Занятие 14

TRANSPORT OF GASES IN THE BLOOD

V. Письменный перевод текста со словарем. Направлен на развитие компетенции ПК-48.- 45 мин

In the blood, oxygen and carbon dioxide are carried in different ways. Two-thirds of the carbon dioxide is transported in the plasma, about 5% of it being in solution and the remainder combined to form sodium bicarbonate; the remaining one-third is carried in the red blood corpuscles combined with haemoglobin, to form a loose compound called oxyhaemoglobin. As the blood moves slowly along the capillaries in the tissue, oxygen is given off from this compound to supply the needs of the cells, and carbon dioxide produced by the cells is taken up by the plasma. Both processes involve diffusion through the capillary wall. The pressure of carbon dioxide outside the capillary is higher than it is inside and so carbon dioxide is forced in; on the other hand, the pressure of the oxygen inside the capillary is higher than the pressure of the tissues, and so oxygen passes out.

The blood leaving the tissues is thus relatively poor in oxygen and rich in carbon dioxide.

This venous blood is returned to the heart and by it pumped through the lungs, where again it passes slowly through capillaries. These capillaries lie in the walls of innumerable tiny air spaces called alveoli, which contain air relatively rich in oxygen and poor in carbon dioxide. Here another process of exchange by diffusion takes place, in the reverse direction. The pressure of carbon dioxide in the capillaries is now greater than the pressure in their surroundings, so that carbon dioxide passes out into the air; conversely, oxygen passes in from the alveoli to the blood. The blood which leaves the lungs is therefore rich in oxygen and poor in carbon dioxide and this is what distributed throughout the body by the arteries. The difference between arterial and venous blood is visible to the naked eye, for oxyhaemoglobin is bright red and hemoglobin much darker in color. Venous blood is thus dark red but arterial blood is scarlet.

A third gas, nitrogen, is present in small quantities in solution in the plasma. It is completely inert; and its importance lies only in the fact that if the atmospheric pressure in which a man works is increased, more nitrogen is forced into solution.

Этапы занятий и рекомендуемая продолжительность тренировки видов речевой деятельности:

I. Речевая разминка. Пособие “Headway”. Student’s Book. Intermediate. Направлено на формирование компетенции ОК-6 - 30 мин

Дата добавления: 2014-12-07