First a few facts:
When resting, the human heart beats around 70 times per minute and pumps around five liters of blood through the body. It does this constantly – day and night. Depending on the activity, performance changes; under strain it beats up to 180 times per minute and pumps up to 25 liters of blood. Over a lifetime, this means around 180,000,000 liters of blood, which are transported through the body by the heart and supply all organs with blood.
The heart is the most important organ and is developed in the embryonic stage within the first three weeks.
The function of the heart is comparable to that of a pump, but the system is more complicated than it seems at first glance because the heart serves two different circuits. There is the small circuit that starts from the right side of the heart and pumps oxygen-poor blood through the lung circuit. The oxygen-rich blood flows back into the left half of the heart, from where the blood is transported in the so-called large circulation through all organs of the body and supplies them with oxygen.
These two pump systems are necessary because the pressure conditions in the systemic circulation are different than in the lungs. Both halves of the heart consist of two chambers, which are separated from each other by the cardiac septum. The first chamber (the atrium) sucks in the blood, the second (the actual chamber) expels the blood. The blood is collected in the atria and then pressed into the circulation from the chamber behind it; a constant alternation of tension (systole) and relaxation (diastole) takes place.
The heart valves, which function like check valves, ensure the precise distribution of blood throughout the body. A distinction is made between leaflet and pocket valves (tricuspid valve and pulmonary valve).
The leaflet valves are located between the atrium and the ventricle and are pressed together during systole so that they close the ventricle to the atrium and prevent blood from flowing back. The pocket flaps at the chamber exit also open and, after the blood has been expelled, are automatically closed by the weight of the blood flowing back. As a result, blood cannot flow back into the heart during diastole. The heart valves generate the vibrations that can be heard in the chest as heart sounds.
Within the thorax, this construct is protected by the so-called pericardium. This is filled with a liquid and thus prevents friction that could otherwise arise from the constant movements of the heart. (EK)