Physiology of the cardiovascular system

The contractions of the heart pump the blood through the arteries to all the parts of the body. The total weight of the blood pumped by the heart daily is about ten tons. In the adult the heart makes from 60 to72 beats per minute. The rate of heartbeat depends on age, physical activity and emotions.

Each wave of heart contraction and a period of rest following it compose a cardiac cycle. Each cardiac cycle consists of three phases: the phase of short contraction of both atria is called the atrial systole; the phase of a more prolonged contraction of both ventricles is called the ventricular systole. The period of rest of the cardiac muscle is called the diastole.

The left ventricle discharges out the blood received by the left atrium from the pulmonary circulation through the aorta to the systemic circulation.

The blood received from the systemic circulation by the right atrium is discharged out of the right ventricle to the lungs through the pulmonary arteries.

Blood is a fluid tissue with many various functions. Blood is composed of plasma and the corpuscular elements which are called red corpuscles or erythrocytes, white corpuscles or leucocytes and blood platelets or thrombocytes.

The count of leucocytes in the blood of a healthy person is 4,500 to 9,500 per cu mm (cubic millimetre). The erythrocytes are the most numerous cellular elements, ranging from 4,000,000 to 5,000,000 per cu mm. They have great elasticity and flexibility which give them the possibility to pass through very small capillaries. Red cells contain red colouring substance or hemoglobin.

The total blood volume is divided into circulating and reservoir volumes. The average human blood volume is 8-10% of the body weight. When we listen to the heart we can hear two or sometimes three sounds. The first heart sound is greater over the surfaces of the ventricles, of the mitral and tricuspid valves. The second heart sound is heard loudest over the aorta and the pulmonary artery. The third sound is heard when the blood is passing from the atria into the ventricles.

II. Работа над грамматикой.

Задание 1. Измените залог предложения:

1. The septum divides the heart chambers.

2. The atrioventricular valves separate the atria from the ventricles.

3. The vessels carrying blood to and from the tissues of the body compose the general system.

4. The veins passing to the liver form the portal system.

5. Students passed a test yesterday.

6. A doctor will examine the patient tomorrow.

Задание 2. Поставьте глагол в нужной форме пассивного залога

1. The oxygen (to take up) from the air in the lungs. 2. This process (to call) external respiration. 3. A doctor found that the patient’s airways (to block) by a foreign body. 4. The respiratory activity (to govern) by the amount of carbon dioxide which previously (to eliminate) from the organism. 5. The lung X-ray (to perform) next week. 6. The movement of the air (to cause) by an increase in the volume of the thoracic cavity. 7. I am sure that during the operation the outer layer (to raise) to provide the necessary space. 8. The thorax (to separate) from the abdomen by the diaphragm.