he heart is two powerful pumps – the left and right heart. They both pump blood through a closed system consisting of blood vessels. A heart Is a doubled twin muscle lined with epithelium and weighing 300 g. Every minute it contracts 60 to 70 times, pumping at every contraction of 0.075 L of pulmonary blood from the left heart into the aorta and as much venous blood from the right heart into the lungs. It turns out that every day the heart pumps 15,000 liters of blood through the capillary network and is cut 100,000 times. And this is the average burden on the heart. When we exert all the forces, it can work five times faster than usual. That’s why a tiny organ – its weight is not even 0.5% of the body weight of a person – consumes 20% of the oxygen we breathe and 10% of all the oxygenated blood of the lung enters the heart muscle, and does not spread through the body.

Two pumps – the left and right heart – pumped the blood in a circle. In all highly developed organisms, these two – in principle independent – organ merged, forming a single whole of organisms.The human heart is a hollow muscular body the size of a fist. By coronary vessels it is supplied with blood. The brain controls any of our muscles except the heart muscle – it has its own control center – a sinus node. So scientists call the accumulation of nerve cells in the wall of the right. The size of this node is only a millet grain. He commands the heart muscle with electrical signals.
With each contraction of the heart throughout the body, electrical current flows. If you register these signals. we get a curve called an electrocardiogram (abbreviated as ECG). When studying the ECG, the doctor determines whether the heart works normally.

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