跟读练习: Human digestive system - How it works! (Animation) - 通过YouTube学习英语口语
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The human digestive system is very complex and has evolved over millions of years.
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The human digestive system is very complex and has evolved over millions of years.
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It basically consists of the rectum,
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the large intestine, the small intestine,
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the pancreas, the stomach, also called gaster and ventriculus,
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and the liver with the gallbladder.
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The esophagus is also part of this system as well as various salivary glands near the mouth.
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First, the food is broken up in the mouth by the teeth
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and then mixed with saliva with the help of the salivary glands.
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Saliva contains a digestive enzyme called amylase that already begins to digest carbohydrates in the mouth.
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It splits carbohydrates into smaller units.
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The ball-like mixture of food with saliva,
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also known as bolus, is pushed into the throat by the tongue,
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and finally into the esophagus,
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which propels the bolus to the stomach.
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The esophageal lumen, that is,
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the opening inside the esophagus,
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is very flexible, which allows boluses of different sizes to be transported.
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The esophagus consists of several layers.
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These layers occur throughout the entire digestive tract.
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The two outer muscle layers are responsible for peristalsis.
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Through these two muscles, the bolus can be transported from the mouth to the stomach,
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even if the person is standing on his head.
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The stomach is often divided into six areas.
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The stomach is composed of a similar structure to the esophagus.
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It has a longitudinal muscle layer on the outside.
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Underneath, we can find circular muscle fibers.
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In addition to this, there is an oblique muscle layer overlaying the mucosa.
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On the inside, there are rugae that allow the stomach to enlarge when food is consumed.
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The stomach wall contains gastric glands.
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They produce mucus, which is able to protect the stomach wall from the secreted gastric acid.
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Gastric acid is produced by simply smelling or seeing food,
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but also spices, and the stretching of the stomach causes the secretion,
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that is, the release of gastric acid.
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About 1-2 liters of gastric juice are produced per day.
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Since the esophagus does not have a protective mucus layer like the stomach,
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stomach and esophagus are separated by a sphincter.
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It relaxes when a bolus is pushed from the esophagus into the stomach
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and then contracts to prevent acid and food from going back up.
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Gastric juice consists, among other things,
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of hydrochloric acid, the enzyme pepsin,
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the intrinsic factor, and lipase for the digestion of fat.
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In addition to nutrients, food also contains bacteria that can damage the body.
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The components of hydrochloric acid are able to destroy harmful bacteria.
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In addition, hydrochloric acid converts pepsinogen,
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also released by the gastric glands, into pepsin.
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is able to break down proteins in the stomach.
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For a vitamin B12 absorption in the small intestine,
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the intrinsic factor is needed,
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which is produced by the gastric glands.
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The vitamin must combine with intrinsic factor,
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then it can be absorbed later by the small intestine.
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Vitamin B12 helps keep the body's nerve and blood cells healthy and helps make DNA.
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It also contains gastric lipase,
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an acid-resistant enzyme for fat digestion.
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In the stomach, gastric lipase splits a triglyceride into a free fatty acid and a diglyceride,
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whereby only the free fatty acid can be absorbed by the body.
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More effective fat digestion takes place in the small intestine.
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Through gastric juice and stomach movements,
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which take place approximately every 20 seconds,
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the individual boluses are mixed to a semi-fluid mass of partly digested food, the so-called chime.
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The chime cannot enter the duodenum at first because there is a sphincter at the stomach exit.
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The pyloric sphincter resembles the esophageal sphincter.
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The pyloric sphincter opens only a few millimeters,
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so that larger pieces remain inside the stomach.
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In the first section of the small intestine,
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the duodenum, bile, and pancreatic secretions are mixed with the chyme via the ampulla of vader.
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Pancreatic juice contains numerous digestive proenzymes and enzymes.
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In order for these to do their job,
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a higher pH value than that in the stomach is necessary.
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For this reason, pancreatic juice contains sodium hydrogen carbonate.
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Hydrogen carbonate is able to neutralize the acid in the chyme and thus produce the optimum pH value of 7 or 8.
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Pancreatic juice also contains proenzymes.
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It is only through enterokinase,
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released by the duodenum wall,
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that the proenzyme trypsinogen becomes trypsin,
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which can split proteins and activate other trypsinogens.
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We also find alpha amylase,
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which we had already found in the mouth.
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It now does the rest regarding the splitting of carbohydrates,
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which it converts into maltose and isomaltose.
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Furthermore, pancreatic lipase is able to split triglycerides into two free fatty acids.
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The gastric lipase, as we have seen before,
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can produce only one free fatty acid.
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The pancreatic lipase can cleave triglycerides excellently because the bile breaks the fats down into tiny droplets.
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This is called emulsification.
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Numerous other enzymes are part of pancreatic juice,
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but these will not be explained in detail here.
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Bile is produced by the liver cells and transported to the gallbladder.
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The bile is stored in the gallbladder and finally added to the food in the duodenum via the ampulla of VATR.
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The pancreas also releases juice via the ampulla of VATR.
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The small intestine consists of three sections, duodenum, jejunum, and ileum.
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The ileum continues into the large intestine in the right lower abdomen.
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The duodenum and the jejunum have circular folds to increase the contact surface with the food.
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These circular folds extend about 1 cm into the lumen of the small intestine.
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These folds are covered with small finger-like projections called villi.
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Villi increase the surface considerably.
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Villi are about 1 mm long.
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Each villus contains blood capillaries and a lymphatic capillary called lacteal,
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which we will see later.
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The nutrients, marked green here,
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are absorbed by the villus and transferred to the blood capillaries.
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Some nutrients, such as glucose,
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do not require a carrier.
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They are transported freely in the bloodstream.
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Other nutrients, such as iron,
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require transport proteins like transferrin.
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Fats are transported by chylomicrons, which are lipoproteins.
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The triglycerides to be transported are virtually enclosed in the lipoprotein.
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Chylomicrons and triglycerides are then transported through the lacteal of the villus.
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Each villus is covered by even smaller microvilli.
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They multiply the intestinal surface considerably.
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The microvilli absorb nutrients and transport them to the inside.
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The last part of the small intestine is the ileum.
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It does not have, unlike the duodenum and jejunum, circular folds.
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The ileum absorbs electrolytes such as calcium for building bones, hair and teeth.
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Trace elements such as zinc for sperm production and the immune system.
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such as B12 for the formation and maturation of red blood cells
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and remaining bile acid which is transported back to the liver via the bloodstream
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as with the esophagus the food is transported by peristalsis in contrast segmentation contractions serve to mix the chime,
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which is shown here in yellow and red to make it easier to see the mixing process.
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The large intestine is thicker than the small intestine.
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It is about one meter long and surrounds the small intestine.
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The small intestine is connected to the large intestine via the Bauheims valve.
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It opens when Chime is to pass from the small intestine to the large intestine.
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The large intestine does not have any villi like the small intestine
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because most digestible substances have already been absorbed in the small intestine.
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However, the large intestine has an estimated 100 billion bacteria inside.
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They are important for many other tasks,
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such as the production of vitamins and the decomposition of fiber for the body's energy production.
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Many of these bacteria are an important part of the immune system by killing harmful germs.
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Through peristalsis, the chime is transported from the ascending colon to the transverse colon to the descending colon.
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On its way through the large intestine,
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water is removed from the chyme.
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Furthermore, mucus is added for proper excretion of waste.
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Substances that cannot be absorbed through the small intestine or the large intestine remain in the rectum
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and are finally excreted through the anus.
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本课简介
在本课中，学习者将通过观看此关于人类消化系统的视频，了解其复杂的工作机制。通过这个过程，您将能够提升您在英语口语中的流利度和清晰度，特别是在讨论与健康相关的话题时。此外，此视频为您提供了丰富的专业词汇，使您能够更自信地表达有关生物学和医学的主题。通过反复练习，您将提高英语发音，增强您的雅思口语练习能力。
关键词汇与短语
- 消化系统 (digestive system)
- 食道 (esophagus)
- 胃 (stomach)
- 胰腺 (pancreas)
- 胆囊 (gallbladder)
- 胃酸 (gastric acid)
- 营养物质 (nutrients)
- 维生素B12 (vitamin B12)
练习技巧
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