ЛЕКЦИЯ № 41. The act of swallowing

The act of swallowing is divided into three stages.

The first stage is under voluntary control. The food which has been transformed into a soft, mass by the act of mastication is brought into position upon the root of the tongue, and by the action of the lingual muscles is rolled backwards towards the base of the tongue.

The second stage is brief and is occupied in guiding the food through the pharynx and past the openings that lead from it. The muscular movements during this stage are purely reflex in nature. The third stage involves the passage of the food down the eso phagus. The food is seized by peristaltic wave which, traveling along the esophagus, carries the material before it into the stomach. The cardiac sphincter which guards the lower end of the esophagus and which at other times is kept tonically closed re laxes upon the approach of the bolus which is then swept into the stomach by the wave of constriction which follows.

Shape of the stomach

The normal position of the empty human stomach is not hori zon-tal, as used to be thought before the development of rentgenology. This method of examination has revealed the stomach to be either somewhat J-shaped of comparable in outline to a reversed L. The majority of normal stomachs are J-shaped. In the J-shaped type the pylorus lies at a higher level than the lowest part of the greater curvature and the body of the stomach is nearly verti cal.

The stomach docs not empty itself by gravity, but through the contraction of its muscular wall like any other part of the diges tive tube, of which it is merely a segment.

Gastric motility shows great individual variation; in some types of stomach the wave travels very rapidly, completing its journey in from 10 to 15 seconds. In others the wave takes 30 seconds or go to pass from its origin to the pylorus. The slow waves are the more common.

IRON in the body.

It is accepted that the total amount of iron in the body is between 2 and 5 g., varying with body-weight and hemoglobin level; about two-thirds of this is in the form of hemoglobin and about 30% is storage iron; iron in myоglobin and enzymes makes up the small remaining fraction together with iron in transport, which is only 0,12%. There is a big difference between the sexes: in the adult male the total iron is about 50 mg. per kg. body-weight. But in the adult female the figure is only 35 mg. per kg., mainly be cause the normal blood-level of hemoglobin is lower than in the male. Iron exists in the body mainly in two forms: firstly, as heme in hemoglobin, and cytochrome concerned with the utilization of oxygen; and secondly, bound to a protein without heme formation, as storage and transport iron. Iron in the body has a very rapid turnover, since some 3 million red blood cells are broken down per second and the greater part of the iron released is returned to the bone marrow and re-formed into fresh hemoglobin; some 6,3 g. of hemoglobin containing 21 mg. of iron is handled this way every 24 hours.

The amount of iron in the body is regulated by control of absorption, since excretion is very small. The amount of iron absorbed from food differs with different foodstuffs, so the com position of the diet is important. Absorption can be increased in the normal Individual when the blood-hemoglobin is lower than normal and is the iron stores are low. Iron stores are normally lower in women than men and so they tend to absorb more iron. Iron absorption can decrease in older persons, especially in those over 60. Many estimates have agreed that the average Western diet pro vides between 10 and 15 mg. of iron daily, of which only 5-10% is absorbed.

Iron absorption takes place mainly in the upper jejunum, though some is absorbed in all parts of the small intestine and even in the colon. Iron in food is mostly in ferric form and must bе reduced to the ferrous form before it can be absorbed; this reduction begins in the stomach – though very little is absorbed there – and continues in the small intestine. The iron is absorbed via the brush-border of the intestine and then may take one of two paths; it is either passed into the blood, where it combines with a globulin, and passes to the marrow or to storage sites; or it combines with the protein, which is then deposited in the intes ti-nal cells.

Iron is lost mostly through the gastrointestinal tract by way of red cells and intestinal cells containing iron lost in the constant desquama-tion from the intestinal mucosa.

Fat factor

An enzyme abnormality has been discovered in the red blood cells of people who are overweight. It's the first clue that obe sity in humans may bе caused by a biochemical defect – not simply by overeating.

Researchers found that obese people have lower levels of a special enzyme that functions as a pump, transporting potassium and sodium in and out of cells. They suggest that with low levels of this pumping enzyme, less energy is used. Thus fewer calories are burned up as heat, while more are stored as fat.

New words

act – акт three – три

stage – стадия

first – начальный

voluntary control – добровольный контроль

soft – мягкий

mass – масса

mastication – перетирание

position – положение

root – корень

lingual muscles – языковые мускулы

second – секунда

brief – резюме

occupied – занятый

guiding – руководство

movements – движения

purely – просто

nature – природа

seized – захваченный

peristaltic – перистальтический

wave – волна

traveling – путешествие

along – вперед

before – прежде

cardiac sphincter – сердечный клапан

total – общее количество

amount – количество

iron – железо

varying – изменение

hemoglobin – гемоглобин

storage – хранение

myоglobin – миоглобин

fraction – фракция

together – вместе

body-weight – масса тела

Present Perfect Tense (действие, совершившееся в прошлом, связано с настоящим).

Спряжение глагола to write в Present Perfect Tense Таблица 13

Запомните типичные для Present Perfect обстоятельства: already, not yet, just, ever, never.

Сравните также:

I have bought a book today (this week, this month) – неистекший отрезок времени – Present Perfect.

I bought a book yesterday (last week, last month) – истекший отрезок времени – Past Simple.

Запомните также следующие предложения.

I have never been to France.

Have you ever been to London?

I haven't seen you for ages.

I haven't met him for a long time.

I haven't been to Moscow since last year.

В следующих предложениях измените время глагола на Present Perfect. Переведите предложения на русский язык

1. I am eating my breakfast.

2. We are drinking water.

3. He is bringing them some meat and veg etables.

4. You are putting the dishes on the table.

5. They are having tea.

6. She is taking the dirty plates from the table.

7. The children are putting on their coats.

8. The pupils are writing a dictation.

9. My friend is helping me to solve a difficult problem.

10. I am learning a poem.

11. She is telling them an interesting story.

12. Kate is sweeping the floor.

13. The waiter is putting a bottle of lemonade in front of him.

14. Susan is making a new dress for her birthday party.

15. She is open ing a box of chocolates.

16. They are writing a dictation.

17. I am drawing a picture.

18. She is cooking dinner.

19. We are dancing.

20. They are jumping.

Answer the questions.

1. Into how many stages is the act of swallowing divided?

2. Is the first stage under voluntary control?

3. What is the second stage in the act of swallowing?

4. Through what in the second stage the food is guiding?

5. What does the third stage in the act of swallowing involve?

6. How is the normal position of the empty human stomach?

7. How are shaped the majority of normal stomachs?

8. How can absorption be increased?

9. Who has normally lower stores of iron?

10. Where is iron lost mostly?

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?