Unit 15

Pre-text assignments

1 Learn the key words and phrases:

cardiovascular system, circulatory system, nutrients, excretory organs, target tissues, favourable cellular environment, viscous, platelets, blood sample, cellular wastes

2 Match the following English word combinations with the Ukrainian ones:

1) red blood cells a) згортання крові

2) to combat infection b) підтримувати

3) to destroy bacteria потрібну кількість крові

4) the clotting of blood с) червоні кров’яні тільця

5) to maintain an adequate d) боротися з інфекцією

blood volume e) знищувати бактерії

3 Translate the following:

1 The cellular fraction consists of red blood cells, white blood cells and blood platelets. 2 The normal coagulation time is from three to five minutes. 3 Plasma is the fluid portion of the blood.

Blood

The blood, heart, and blood vessels constitute the circulatory system and provide a link between the body's internal parts and its external environment. More specifically, the blood transports nutrients from the digestive tract, oxygen from respiratory organs to the body cells, and carries wastes from these cells to the respiratory and excretory organs. It transports hormones from the endocrine glands to target tissues and bathes the body cells in a liquid of relatively stable composition. It also aids in temperature control by distributing heat from the skeletal muscles and other active organs to all the body parts. Thus, the blood provides vital support for cellular activities and aids in maintaining a favorable cellular environment. The heart and the closed system of blood vessels comprise the apparatus that moves blood throughout the body. These organs constitute the cardiovascular system.

Blood is a type of connective tissue whose cells are suspended in a liquid intercellular material. It plays vital roles in transporting substances between the body cells and the external environment, and it aids in maintaining a stable cellular environment.

Whole blood is slightly heavier and three to four times more viscous than water. Its cells, which are formed mostly in red bone marrow, include red blood cells and white blood cells. The blood also contains cellular fragments called platelets.

The volume of blood varies with body size. It also varies with changes in the fluid and electrolyte concentrations and the amount of fat tissue present. However, an average-sized male (70 kilograms) will have a blood volume of about 5 liters.

If a blood sample is allowed to stand in a tube for a while, the cells will become separated from the liquid portion of the blood and settle to the bottom. This separation can be speeded by centrifuging the sample so that the cells quickly become packed into the lower part of the centrifuge tube. When the amounts of cells and liquid are measured, the percentage of each in the blood sample can be calculated.

A blood sample is usually about 45% cells. This percentage is called the hematocrit (HCT), or packed cell volume (PCV). The remaining 55% of a blood sample consists of clear, straw-colored plasma.

In addition to red cells, which comprise over 99% of the blood cells, the solids of the blood include white blood cells and blood platelets. The plasma is composed of a complex mixture that includes water, amino acids, proteins, carbohydrates, lipids, vitamins, hormones, electrolytes, and cellular wastes.

Red blood cell production is significantly influenced by the availability of two of the B-complex vitamins – vitamin B₁₂ and folic acid. These substances are required for the synthesis of DNA molecules, so they are needed by all cells for growth and reproduction. Since cellular reproduction occurs at a particularly high rate in red blood-cell-forming tissue, this tissue is especially affected by a lack of either of these vitamins.

Iron is also needed for the synthesis of hemoglobin. Although much of the iron that is released during the decomposition of hemoglobin is available for reuse, some iron is lost each day and must be replaced.

White blood cells, or leukocytes, function primarily to control various disease conditions. Although these cells do most of their work outside the circulatory system, they use the blood for transportation to sites of infection.

Normally, five types of white cells can be found in the circulating blood. They are distinguished by their size, the nature of their cytoplasm, the shape of their nucleus, and their staining characteristics.

Post-text assignments

1 Complete the sentances:

1 The most numerous of the cellular elements of the blood are...

a) white blood corpuscles; b) red blood corpuscles; c) blood platelets

2 The blood is...

a) connective tissue; b) muscular tissue; c) fluid tissue; d) nervous tissue

2 Read the passages and answer the questions:

1 This substance is composed of plasma, red corpuscles, white corpuscles and platelets. What substance is it?

2 These cellular elements are the most numerous in the blood. They range from 4 to 5 million per cu mm in healthy adults. Their colour(ing) is red. What cellular elements are they?

3 Answer the questions using the thematic words:

1 What is the main function of the blood?

2 How are the products of metabolism removed from the tissues?

3 What components does the blood consist of?

4 What is the chief constituent of the red blood cells?

5 What are the major components of blood?

6 What factors affect blood volume?

7 How is hematocrit determined?

8 What vitamins are necessary for red blood cell production?

9 Why is iron needed for the normal development of red blood cells?

10 What are the primary functions of white blood cells?

4 Read and render the article:

Try this. Fill two caps half full with corn syrup. Stir two drops of red food coloring in each cup, so it looks like blood. Sprinkle one teaspoon of sugar in one cup and one teaspoon of flour in the other. Record how long it takes for the "blood" to absorb the sugar and flour. Which one was absorbed more quickly – the sugar or the flour?

5 Read and translate the text:

One of the scientific research Institutes carried out an interesting experiment. Six young persons – four men and two girls did not sleep for 124 hours. They were under the constant observation of the doctors who took their cardiograms, determined the pulse and blood pressure and carried out many other investigations.

Not to fall asleep they were allowed to do physical exercises, dance and play, but they were not allowed to take any stimulants. Vision, hearing and muscular reflexes were often examined during the experiment.

The experiment was successful. Its findings showed that prolonged sleeplessness increases the amount of sugar in the blood, decreases the level (amount) of vitamins B₁ and B₆, produces considerable increase of white boood cells and decreases the amount of iron in the blood.