2015-05-26
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1. The present text is given to explain the processes of digestion and absorption. The more we know about them, the better we shall under-stand how important these processes are.
2. Every cell of the human body requires certain chemical nutrients in the fluids that surround it. In order to supply these nutrients, the body must break down complex foods into molecules small enough to pass through tissues, enter the blood stream or lymphatic systems, and be delivered in a soluble? form to the various body cells. This break of insoluble forms is known as digestion; the passage of such'substances into the blood stream or lymph is known as absorption.
3. The human digestive tract is a long, muscular tube (up to 25 feet in length) that begins at the mouth and ends at the anus. This tube consists of the oral cavity, pharynx, esophagus, small intestine, and large intestine.
4. Several glands, located outside the digestive tract, are also impor* tant in the digestive process. Our tast is to describe them in detail.
These glands, known as accessory glands, are connected by ducts td the digestive tube. These accesory glands include the salivary glands,'
Lesson 9 ♦ 121
Food qnters the
___ ±___
Oral cavity
4 с, •
Pharinx
I
Esophagus
Liver
+ Bile
Stomach
Gall-bladder
Pancreas
Bile
Small intestine
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Pancreatic juice
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Large intestine
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Anus Feces leave the body
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Fig. 9. Pathway of food through the digestive tract.
liver, gall-bladder and the pancreas. Each gland produces secretions
i hat function in the digestive process, and each is therefore part of the
digestive system.,_/ V с / ■ о', л ■ i
5. The process of digestion is due to the activity of many enzymes, i hemicals, and physical processes within the digestive tract. According to I he area in which digestion is carried on, these digestive processes may be classified as salivary digestion, when occurring in the mouth; gastric digestion in the stomach; and intestinal digestion in the small intestine. In I he large intestine (the last section of the digestive tube) no digestion lnkes place. Here water is absorbed, bacteria grow, and the unabsorbed solid-residue wastes of digestion collect and are excreted as feces.
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6. The absorption means the passage of digested foods through the lining of the intestines into the blood or lymph. Practically all absorption takes place in the small intestine. A few drugs and alcohol are •ihsorbed through the walls of the stomach, but no foods. Glucose is an exception, but it must be present in such high concentrations as to muse vomiting. Furthermore, we eat very little glucose, which is formed mainly in the small intestine due to the action of the dissaccharide-
122 ♦ Learning to Understand a Medical Text
splitting enzymes. Therefore, absorption of food does not normally occur through the stomach walls.
7. Water is absorbed throughout the length of the small intestine and also, as has been noted, in the ascending limb of the colon. With normal digestion, between 95 and 100 per cent of all carbohydrates, fats, and animal proteins are absorbed. Plant proteins, such as beans or peas, are protected by the plant cell membrane, so that only 60 to 70 per cent are absorbed. The remaining 30 to 40 per cent undergo bacterial decomposition in the intestine, which results in the formation of large amounts of intestinal gas («flatus»).
To study the pathway of food through digestive tract is very important for explanation of the process of digestion.
Упражнение 8. 1) Прочтите и переведите текст А. Второй абзац переведите письменно. 2) Найдите в тексте ответы на следующие вопросы и прочтите их.
1. How are nutrients supplied to the body? 2. What processes are known as digestion and absorption? 3. What do we call the parts of the digestive tube from the mouth up to the anus? 4. Is glucose absorbed from the stomach or the small intestine? 5. Water and drugs arc absorbed through the stomach walls, aren't they?
3) Найдите в каждом абзаце предложения, выражающие основную мысль первого абзаца.
4) Составьте письменно план текста А.
Упражнение 9. Найдите в каждом ряду слово, противоположное по значению первому слову ряда.
1. soluble - decomposed, dissoluble, diluted, insoluble; 2. to include -to conclude, to exclude, to leave out; 3. solid — hard, weak, soft, firm, soluble; 4. ascending - going up (down), descending, sitting down
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Упражнение 10. Переведите следующие предложения, определите функции инфинитива.
1. The present investigation is carried out to determine the liver functions in experimental dogs. 2. An attempt was made to correlate metabolism with humidity, light, or average daily temperature. 3. One of the purposes of this work is to prevent the action of the dissaccharide-split-ting enzymes. 4. In order to ensure more adequate oxygenation the fluids bathing the mucose were recirculated. 5. From the curves of the blood ammonia concentration it is possible to obtain necessary information.
Lesson 9 <> 123
