How the heart works

On day 18 in a tiny lump of cells, which is the human embryo at this time, the heart begins to beat and does not stop until our death. How the heart works is perhaps the only organ that never escapes from work. At the adult person heart for a day has time to pump 6-10 tons of blood, and during a life through it will pass 150-200 thousand tons. For 100 years of human life, the heart manages to make 4-5 billion cuts! And while it's great, it's easy to cope with this huge work.

How the heart works is perhaps the only organ that never escapes from work

Life on our planet, as you know, originated in the ocean, which to every cell of the body of the first creatures delivered food and oxygen. But the sea water was not the best vehicle and multicellular creatures, they wanted to have their own "ocean-aquarium", the waters of which would wash the cells of their body. Now in our "aquariums" splashing blood.

To drive the water of the internal "aquarium" had to acquire muscle pumps. At first it was just a pulsating vessel, the most simply arranged heart, which hemolymph was distilled into smaller vessels, and from there into interstitial and intercellular spaces. After washing them, she returned to the pulsating vessel.

To man and the higher animals, to push through the blood through the capillaries, a considerable force is needed. After all, we have 100-160 billion capillaries, and their total length is 60-80 thousand kilometers. It is necessary to create a sufficiently high pressure. For example, in a rat it is 75, in humans 120-140, and in a horse, even 200 mm of mercury.

For most animals living on earth, the two most important organs - the brain and the heart - are on the same level. This is very convenient: no additional effort is required to supply the brain with blood. Another thing is a man whose brain is located much higher than the heart, or giraffe, whose heart is located 2-3 m below the brain. All such beings have high blood pressure. But the higher the pressure, the greater the probability of an accident.

To ensure that the pressure in the system does not exceed the norm, there are special control organs - baroreceptors. The most important of them are located in mammals in the arch of the aorta, in carotid sinuses of carotid arteries, which carry blood to the brain, at the atria and at the ends of the pain nerves. On the slightest change in pressure, they immediately signal to the medulla oblongata, which gives the appropriate commands to correct the disorder. Restoration of normal pressure is carried out not so much by the activity of the heart, as with the help of blood vessels. The walls of small vessels - arterioles are equipped with muscles and easily change their lumen.

But what causes the heart to contract? Who orders the heart of the embryo to start working? He still does not even have a hint of the brain. It turns out that the heart can do without the commands of the brain. That is, our heart works on its own initiative, changing the force of contraction, depending on the volume of blood in it.

Yet, without the supreme command of the brain, well-coordinated work can not go. In the cardiac muscle, there are no nerves, and orders spread simply over the muscle fibers at a rate of 1 m per second. For normal atrial contraction, this speed is sufficient. The larger ventricles of the heart required a faster command transmission system - Purkinje fibers, through which excitation spreads 5-6 times faster.

Well-coordinated work of the human heart can be disturbed by various diseases. Sometimes it becomes impossible to switch excitation from the atria to the ventricles. In this case, the ventricles of the heart begin to contract much less frequently than usual, and they can stop working altogether.

More recently, doctors were completely helpless before this disease. In the second half of the 20th century. managed to create a miniature electrostimulator that gave commands to the heart, causing it to contract. For this, the patient was opened a thorax and, having reached the heart, implanted into it electrodes connected by thin wires with a stimulator.