17.3 消化和吸收
Section outline
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Competitive Eating
::竞争性饮食This man is on his way to coming in third in an international hot dog eating contest. It may look as though he is regurgitating his hot dogs, but in fact, he is trying to get them into his mouth and down his throat as quickly as he can. In order to eat as many hot dogs as possible in the allotted time, he pushes several into his mouth at once, and doesn’t bother doing much chewing. Chewing is normally the first step in the process of digestion .
::这名男子正准备在一次国际热狗饮食比赛中排行第三。 这名男子可能看起来像是在反动热狗,但事实上,他正试图尽快把热狗塞进嘴里,从喉咙中咽下去。 为了在分配的时间里尽可能多地吃热狗,他一次把几个热狗推进嘴里,不费吹灰之力。 骗子通常是消化过程的第一步。Digestion
::文摘Digestion of food is a form of catabolism, in which the food is broken down into small molecules that the body can absorb and use for energy , growth, and repair. Digestion occurs when food is moved through the . It begins in the mouth and ends in the . The final products of digestion are absorbed from the digestive tract, primarily in the small intestine. There are two different types of digestion that occur in the digestive system: mechanical digestion and chemical digestion . The diagram summarizes the roles played by different digestive organs in mechanical and chemical digestion, both of which are described in detail below.
::食物的消化是一种代谢形式,在这种形式中,食物被分解成小分子,身体可以吸收和使用这些分子,用于能源、生长和修理;当食物通过时,消化就会发生;从口中开始,最后的消化产物从消化道吸收,主要在小肠中;消化系统有两种不同的消化方式:机械消化和化学消化;图表概述了不同消化器官在机械和化学消化中所起的作用,下文将详细叙述这两方面。Mechanical Digestion
::机械消化Mechanical digestion is a physical process in which food is broken into smaller pieces without becoming changed chemically. It begins with your first bite of food (see photo ) and continues as you chew food with your teeth into smaller pieces. The process of mechanical digestion continues in the stomach . This muscular organ churns and mixes the food it contains, an action that breaks any solid food into still smaller pieces.
::机械消化是一种物理过程,在这种过程中,食物被分解成小块,而不会发生化学变化。它始于你第一次吃食物(见照片),接着是用牙齿把食物嚼成小块。机械消化过程持续到胃部。这种肌肉器官的发炎和混合食物,将任何固体食物分解成小块。The teeth play an important role in the mechanical digestion of food, starting with the first bite.
::牙齿在食品机械消化中起着重要作用,从第一次咬起。Although some mechanical digestion also occurs in the small intestine, it is mostly completed by the time food leaves the stomach. At that stage, food in the GI tract has been changed to the thick semi-fluid called chyme. Mechanical digestion is necessary so that chemical digestion can be effective. Mechanical digestion tremendously increases the surface area of food particles so they can be acted upon more effectively by digestive .
::虽然小肠中也存在一些机械消化,但大部分在食物离开胃时完成,在这一阶段,GI草地的食物已经改造成厚厚的半流状,称为chyme。 机械消化是必要的,这样化学消化才能有效。 机械消化会大大增加食物颗粒的表面面积,以便更有效地通过消化作用。Chemical Digestion
::化学消化Chemical digestion is the biochemical process in which macromolecules in food are changed into smaller molecules that can be absorbed into body fluids and transported to throughout the body. Substances in food that must be chemically digested include , , , and . Carbohydrates must be broken down into simple sugars , proteins into amino acids , lipids into fatty acids and glycerol, and nucleic acids into nitrogen bases and sugars. Some chemical digestion takes place in the mouth and stomach, but most of it occurs in the first part of the small intestine (duodenum).
::化学消化是一种生物化学过程,在这种过程中,食物中的大型分子变成小分子,可以吸收到体液中,并运到整个身体。必须化学消化的食品中的物质包括:、、和.碳水化合物必须分解成简单的糖、蛋白质、氨酸、脂肪酸脂和甘油,以及核酸进入氮基和糖。一些化学消化在口和胃中发生,但大部分发生在小肠道(二角)的第一部分。Digestive Enzymes
::活性酶Chemical digestion could not occur without the help of many different digestive enzymes. Enzymes are proteins that catalyze, or speed up, . Digestive enzymes are secreted by exocrine glands or by the mucosal layer of epithelium lining the gastrointestinal tract . In the mouth, digestive enzymes are secreted by salivary glands . The lining of the stomach secretes enzymes, as does the lining of the small intestine. Many more digestive enzymes are secreted by exocrine cells in the pancreas and carried by ducts to the small intestine. The following table lists several important digestive enzymes, the organs and/or glands that secrete them, and the compounds they digest. You can read more about them below.
::没有许多不同的消化酶的帮助,就不可能发生化学消化。酶是催化或加速的蛋白质。消化酶由外泌腺或胃肠道内粘附的上皮的粘合层秘而不宣。在口腔中,消化酶由唾液腺秘而不宣。胃内分泌酶的衬里和小肠内衬一样。许多更多的消化酶由胰腺内的外分泌细胞秘而不宣,并被输入小肠。下表列出了一些重要的消化酶、隐藏这些酶的器官和/或基因,以及它们消化的化合物。你可以在下面阅读更多关于这些酶的信息。Digestive Enzymes Digestive Enzyme
::消化酶Organ, Glands That Secretes It
::机关、秘密地Compound It Digests
::复类文摘Amylase
::艾米拉Salivary Glands, Pancreas
::盐盐地、潘克里亚斯Amylose (Polysaccharide)
::艾米洛特( 极焦炭)Sucrase
::统治Small Intestine
::小不小Sucrose (Disaccharide)
::Sucrosse( 荒漠化)Lactase
::晶晶体Small Intestine
::小不小Lactose (Disaccharide)
::Lactose( 荒漠化)Lipase
::LipaseSalivary Glands, Pancreas
::盐盐地、潘克里亚斯Lipid
::利皮Pepsin
::Pepspepsin 比索Stomach
::胃Protein
::蛋白素Trypsin
::试试Pancreas
::胰腺Protein
::蛋白素Chymotrypsin
::间歇性催化素Pancreas
::胰腺Protein
::蛋白素Deoxyribonuclease
::脱氧离Pancreas
::胰腺Ribonuclease
::里博核释放Pancreas
::胰腺Nuclease
::启用Small Intestine
::小不小Small Nucleic Acids
::小型核酸Chemical Digestion of Carbohydrates
::碳水合物化学消化About 80 percent of digestible carbohydrates in a typical Western diet are in the form of the plant polysaccharide amylose, which consists mainly of long chains of glucose and is one of two major components of starch . Additional dietary carbohydrates include the polysaccharide glycogen, along with some sugars, which are mainly disaccharides .
::在典型的西方饮食中,大约80%的可消化碳水化合物以植物聚沙酸亚米洛植物的形式出现,主要由长链的葡萄糖组成,是淀粉的两个主要成分之一。 额外的饮食碳水化合物包括聚沙酸酯甘油,以及一些糖,这些糖主要是脱焦剂。The process of chemical digestion for some carbohydrates is illustrated the figure . To chemically digest amylose and glycogen, the enzyme amylase is required. The chemical digestion of these polysaccharides begins in the mouth, aided by amylase in saliva . Saliva also contains mucus — which lubricates the food — and hydrogen carbonate, which provides the ideal alkaline conditions for amylase to work. Carbohydrate digestion is completed in the small intestine, with the help of amylase secreted by the pancreas. In the digestive process, polysaccharides are reduced in length by the breaking of bonds between glucose monomers . The macromolecules are broken down to shorter polysaccharides and disaccharides, resulting in progressively shorter chains of glucose. The end result is molecules of the simple sugars glucose and maltose (which consists of two glucose molecules), both of which can be absorbed by the small intestine.
::图表说明了某些碳水化合物的化学消化过程。为了化学消化藻类和甘油,需要酶氨基酶。这些聚沙酸盐的化学消化始于口中,由盐碱中的氨酸酶协助。盐碱还含有黏液——它使食物润滑——和碳酸氢,它为氨酸盐发挥作用提供了理想的碱条件。碳水化合物消化过程在小肠中完成,由胰腺分解的氨基酶帮助。在消化过程中,由于葡萄糖单体之间的粘合破裂,聚沙酸酯的消化长度缩短了。巨藻素分解成较短的聚沙酸盐和脱硫酸,导致葡萄糖链逐渐缩短。最终结果是简单的糖甘蔗和麦芽(由两种甘糖分子组成)的分子在小肠中,这两种分子都可以被小肠吸收。Other sugars are digested with the help of different enzymes produced by the small intestine. S ucrose (or table sugar), for example, is a disaccharide that is broken down by the enzyme sucrase to form glucose and fructose, which are readily absorbed by the small intestine. Digestion of the sugar lactose, which is found in milk, requires the enzyme lactase, which breaks down lactose into glucose and galactose. Glucose and galactose are then absorbed by the small intestine. Fewer than half of all adults produce sufficient lactase to be able to digest lactose. Those who cannot are said to be lactose intolerant.
::其他的糖在小肠生产的不同酶的帮助下被消化。例如,苏克罗斯(或餐桌糖)是一种分解的分解物,由小肠中容易吸收的酶苏卡塞分解成葡萄糖和纤维糖。在牛奶中发现的糖乳糖的消化需要酶乳酶,它将乳糖分解成葡萄糖和甘糖。然后,小肠吸收了甘蔗和甘蔗。不到一半的成年人生产足够的乳糖,能够消化乳糖。据说,那些不能消化乳糖的人不耐乳糖。The process of chemical digestion for some carbohydrates
::一些碳水化合物的化学消化过程Chemical Digestion of Proteins
::蛋白质化学消化Proteins consist of polypeptides , which must be broken down into their constituent amino acids before they can be absorbed. An overview of this process is shown in the figure . Protein digestion occurs in the stomach and small intestine through the action of three primary enzymes: pepsin (secreted by the stomach), and trypsin and chymotrypsin (secreted by the pancreas). The stomach also secretes hydrochloric acid, making the contents highly acidic, which is a required condition for pepsin to work. Trypsin and chymotrypsin in the small intestine require an alkaline environment to work. Bile from the liver and bicarbonate from the pancreas neutralize the acidic chyme as it empties into the small intestine. After pepsin, trypsin, and chymotrypsin break down proteins into peptides, these are further broken down into amino acids by other enzymes called peptidases, also secreted by the pancreas.
::蛋白质在吸收之前必须分解成其成分的氨基酸。图中显示了这一过程的概况。胃和小肠中的蛋白质消化通过三种主要酶作用在胃和小肠中发生:Pepsin(由胃分泌),Trepsin和chmotropsin(由胰腺分泌)。胃分泌盐酸,使含量高酸,这是pepsin工作的一个必要条件。小肠中的Trepsin和chmotropsin需要有一个碱性环境来工作。从肝脏和双碳酸性细胞中中消酸性,因为它将酸性神经排入小肠。在pepsin、trepsin和hymotropsin分解蛋白分解成peptide,这些物质又被称为peptidas的其他酶进一步分解成氨基酸,这些酶也是由胰岛秘密的。Chemical digestion of proteins. Only the enzyme pepsin is shown, but other enzymes are involved in this process.
::蛋白质的化学消化,只显示酶epsin,但其他酶也参与了这一过程。Chemical Digestion of Lipids
::利皮化学消化The chemical digestion of lipids begins in the mouth. The salivary glands secrete the digestive enzyme lipase, which breaks down short-chain lipids into molecules consisting of two fatty acids. A tiny amount of lipid digestion may take place in the stomach, but most lipid digestion occurs in the small intestine.
::脂肪的化学消化始于口腔。唾液腺分泌了消化酶脂,将短链脂分解成由两颗脂肪酸组成的分子。 少量脂肪消化可能在胃中发生,但大部分脂肪消化发生在小肠中。Digestion of lipids in the small intestine occurs with the help of another lipase enzyme from the pancreas, as well as bile secreted by the liver. As shown in the diagram , bile is required for the digestion of lipids, because lipids are oily and do not dissolve in the watery chyme. Bile emulsifies (or breaks up) large globules of food lipids into much smaller ones, called micelles, much as dish detergent breaks up grease. The micelles provide a great deal more surface area to be acted upon by lipase, and also point the hydrophilic (“water-loving”) heads of the fatty acids outward into the watery chyme. Lipase can then access and break down the micelles into individual fatty acid molecules.
::小肠中脂肪的消化过程是在另一颗来自胰腺的脂酶酶的帮助下发生的,还有肝脏的肉卷。如图所示,脂肪的消化需要肉卷,因为脂肪油性强,不溶于水状的旋流中。小肠将大块的食品脂凝胶溶化(或分解)成小得多的凝块,称为小鼠,就像洗涤剂粉碎油脂一样。小鼠可以提供更多的表面面积,用脂类来操作,并将脂肪酸的流体(“爱水”)头指向水状的曲流。 利帕可以进入(或分解)大块的老鼠,然后将小块分解成个别脂肪酸分子。Both bile from the liver and lipase from the pancreas help digest lipids in the small intestine.
::肝脏的胆汁和胰腺的唇膏都有助于消化小肠的脂肪。Chemical Digestion of Nucleic Acids
::核酸化学消化Nucleic acids (DNA and RNA) in foods are digested in the small intestine with the help of both pancreatic enzymes and enzymes produced by the small intestine itself. Pancreatic enzymes called ribonuclease and deoxyribonuclease break down RNA and DNA, respectively, into smaller nucleic acids. These, in turn, are further broken down into nitrogen bases and sugars by small intestine enzymes called nucleases.
::食物中的核酸(DNA和RNA)在小肠中消化,同时利用小肠本身产生的胰腺酶和酶。 被称为肋骨释放和脱氧核糖核酸的胰腺酶分别分解为小核酸和DNA,再用小肠酶(Nuclease)进一步细分为氮基和糖。Chemical Digestion by Gut Flora
::古特弗洛拉的化学消化The human gastrointestinal tract is normally inhabited by trillions of , some of which contribute to digestion. Here are just two of dozens of examples:
::人类胃肠道通常居住数万亿人口,其中一些有助于消化。-
The most common carbohydrate in plants —
cellulose
— cannot be digested by the human digestive system, but tiny amounts of cellulose are digested by bacteria in the
.
::植物中最常见的碳水化合物——纤维素——不能被人类消化系统消化,但微量的纤维素却被细菌消化。 -
Certain bacteria in the small intestine help digest lactose, which many adults cannot otherwise digest. As a byproduct of this process, the bacteria produce lactic acid, which increases the release of digestive enzymes and the
absorption
of
minerals
, such as
calcium
and iron.
::小肠中的某些细菌有助于消化乳糖,许多成年人否则无法消化乳糖。 作为这一过程的副产品,细菌产生乳酸,这增加了消化酶的释放和矿物的吸收,如钙和铁。
Control of the Digestive Process
::控制消化过程The process of digestion is controlled by both and nerves . Hormonal control is mainly by endocrine hormones secreted by cells in the lining of the stomach and small intestine. These hormones stimulate the production of digestive enzymes, bicarbonate, and bile. The hormone secretin, for example, is produced by endocrine cells lining the duodenum of the small intestine. Acidic chyme entering the duodenum from the stomach triggers the release of secretin into the bloodstream. When the secretin returns via the circulation to the digestive system, it signals the release of bicarbonate from the pancreas. The bicarbonate neutralizes the acidic chyme.
::消化过程由神经和神经控制,荷尔蒙控制主要是内分泌激素,内分泌激素由腹部和小肠内衬的细胞秘而不宣,这些荷尔蒙刺激了消化酶、双碳酸盐和胆碱的生产,例如,荷尔蒙秘诀由内分泌细胞在小肠的二角结膜内结成,从腹部进入二角结膜的酸性微粒触发秘密释放到血液中。当秘密素通过向消化系统循环回流时,它信号了双碳酸盐从胰腺中释放出来。Nerves involved in digestion include those that connect digestive organs to the , as well as nerves inside the walls of the digestive organs. Nerves connecting the digestive organs to the central nervous system cause smooth muscles in the walls of digestive organs to contract or relax as needed, depending on whether or not there is food to be digested. Nerves within digestive organs are stimulated when food enters the organs and stretches their walls. These nerves trigger the release of substances that speed up or slow down the movement of food through the GI tract and the secretion of digestive enzymes.
::消化过程中所涉及的神经元包括将消化器官与消化器官连接在一起的神经,以及消化器官墙壁内的神经元。将消化器官与中枢神经系统连接起来的神经元导致消化器官墙壁的光滑肌肉按需要收缩或放松,视消化器官壁壁上是否有需要消化的食物而定。当食物进入消化器官并伸展其墙壁时,消化器官内的神经元就会受到刺激。这些神经元触发了加快或减缓食物通过GI道流动和消化酶秘密的物质释放。Absorption
::吸收吸收When digestion is finished, it results in many simple nutrient molecules that must go through the process of absorption from the lumen of the GI tract to or lymph vessels , so they can be transported to and used by cells throughout the body. A few substances are absorbed in the stomach and large intestine. W ater is absorbed in both of these organs, and some minerals and vitamins are also absorbed in the large intestine, but about 95 percent of nutrient molecules are absorbed in the small intestine. Absorption of the majority of these molecules takes place in the second part of the small intestine, called the jejunum . T here are, however, a few exceptions — for example, iron is absorbed in the duodenum, and vitamin B12 is absorbed in the last part of the small intestine, called the ileum . After being absorbed in the small intestine, nutrient molecules are transported to other parts of the body for storage or further chemical modification. A mino acids, for instance, are transported to the liver to be used for .
::消化过程完成后,它导致许多简单的营养分子,这些分子必须从GI的润滑液吸收到淋巴容器或淋巴容器,这样它们就可以被运到整个身体的细胞中并由细胞使用。一些物质被胃和大肠吸收。一些物质被吸收在胃和大肠中;水被吸收在这两种器官中,一些矿物和维生素也被大肠吸收,但大约95%的营养分子被吸收在小肠中。吸收大部分这些分子发生在小肠的第二部分,称为Jejunum。但是,有一些例外——例如,铁被吸收在杜丘南,维生素B12被吸收在小肠的最后一个部分,称为阴道。在被吸收在小肠中,营养分子被运到身体的其他地方储存或进一步化学改变。例如,氨酸被运到肝脏,用于此目的。The epithelial tissue lining the small intestine is specialized for absorption. It has many wrinkles and is covered with villi and microvilli, creating an enormous surface area for absorption. As shown in the diagram , each villus also has a network of blood capillaries and fine lymphatic vessels called lacteals close to its surface. The thin surface layer of epithelial cells of the villi transports nutrients from the lumen of the small intestine into these capillaries and lacteals. Blood in the capillaries absorbs most of the molecules, including simple sugars, amino acids, glycerol, salts, and water-soluble vitamins (vitamin C and the many B vitamins). Lymph in the lacteals absorbs fatty acids and fat-soluble vitamins (vitamins A, D, E, and K).
::小肠内衬的上皮线组织是专门用来吸收的,它有许多皱纹,覆盖着葡萄和微小树脂,形成了一个巨大的吸收面积。如图所示,每个也有一个血液粘合剂网络和称为靠近其表面的细淋巴容器的细淋巴容器。小肠内皮的薄表层将小肠的润滑液的营养素输送到这些毛皮和花织物中。毛细的血液吸收了大部分分子,包括简单的糖、氨酸、甘油、盐类和可溶水的维他命(维生素C和许多B维他命)。乳液吸收脂肪酸和脂肪溶性维他命(维生素A、D、E和K)。This highly simplified drawing of an intestinal villus shows the capillaries and lacteals within in it that carry away absorbed substances. Note that each cell in the thin surface layer of the villus is actually covered with microvilli that greatly increase the surface area for absorption.
::肠道外壳的这一高度简化的图解显示,肠道外壳内含有吸收物质。 请注意,壳体薄表层的每个细胞实际上都覆盖在微小树脂中,这大大增加了吸收的表面积。Feature: My Human Body
::特质:我的人体The process of digestion does not always go as it should. Many people suffer from indigestion, or dyspepsia, a condition of impaired digestion. Symptoms may include upper abdominal fullness or pain, heartburn , nausea, belching, or some combination of these symptoms. The majority of cases of indigestion occur without evidence of an organic disease that is likely to explain the symptoms. Anxiety or certain foods or medications (such as aspirin) may be contributing factors in these cases. In other cases, indigestion is a symptom of an organic disease, most often gastroesophageal reflux disease (GERD) or gastritis. In a small minority of cases, indigestion is a symptom of a peptic ulcer of the stomach or duodenum, usually caused by a bacterial infection. Very rarely, indigestion is a sign of .
::消化过程并非始终如一,许多人患有消化不良或痢疾,这是消化受损的一个条件。症状可能包括上腹部完全或疼痛、心脏灼伤、恶心、结扎或这些症状的某些组合。大部分消化不良病例发生时没有能够解释症状的有机疾病的证据。在这些病例中,焦虑或某些食物或药物(如阿司匹林)可能是诱因。在其他案例中,消化不良是有机疾病的症状,最常见的是胃性复发疾病(GERD)或胃病。在少数病例中,消化不良是胃部或脑膜溃疡的症状,通常由细菌感染引起的。消化不良现象很少。An occasional bout of indigestion is usually nothing to worry about, especially in people less than 55 years of age. However, if you suffer frequent or chronic indigestion, it’s a good idea to see a doctor. If an underlying disorder such as GERD or an ulcer is causing the indigestion, this can and should be treated. If no organic disease is discovered, the doctor can recommend lifestyle changes or treatments to help prevent or soothe the symptoms of acute indigestion. Lifestyle changes might include modifications in eating habits, such as eating more slowly, eating smaller meals, or avoiding fatty foods. You also might be advised to refrain from taking certain medications, especially on an empty stomach. The use of antacids or other medications to relieve symptoms may also be recommended.
::偶尔发生消化不良通常没什么好担心的,特别是在55岁以下的人中。然而,如果你经常或长期的消化不良,那么看医生是一个好主意。如果像GERD或溃疡这样的基本疾病导致消化不良,那么可以并且应该治疗这种疾病。如果没有发现任何有机疾病,医生可以建议改变生活方式或治疗,以帮助预防或缓解急性消化不良症状。生活方式的变化可能包括改变饮食习惯,比如吃得更慢、吃得更少或避免脂肪食品。你也可以建议不要服用某些药物,特别是在空腹部。也可以建议使用蚂蚁素或其他药物来缓解症状。Summary
::摘要-
Digestion is a form of catabolism, in which food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs when food moves through the gastrointestinal (GI) tract. The digestive process is controlled by both hormones and nerves.
::消化是一种催化形式,在这种形式中,食物被分解成小分子,身体可以吸收和使用这些分子,用于能源、生长和修理;当食物通过胃肠道时,消化就会发生,消化过程由荷尔蒙和神经控制。 -
Mechanical digestion is a physical process in which food is broken into smaller pieces without becoming chemically changed. It occurs mainly in the mouth and stomach.
::机械消化是一种物理过程,在这种过程中,食物被碎成小块,而不会发生化学变化,主要发生在口腔和胃部。 -
Chemical digestion is a chemical process in which macromolecules — including carbohydrates, proteins, lipids, and nucleic acids — in food are changed into simple nutrient molecules that can be absorbed into body fluids. Carbohydrates are chemically digested to sugars, proteins to amino acids, lipids to fatty acids, and nucleic acids to individual nucleotides. Chemical digestion requires digestive enzymes. Gut flora carry out additional chemical digestion.
::化学消化是一种化学过程,在这种过程中,食物中的大型分子——包括碳水化合物、蛋白质、脂类和核酸——被改变为简单的营养分子,可以吸收到体液中,碳水化合物被化学吸收到糖、氨基酸的蛋白质、脂肪酸的脂类和各个核糖酸的核酸中,化学消化需要消化酶。 -
Absorption occurs when the simple nutrient molecules that result from digestion are absorbed into blood or lymph.
::当消化产生的简单的营养分子被血液或淋巴吸收时,即为吸收。
Review
::回顾1. Define digestion. Where does it occur?
::1. 确定消化的定义:在何处发生?2. Identify two organ systems that control the process of digestion by the digestive system.
::2. 确定控制消化系统消化过程的两个机关系统。3. What is mechanical digestion? Where does it occur?
::3. 什么是机械消化,在哪里发生?4. Describe chemical digestion.
::4. 描述化学消化。5. What is the role of enzymes in chemical digestion?
::5. 酶在化学消化过程中的作用是什么?6. What is absorption? When does it occur?
::6. 什么是吸收,何时发生?7. Where does most absorption occur in the digestive system? Why does most of the absorption occur in this organ, and not earlier in the GI tract?
::7. 消化系统吸收最多的是哪里?为什么吸收的大部分发生在这个机关,而不是更早的GI系统?8. Name two digestive enzymes found in saliva. Which type of molecule do they digest?
::8. 列出在唾液中发现的两种消化酶,它们消化的是哪种分子?9. Where is bile produced? What are some functions of bile?
::9. 哪里产生易碎物?易碎物的功能是什么?10. True or False: Pepsin digests cellulose.
::10. 真实的或假的:Pepsin消化剂是纤维素。11. True or False: Glucose can be absorbed by the body without being further broken down.
::11. 真实或假:葡萄糖可以由身体吸收,而不必进一步细分。12. The pH of the stomach ___________ .
::12. 胃部的pH值a. is neutral
::a. 是中性b. is alkaline
::b. 是碱性c. is acidic
::c. 酸性d. depends only on what you eat
::d. 只取决于你吃什么13. Lymph absorbs __________ .
::13. 淋巴结吸收a. fatty acids
::a. 脂肪酸b. sugars
::b. 糖c. amino acids
::c. 氨基酸d. vitamin C
::d. 维生素CExplore More
::探索更多Check out this video to learn more about v itamin B12 absorption and digestion:
::以了解更多维他命B12吸收和消化情况:New research shows that babies born through vaginal birth actually have a healthier gut flora . Learn more here:
::新的研究表明,通过阴道分娩出生的婴儿实际上有更健康的直肠植物。 -
The most common carbohydrate in plants —
cellulose
— cannot be digested by the human digestive system, but tiny amounts of cellulose are digested by bacteria in the
.
