreted by the pancreas. It travels along the pancreatic duct into the duodenum. It contains：胰液由胰分泌，經胰管流入十二指腸。它含有： 成分 Ingredients 功能 Function Amylase  It digests the remaining starch into maltose.催化餘下的澱粉分 澱粉酶 解成麥芽糖。 Protease  It digests protein into peptides and peptides into amino acids.催 蛋白酶 化蛋白質分解成肽，並催化肽分解成氨基酸。 Lipase  It digests lipids into glycerols and fatty acids.催化脂質分解成 脂肪酶 甘油和脂肪酸。  It neutralizes the acidic chyme and provides an alkaline medium Sodium bicarbonate needed for the action of enzymes in the intestine.中和酸性的食 碳酸氫鈉 糜。提供鹼性環境，讓其他腸道內的消化酶發揮作用。 3 Intestinal juice 腸液  Intestinal juice is secreted by the glands in the intestinal wall. It is alkaline and contains mucus.腸液 由小腸壁上的腸腺分泌，呈鹼性，內有黏液。  Specialized cells on the wall of the intestine have the following enzymes on their cell membrane for food digestion：小腸壁上的特化細胞的細胞膜附有以下的酶以消化各種食物： 6-10 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  成分 Ingredients 功能 Function  Digest disaccharides into monosaccharides.催化雙糖分解 Carbohydrases (e.g. sucrase, 成單糖。 maltase) e.g. sucrose  (sucrase) glucose + fructose 碳水化合物酶（例如：蔗糖 例如：蔗糖 （蔗糖酶） 葡萄糖＋果糖 酶、麥芽糖酶） e.g. maltose  (maltase) glucose 例如：麥芽糖 （麥芽糖酶） 葡萄糖 Protease  Digest peptides into amino acids.催化肽分解成氨基酸。 蛋白酶  It neutralizes the acidic chyme and provides an alkaline Sodium bicarbonate medium needed for the action of enzymes in the intestine. 碳酸氫鈉 中和酸性的食糜。提供鹼性環境，讓其他腸道內的消化 酶發揮作用。 F What will happen to the food inside the large intestine ?食物在大腸內會怎樣？  After passing through the small intestine, digestion is basically completed.食物通過小腸後，消化已 大致完成。  Colon and rectum can absorb water, affecting the water content of faeces.結腸及直腸能吸收水份， 影響糞便的水份含量。  Colon will also be responsible for some of the mineral and vitamin absorption.部份礦物質及維生素 亦會經結腸吸收。  Caecum in human is very small and with no obvious function. Caecum in herbivores (e.g. rabbit) is large and well-developed. The caecum of herbivores can store a large amount of undigested cellulose. The symbiotic bacteria inside the caecum can secrete cellulase to digest cellulose. The sugar produced can be used by the bacteria and the herbivores.盲腸在人體內非常細小，功用並不明確。 但盲腸在草食性動物（例如兔）體內則頗大及發展良好。草食性動物的盲腸能貯存大量未被消 化的纖維素。盲腸內含共生細菌。這些細菌能分泌纖維素酶來消化纖維素，所產生的糖可供細 菌及動物本身吸收使用。  Faeces will be temporarily stored inside the rectum before egestion.在糞便排出體外之前，會暫存 在直腸內。 6-11 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  G Summary of chemical food digestion 食物的（化學）消化一覽 其他 消化液來源 作用部位 分泌 酶 成分 酸鹼值 消化作用 Source of Action location Secretions Enzymes Other pH Digestive action digestive juice ingridents Buccal cavity Salivary gland Salivary juice Amylse Mucus Alkaline Starch  (Amylase) → Maltose 口腔 唾腺 唾液 澱粉酶 黏液 微鹼 澱粉 （澱粉酶）→ 麥芽糖 Hydrochloric acids Stomach Gastric glands Stomach juice Protease Acidic Protein  (Protease) → Peptide 氫氯酸 胃 胃腺 胃液 蛋白酶 酸性 蛋白質 （蛋白酶） 肽 Mucus 黏液 Bile salt 膽鹽 Lipid  (Bile salt) → Emulsify lipid into oil droplets Bile pigment Liver Bile juice Nil (a type of mechanical digestion) 膽色素 肝 膽汁 無 脂肪 （膽鹽） 乳化成油微滴 Sodium （屬機械消化） bicarbonate 碳酸氫鈉 Starch  (Amylase) → Maltose Amylase 澱粉 （澱粉酶）→ 麥芽糖 Small intestine Alkaline 澱粉酶 Lipid  (Lipase) → Fatty acid + glycerol 小腸 Pancreatic Sodium 鹼性 Pancreas Lipase 脂肪 （脂肪酶）→ 脂肪酸＋甘油 juice bicarbonate 胰 胰液 脂肪酶 碳酸氫鈉 Protein  (Protease) → Peptide Protease 蛋白質 （蛋白酶） 肽 蛋白酶 Peptide  (Protease) → Amino acids 肽 （蛋白酶） 氨基酸 Intestinal glands Carbohydrases Sodium Disaccharides  (Carbohydrases) → Monosaccharides and specialized Intestinal juice 碳水化合物酶 bicarbonate cells 雙糖 （碳水化合物酶） 單糖 腸液 Protease 碳酸氫鈉 腸腺及特化細胞 蛋白酶 Mucus Peptide  (Protease) → Amino acids 6-12 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  黏液 肽 （蛋白酶） 氨基酸 6-13 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途 6.6 Absorption of digested food 已消化食物的吸收  Food absorption takes place mainly in the villi of ileum.食物的吸收主要在迴腸（的絨毛）中進行。 How is the small intestine adapted for food absorption ?小腸有哪些適應食物吸收的構造特 A 徵？  The small intestine is very long. It allows sufficient time for food digestion and absorption.小腸很長， 讓人體有足夠的時間把食物消化和吸收。  The intestinal wall is highly folded and has many finger-like projections called villi. Villi provide a large surface area for food absorption.小腸內壁高度摺疊，壁上還有很多手指狀的突出物，稱為 絨毛。這能提供一個大的表面積供吸收食物之用。 Cross-section of small intestine Longitudinal-section of a villus 小腸的橫切面 絨毛的縱切面  Adaptation of villi for food absorption：絨毛對食物吸收的適應特徵： 適應特徵 Structural adaptation 重要性 Importance 1. Finger-like (with many micro-villi on its  Increase the surface area for food absorption. epithelium)手指狀（上皮更有很多微絨毛） 增加表面積以吸收食物。 2. Thin epithelium which is only one cell  Shorten the distance for diffusion, to speed up thick 上皮很薄，只有一層細胞的厚度 food absorption.縮短擴散的距離，加快吸收。 3. Has a lacteal and a network of blood  To transport the absorbed food away rapidly, so capillaries 有乳糜管和微血管網 as to maintain a steep concentration gradient to 6-14 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  facilitate diffusion.能迅速把已吸收的食物分 子運離，保持陡峭的濃度梯度，加快吸收。 4. Peristalsis of the small intestine causes the  To ensure that the villi are always in contact villi to move.小腸的蠕動使絨毛移動。 with the digested food so as to maintain a steep concentration gradient to facilitate diffusion.使 絨毛表面經常接觸新近消化的食物，保持陡 峭的濃度梯度，加快吸收。 B How is digested food absorbed ?身體怎樣吸收已消化的食物？ 經血液吸收 經淋巴吸收 Absorption into the blood Absorption into the lymph Food  Monosaccharides, amino acids,  Fatty acids, glycerol and fat-soluble substance minerals, water-soluble vitamins and vitamins.脂肪酸、甘油和脂溶性維 食物物質 water.單糖、氨基酸、礦物質、水 生素。 溶性維生素和水。 Process  Food substances are absorbed into  Fatty acids and glycerol diffuse into 過程 the blood capillaries of villus by the epithelial cells and recombine diffusion and active transport.食物 into lipid molecules before they are 物質藉擴散和主動轉運（例如氨基 absorbed into the lacteal.脂肪酸和 酸、葡萄糖），吸收到絨毛的微血 甘油藉擴散吸收入絨毛的上皮細 管內。 胞，並重新合成為脂質，再被吸收 入乳糜管。 Route of  Capillaries of villus Hepatic  Lacteal of villus Main lymphatic transportation portal vein  Liver Hepatic vein duct Anterior vena cava Heart 運輸途徑 Posterior vena cava  Heart All parts of the body All parts of the body 絨毛乳糜管 → 主淋巴管 → 血 絨毛微血管 → 肝門靜脈 → 肝 管（前腔大靜脈） → 心 → 身體 → 肝靜脈 → 後腔大靜脈 → 心 各部分 → 身體各部分 6-15 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  6-16 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  Transverse section of villus showing food absorption 顯示食物吸收過程的絨毛橫切面 肝靜脈 Hepatic vein 心 Heart 肝 Liver 單糖、氨基酸、礦 淋巴管 物質和水溶性維 肝門靜脈 Lymphatic duct 生素和水 Hepatic portal 身體各部分 Monosaccharides, vein all parts of the body amino acids, minerals and 絨毛 脂質分子 Lipid molecule water-soluble Villus vitamins and water Transport of digested food from the villi to different parts of the body. 已消化食物從小腸輸送至身體各部分的途徑  Most of the water is absorbed in the stomach and small intestine by osmosis. Only a small amount is absorbed by the large intestine.食物中大部分水份藉滲透在胃和小腸內吸收，只有小部分在大腸 內吸收。  When digested food is being absorbed into the blood, it increases the water potential inside the lumen of the intestine, further enhancing the absorption of water in the small intestine.當小腸吸收 已消化食物進入血液時，間接增加了腸腔內的水勢，結果是進一步促進小腸吸收水份。 Experiment: Simulation of digestion and absorption in the small intestine using dialysis tubing.實驗：使 用透析管模擬消化道內的消化和吸收  Starch and saliva was mixed inside a dialysis tubing.將澱粉溶液及唾液在透析管內混和。  The outside of the dialysis tubing was washed with water. The dialysis tubing was then immersed in a water bath of 37℃and allowed to settle for some time.用清水沖洗透析管外壁。然後把透析管浸 入 37℃的水中，並靜置一段時間。  After a certain period of time, reducing sugar (Benedict’s test) was discovered in the water surrounding the dialysis tubing, but no starch (iodine test) was found.及後在透析管外的水中發現 還原糖（本立德試驗），但未能發現澱粉質（碘液測試）。  Since starch molecules are too large, they cannot pass through the dialysis tubing into the surrounding water.由於澱粉粒子太大，因 此未能通過選透性的透析管進入水中。  Salivary amylase digests starch into small maltose molecules. Maltose (reducing sugar) can pass through the dialysis tubing into the surrounding water.澱粉被唾液中的澱粉酶消化成細小的麥 芽糖分子，麥芽糖（還原糖）能通過選透性的透析管進入水浴 中。  The experiment simulated the digestion and absorption inside the small intestine. The dialysis tubing represents the alimentary canal.這實驗模擬了人類消化管內的消化和吸收作用。透析管 代表消化管。透析管外的水代表血液。  We can use boiled saliva instead of fresh saliva to set up a control experiment for the above studies. 6-17 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  可利用經煮沸之唾液為上述之消化作用實驗部分設置一對照實驗。  We can use PVC tubing (impermeable) instead of dialysis tubing to set up a control experiment for the above studies.可利用 PVC 膠管（不透性）取代透析管為上述之吸收作用實驗部分設置一對 照實驗。  Since human intestine is differentially permeable. The above studies showed that large food particles must be digested into small particles before they can be absorbed by intestine into the circulatory system.由於人類的腸道是差異透性的，因此上述實驗證明了必須把大的食物粒子消化成細小 的粒子，方能把它們經腸道吸收進血液之內。 6.7 Assimilation of absorbed food 已吸收食物的同化  Assimilation is the entry of food particles into cells for cell metabolism.同化是指細胞攝取並運用 已吸收食物分子，進行新陳代謝的過程。 A What are the fates of absorbed food ?已吸收食物在細胞內有甚麼去向？ 同化方式 Assimilation Glucose  Please refer to notes on Chapter 5, section 5.2 B1 on "Functions of 葡萄糖 carbohydrates" and "Fate of excess carbohydrates in human body".詳情請參閱 第 5 章 5.2 B1，有關「碳水化合物的功能」和「過量碳水化合物在人體的 去向」之筆記。 Lipid  Please refer to notes on Chapter 5, section 5.2 B2 on "Functions of lipids" and 脂質 "Fate of excess lipids in human body".詳情請參閱第 5 章 5.2 B2，有關「脂質 的功能」和「過量脂質在人體的去向」之筆記。 Amino acids  Please refer to notes on Chapter 5, section 5.2 B3 on "Functions of proteins" 氨基酸 and "Fate of excess proteins in human body".詳情請參閱第 5 章 5.2 B3，有關 「蛋白質的功能」和「過量蛋白質在人體的去向」之筆記。 B What are the roles of liver ?肝在同化中的角色是甚麼？ Liver has the following functions in assimilation：肝在同化中有以下的功能：  Regulation of blood glucose level by interconversion between glucose and glycogen. (please refer to notes on Chapter 18, section 18.2)通過葡萄糖和糖原的轉換來調節血糖水平。（詳情請參閱第 18 章 18.2 之筆記） If the glucose level is higher than normal 如血糖水平過高 1. After meal, a lot of digested glucose will be absorbed into the blood.飯後有大量已消化的葡萄 糖被小腸吸收進入血液。 2. This will increase the blood glucose level to higher than normal (especially in the hepatic portal vein leading to the liver)這會將血糖水平提升至高於正常水平（特別是通往肝臟的肝門靜 脈）。 3. High blood glucose level will stimulate pancreas to secrete more insulin and fewer glucagon.高 血糖水平會刺激胰臟分泌較多胰島素，但較少高血糖素。 4. Insulin stimulate body cells to absorb and utilize more glucose.胰島素會刺激體細胞吸收及使 用更多葡萄糖。 5. Insulin will stimulate liver cells to convert excess glucose into glycogen.胰島素會刺激肝細胞 6-18 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途  將過量的葡萄糖轉化成糖原。 6. Glycogen will be stored inside liver and muscle. It will lower the blood glucose level back to normal.糖原將貯存於肝臟及肌肉內。這過程將血糖降至正常水平。 If the blood glucose level is lower than normal 如血糖水平過低 1. During starving, blood glucose level will be lower than normal.在飢餓時，血糖水平下降。 2. Low blood glucose level will stimulate pancreas to secrete more glucagon and fewer insulin.低 血糖水平會刺激胰臟會分泌較多高血糖素，但較少胰島素。 3. Glucagon will stimulate liver cells to convert stored glycogen into glucose. It will increase the blood glucose level in hepatic vein to a level higher than normal.高血糖素會刺激肝細胞將已 貯存的糖原轉化成葡萄糖。這會令肝靜脈的血糖水平提升至高於正常水平。 4. The whole process will increase the blood glucose level back to normal.過程最終將身體血糖 提升至正常水平。  Storage of glycogen, iron and lipid-soluble vitamins.儲存糖原、鐵和脂溶性維生素。  Secretes bile (in this aspect, liver can be regarded as a digestive glands)製造膽汁。（因此肝臟可被 視為消化腺體）  Convert carotene into vitamin A.把胡蘿蔔素轉化成維生素 A。  Excess amino acids are broken down by deamination. The removed amino groups will be converted to urea which will be excreted in urine. The other parts of the amino acid will be converted to carbohydrate or lipid.經脫氨作用，分解過多的氨基酸。氨基酸的氨基被移除，形成尿素，經尿 排出體外；氨基酸的其餘部分則變成碳水化合物或脂質。  Detoxification: It changes mild toxins (e.g. alcohol and medicine) into harmless substances.解毒：將 溫和的毒素（如酒精和藥物）轉化為無害物質。 Other important functions of liver：肝還有其他重要功能：  Produce heat and helps in thermoregulation.產生熱，以助體溫調節。  Breakdown aged red blood cells and haemoglobin. The iron produced will be stored up, and the other remaining parts will become bile pigment and pass out of the body along with faeces.分解衰老 的紅血球及血紅蛋白。分解出來的鐵質會被儲起來，而其餘部分則生成膽色素，隨糞便排出體 外。 6.8 Egestion 排遺  The food substance left behind after digestion and absorption is called faeces. They consist of indigestible food such as dietary fibre, secretions from the alimentary canal, bacteria, dead cells from the intestinal wall and a small amount of water.食物被消化及吸收後，剩下的物質稱為糞便。糞便 由一些不能消化的食物如食用纖維、消化道的分泌物、細菌、脫落的腸壁細胞和小量水份組成。  Faeces are temporarily stored in the rectum which will be expelled from the body through the anus later.糞便會暫時儲存在直腸中，稍後經肛門排出體外。  The process of expelling faeces from the body is called egestion. (egestion is not excretion. In fact, egestion also involves the removal of metabolic wastes e.g. bile pigment)把糞便排出體外的過程稱 為排遺（大便）。（排遺並非排泄！實際上排遺過程亦涉及排泄，因糞便含有代謝廢物：膽色 素）  When the alimentary canal get stimulated during an infection, peristalsis will become too fast that too little water will be absorbed and results in diarrhea.當腸道因感染而受刺激時，過速的蠕動令 太少的水份被吸收，會引致肚瀉。  If the diet lack dietary fibre, peristalsis will become too slow that too much water will be absorbed, making the faeces very hard and results in constipation.若缺乏食用纖維，過慢的蠕動反而會令過 多的水分被吸收，糞便變硬，引致便秘。 6-19 2018 年 9 月 7 日 編 者： 葉榮昌 先生 僅供 本校 學生使 用， 不得轉 售或 作商業 用途