5 Вариант

«DIGESTION»

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Very little natural food can serve as nourishment just as it is, glucose is about the only natural substance that can. While chemists were trying to find what foods are made of, physiologists were trying to learn just what food must be used as nourishment.

It soon became evident to the physiologists that foodstuffs must undergo enormous changes in the human body, because the body tissues are profoundly different from the foodstuffs that nourish them. There is very little carbohydrate in the animal body and human fat is not much like either the vegetable fats or milk fat. Certainly the hair, skin and muscles bear little resemblance to the proteins of eggs, milk or wheat.

The word “food” is used loosely to designate anything edible whether it is a natural product such as wheat, fish, or potatoes, a partially processed product such as flour; or cooked foods such as an apple-pie. If it is edible it is food regardless of what must be done to it before it is eaten. Because of this uncertainty of meaning, the nutritionists use the word “food-stuffs” for those portions of the foods the body can use, mainly the carbohydrates, fats and proteins.

All digestion is a reaction of the foodstuffs with water or what the chemist calls a hydrolysis. As the digested food passes along the intestines it consists of 3 sugars, mostly glucose, about 20 amino acids, glycerol and several fatty acids. There are also salts and some other substances that were in the food, such as acids, chlorophyll, cholesterol and vitamins. Such is the food as it passes through the intenstinal wall into the blood stream to be distributed to the various tissues for growth, repair, or the production of energy.

6 Вариант

«MINERALS AND HUMAN BODY»

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There are 88 chemical elements in the crust of the earth. All the plant and animal life is composed of some of these elements.

Many chemists have contributed to our knowledge of the roles of the various mineral elements in nutrition.

Calcium is the most abundant mineral in the body. The average man contains over 2.5 lb* of it of which 93% is in the bones and teeth. There is only 1 part of calcium in 10,000 parts of blood, but it serves several purposes; it controls the texture of the cell membranes, affects the heartbeat and the nerve and muscle action, and regulates the activity of several enzymes.

The bones and teeth contain about half as much phosphorus as calcium, but the soft tissues contain more phosphorus than calcium.

Phosphorus, like calcium, is not simply a structural element of the body but it takes part in metabolism. Phosphorus combines with the fats and the proteins to form compounds that are essential components of the heart, brain, and other vital organs.

There is less than 3 gm of iron in the adult human body. It is a part of several tissues, although most of it is in the blood and nearly all of it is combined with protein. The iron in blood is part of the protein, hemoglobin, which makes up the greater portion of the red corpuscles. It is the iron in this protein that carries oxygen to all the tissues of the body; each molecule of hemoglobin can carry four molecules of oxygen. If there is not enough iron supplied in the blood, anemia results.

* libra = pound – фунт (423г)