Text A. Work of the human heart

The human heart contracts from the first moment of life until the last one. The contractions of the heart pump the blood through the arteries to all parts of the body. Scientists have determined that the total weight of the blood pumped by the heart daily is about ten tons. The rate of heart contractions is regulated by two groups of nerve fibers. It varies in different persons and at different age.

Physiologists have determined that in the adult the heart makes from 60 to 80 beats per minute. In children the rate of heartbeat is much higher. Research work of many scientists has helped to determine that the rate of heartbeat increases depending on different emotions.

Each beat of the heart is followed by a period of rest of the cardiac muscle. Each wave of contraction and a period of rest following it compose a cardiac cycle. Each cardiac cycle consists of three phases: physiologists have called the first phase of short contraction of both atria – the atrial systole. They have called the second phase of a more prolonged contraction of both ventricles – the ventricular systole. The period of rest of the cardiac muscle is called – the diastole.

During the systole of the ventricle the blood is pumped from the right ventricle into the pulmonary artery. When the right ventricle has pumped the venous blood into the pulmonary artery it enters the pulmonary circulation. The blood is brought to the lungs. In the lungs the venous blood discharges out carbon dioxide. When the blood has discharged out carbon dioxide it takes in oxygen in the lungs. The blood which has become oxygenated passes from the pulmonary veins to the left atrium of the heart.

Under the pressure of the left atrium the arterial blood which the pulmonary veins have brought to the heart is pumped into the left ventricle. During the prolonged contraction of the left ventricle the arterial blood is pumped into the aorta – the main artery of the vascular system. When the left ventricle has pumped the arterial blood into the aorta it is carried through the arteries to all the parts of the body.

Prolonged research work of many physiologists has given the possibility to estimate the role of the ventricles which serve as the main pump. The atria act as receiving chambers.

TASKS

I. Translate the following word combinations:

общий вес крови, частота сердечных сокращений, две группы нервных волокон, 60 ударов в минуту, частота сердцебиения возрастает, в зависимости от различных эмоций, период расслабления сердечной мышцы, сокращение обоих предсердий, более длительное сокращение желудочков, кровь поступает в малый круг кровообращения, кровь выделяет углекислый газ, под давлением, главная артерия сосудистой системы, возможность оценить роль, служить в качестве основного насоса, принимающие камеры

II. Make up questions to the underlined words:

1. In the adult the heart makes 60-80 beats per minute.

2. Each beat of the heart is followed by a period of rest of the cardiac muscle.

3. Each wave of contraction and a period of rest following it compose a cardiac cycle.

4. Physiologists have called the first phase of short contraction of both atria – the

atrial systole.

5. Under the pressure of the left atrium the arterial blood is pumped into the left

ventricle.

III. Answer the questions:

1. What is the total weight of the blood pumped by the heart daily?

2. What is the rate of heart contractions regulated by?

3. What does the rate of heart contractions depend on?

4. What is the atrial systole?

5. What is the ventricular systole?

6. What is diastole?

7. What does the blood discharge out in the lungs?

8. Where does the blood take in oxygen?

9. What is the aorta?

10. What is the role of the ventricles?

11. What is the role of the atria?

IV. Describe how blood circulates in the body: