4. Информативное чтение: 30 мин

6.1 Vitamins

Vitamins are organic chemical substances, widely distributed in natural foodstuffs, that are essential to normal metabolic functioning of human beings and lower animals. Only very small amounts are needed, but lack of the necessary amount, however small, results in a vitamin-deficiency disease (avitaminosis). Among the classical examples of such diseases are rickets, scurvy, beriberi, and pellagra.

The word vitamin was invented in 1911 by a Polish chemist, Casimir Funk, who was trying to ex­tract from rice hulls a chemical substance that would cure beri-­ beri. He thought he had found an amine chemical vital to life. He hadn't, but his theory was correct: lack of certain chemical substances caused disease.

The chemical structure of many vitamins is known. They are used to enrich foods, notably flour, from which natural vitamins are re­moved in the manufacture. Vitamins in the body enter into the complicated enzyme reactions by which food is digested, absorbed, and assimilated. When different vitamins were first discovered, it was common practice to name them by letters of the alphabet. So many have now been found that it is more practical to give them chemical names. Thus vitamin B1 is now called thiamine; vitamin C - ascorbic acid.

Vitamins are distinguished as fat-soluble — notably vitamins A, D and К — and water-soluble — most of the others. Some are heat-labile, destroyed by cooking, notably vitamin C; most are heat-stable.

Are vitamin pills necessary? Generally, no. A good mixed diet of common foods supplies a human being with all the vitamins he needs. Adding vitamin pills or concentrates to a good mixed diet will not increase resistance to disease. Multiple vitamins plus minerals in inexpensive tablets or capsules, taken once a day, represent a convenient way to fortify one's diet. Fortunately, moderate overdoses of vitamins do no harm. Vitamin supplements are sometimes clearly necessary. They are needed whenever the dietary intake of vitamins is inadequate. This condition frequently occurs in the presence of severe illnesses, after surgical operations, on low-calorie reducing diets, and during pregnancy. Vitamin needs differ with age. Thus vitamin D is much more essential to infants and growing children than to adults.

Vitamins in the diet: Practically speaking, only a few of the many vitamins have to be seriously considered in formulating diets. These important vitamins are A, C, D, and the vitamin В complex.

5. Письменный перевод со словарем. 30 мин

The liver

The liver, weighing about 1.5 kg, makes up 3-5% of the body weight. It originated as a digestive organ but its functions are now much more diverse.

In an adult human, the liver is typically 28 cm × 16 cm × 9 cm although its exact size varies considerably according to the quantity of blood stored within it. It is found immediately below the diaphragm, to which it is attached. Blood is supplied to the liver by two vessels: the hepatic artery, which carries 30% of the liver's total blood supply, brings oxygenated blood from the aorta; the hepatic portal vein supplies 70% of the liver's blood and is rich in soluble digested food from the intestines. A single vessel, the hepatic vein, drains blood from the liver. In addition, the bile duct carries bile produced in the liver to the duodenum.

The branches of the hepatic artery and those of the hepatic portal vein combine within the liver to form common venules which lead into a series of channels called sinusoids. These are lined with liver cells or hepatocytes. Between the hepatocytes are fine tubes called canaliculi in which bile is secreted. The canaliculi combine to form bile ducts which drain into the gall bladder where the bile is stored before being periodically released into the duodenum.