ЛЕКЦИЯ № 40. Sources of energy

The fuels of the body are carbohydrates, fats and proteins. These are taken in the diet.

Carbohydrates are the principal source of energy in most diets. They are absorbed into the blood stream in the form of glu cose. Glucose not needed for immediate use is converted into glycogen and stored in the liver. When the blood sugar concentra tion goes down, the liver reconverts some of its stored glycogen into glucose.

Pats make up the second largest source of energy in most diets. They are stored in adipose tissue and round the principal internal organs. If excess carbohydrate is taken in, this can be converted into fat and stored. The stored fat is utilized when the liver is empty of glycogen.

Proteins are essential for the growth and rebuilding of tissue, but they can also be utilized as a source of energy. In some diets, such as the diet of the Eskimo, they form the main source of energy. Proteins are first broken down into amino acids. Then they are absorbed into the blood and pass round the body. Amino acids not used by the body are eventually excreted in the urine in the form of urea. Proteins, unlike-carbohydrates and fats, cannot be stored for future use.

The digestive system, or gastrointestinal tract, begins with the mouth, where food enters the body, and ends with the anus, where solid waste material leaves the body. The primary function of the organs of the digestive system are threefold.

First, complex food material which is taken into the mouth must be digested mechanically and chemically, as it travels through, the gastrointestinal tract.

Second, the digested food must be absorbed by passage through the walls of the small intestine into the blood stream so that the valuable energy-carrying nutrients can travel to all cells of the body.

The third function of the gastrointestinal tract is to eliminate the solid waste materials which are unable to be absorbed by the small intestine.

In the man the food in the mouth is masticated, that is to say it is bitten and broken up by the teeth and rolled into the bolus by the tongue.

The degree of chewing which is possible depends on the jaw articulation, the latter depending on the food. Mastication is voluntary, but it may be reflex, each closure of the jaw acting as a stimulus for their reopening.

After mastication the bolus is swallowed: the swallowing starts as a voluntary movement, but its accomplishment is a chain of reflexes involving the movement of the food by peristalsis, the closure of the nasal and tracheal openings, and the cessation of respiration. Cranial nerves V, IX, and XII are involved.

Peristalsis is a type of muscular contraction characteristic of the gut and consists in waves of contraction, these running along the muscles, both circular and longitudinal, towards the anus.

If the food is fluid it enters the stomach six seconds after the beginning of the act, but If It is solid it takes much long er, up to fifteen minutes, to pass down the esophagus.

In the stomach the food is thoroughly mixed by the series of contractions, three or four a minute, the contraction waves pass ing from the middle of the stomach to the pylorus. These tend to drive the food in the same direction, but the pylorus being closed, there is axial reflex, owing to which the food is well mixed. After a time – a bout a minute when water has been swallowed – the pylorus relaxes at each wave, allowing some of the stomach contents to enter the duodenum. Fat stays in the stomach longer than carbo hydrate, but all food leaves generally in three or four hours. In the small intestine the food continues to be moved by peristalsis, the latter controlled by the deep nerve plexus. The small intestine undergoes segmentation movements, the food contents being thoroughly mired The wall becomes constricted into a number of segments and then about five seconds later the constrictions disappear, there being another set exactly out of phase with the first. The large intestine undergoes infrequent powerful contractions, food having entered it. From the large intestine the food enters the rectum.

New words

fuels – топливо

carbohydrates – углеводы

fats – жиры

proteins – белки

diet – диета

principal source – основной источник

energy – энергия

glucose – глюкоза

immediate – непосредственный

use – использование

is converted – преобразован

glycogen – гликоген

stored – сохраненный

liver – печень

sugar – сахар

adipose – животный жир

excess – избыток

utilized – используемый

empty – пустой

essential – основа

growth – рост

rebuilding – восстановление

acids – кислоты

amino acids – аминокислоты

contractions – сокращения

pylorus – пилорус

direction – направление

axial reflex – осевое отражение

Past Continuous Tense (Past Progressive Tense) (действие в процессе, совершалось в определенный момент или протекало в течение четко ограниченного периода времени в прошлом).

Спряжение глагола to work в Past Continuous Tense Таблица 12

Раскройте скобки, употребляя глголы в Present Continuous или Past Continuous.

1. I (to write) an English exercise now.

2. I (to write) an English exercise at this time yesterday.

3. My little sister (to sleep) now.

4 My little sister (to sleep) at this time yesterday.

5. My friends (not to do) their homework now. They (to play) volley-ball.

6. My friends (not to do) their homework at seven o'clock yesterday. They (to play) volley-ball.

7. You (to eat) ice-cream now?

8. You (to eat) ice-cream when I rang you up yesterday?

9. What your father (to do) now?

10. What your father (to do) from eight till nine yesterday?

11. Why she (to cry) now?

12. Why she (to cry) when I saw her yesterday?

13. She (to read) the whole evening yesterday.

14. She (not to read) now.

15. Now she (to go) to school.

16. What you (to do) now? – I (to drink) tea.

17. You (to drink) tea at this time yesterday? – No, I (not to drink) tea at this time yesterday, I (to eat) a banana.

18. My sister is fond of reading. She (to read) the whole-evening yesterday, and now she (to read) again.

19. Look! My cat (to play) with a ball.

20. When I went out into the garden, the sun (to shine) and birds (to sing) in the trees.

Answer the questions.

1. What are the fuels of the body?

2. What is the principal source of energy in most diets?

3. Where are the carbohydrates absorbed?

4. What is converted into glycogen and stored in the liver?

5. What makes up the second largest source of energy in most diets?

6. Where pats are stored?

7. When is the stored fat utilized?

8. What are proteins essential for?

9. In what are proteins first broken down?

10. What is going on with the food in the stomach?

Make the sentences of your own using the new words (10 sentences). Find the verb to be in the text. Explain why it is used in such a way?