D. Hildbrand
The action of the human heart (The cardiac cycle)
The introductory part of the film shows the beating of the human heart. You already know that it beats about 70 times a minute for about 70 years on average which amounts to 3 billion heart beats in a lifetime.
The second part illustrates its position and function within the circulatory system. Its job is to pump the blood through the blood vessels and around your body. That's why it is situated in the centre of your thorax, protected from injury by the ribcage. The right side of the heart receives deoxygenated blood from the different parts of the body. First it flows into the right atrium, then it is pumped into the right ventricle and then out through the pulmonary artery to the lungs. Here the red blood cells release carbon dioxide to be exhaled and are loaded with oxygen. After being oxygenated again the blood returns to the left atrium by way of the pulmonary vein. Then it is pumped into the left ventricle and the aorta carries the oxygenated blood away from the heart to all the major organs of the body where gaseous exchange takes place a second time: Here the blood gives up its oxygen and picks up the carbon dioxide released by the cells of these organs.
This survey of the circulatory systems is necessary for the understanding of the action of the heart. Please watch the next part of the film closely and take notes. It illustrates the cardiac cycle of the right part of the human heart which receives deoxygenated blood from the organs of the body and pumps it to the lungs. The cardiac cycle consists of two major actions of heart muscle: Contraction = systole and relaxation = diastole.
First the right atrium contracts, the cuspid valves are opened and blood is squeezed into the right ventricle. This ventricle is in a relaxed state so that it can receive blood.
Second the right ventricle contracts. As a result of the increasing blood pressure in this ventricle, the cuspid valves are closed so that the blood can't flow back. The pocket valves, however, are opened so that the blood is squeezed into the pulmonary artery.
Afterwards the atrium as well as the ventricle relax for about half a second. At the same time blood is drawn into the atrium from the vena cava superior and inferior.
Keep in mind that the blood can only flow in one direction as they only open in one direction like a one-way traffic system.
Words given
to amount to - sich belaufen auf
to exhale - ausatmen (opposite: to inhale)
to squeeze into - hineinpressen
Coronary heart disease and its causes
This last part of the film about the human heart deals with coronary heart disease and its causes. First the difference between the heart of a top athlete such as along distance runner and an average person is illustrated. An x-ray of their hearts shows clearly that regular exercise makes the heart muscle grow and protects people from coronary heart disease.
Coronary heart disease is a disorder of the coronary arteries that supply blood to the heart muscle. If these are damaged or blocked, the oxygen supply to a small or large part of the heart muscle is reduced or blocked, the heart stops contracting, and the person has a heart attack.
Most coronary heart disease starts with the build-up of a substance called cholesterol on the inside of the coronary vessels. This reduces the diameter of the vessels and may eventually block them or more usually cause blood clots to form which get stuck in the narrowed areas and cut off the blood supply.
Anybody can suffer from a heart attack but the main risk factors are smoking, high blood levels of fatty substances like cholesterol and a high blood pressure. People who smoke one packet of cigarettes a day run a double risk suffering a heart attack. Nicotine, one of the many dangerous substances cigarette smoke contains narrows the blood vessels so that your heart has to work harder to supply your organs with blood and your blood pressure increases. Moreover it increases the levels of fatty substances like cholesterol in the blood and, therefore , the likelihood of blood clots forming.
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