One of my patients came one day with her daughter and complained about her being too weak to do anything. The child looked very thin. After our checks, she was diagnosed with a congenital heart defect and had surgery. She recovered. Her immobility, which had seemed to be laziness, was because her blood did not flow properly to her organs. 

Our circulatory system is how blood reaches our organs and muscles. The necessary blood flow for each organ is precisely adjusted to its needs. Failure in the proper flow of blood may cause many problems in our health and worsen the conditions of our overall wellbeing. The brain and heart are vitally important for our body, so the design of their mechanisms feature even more complexity than any other organ. For example, when you try to solve a difficult mathematical problem, the problem-solving area of the brain starts to work immediately. We can understand this by using fMRI (Functional Magnetic Resonance Imaging) films. Using fMRI, it is possible to see where activity increases in the brain. As activity increases, so, too, does blood flow to that part of the brain. Conversely, when we are asleep, brain blood flow significantly decreases. 

At rest, the amount of blood that goes to our muscles is around 1.2 liters per minute. Certain muscles can receive up to 20 times as much during intense sports activity. While doing sports, the organs of the abdomen, the kidneys, and the skin rest, allowing more blood to flow to the muscles, thus reducing the amount of blood they use. While exercising, the amount of blood pumped by the heart, to compensate for the excess blood needed by the muscles, is tripled. 

The heart is equipped with mechanisms that can adjust the amount of blood pumped according to the working quantities of the organs – and therefore, their blood needs. This is a complete automatic arrangement; it requires no thought or awareness from us.

If the heart cannot pump enough blood, it is called heart failure, and this means that the heart itself, as well as the brain, liver, kidneys, and all other organs, are not getting enough blood. Failure begins in the liver and kidneys. If the brain does not get enough blood, dizziness, fainting, and other disruptions occur. If the muscles can’t get enough blood, a patient is afflicted by fatigue, weakness, dementia, severe aches, and, of course, the inability to do work. 

If the heart pumps too much blood, then many diseases, especially hypertension, appear. This makes the heart tired, as it works too much – and once again, heart failure occurs. 

The heart pumps blood to the aorta, which is the largest artery. In the aorta, blood must flow very quickly, ensuring that the organs get the food and oxygen they need. The aorta has the highest blood pressure, since it is the first vessel that receives blood from the heart. The vein wall is created thick, elastic, and robust so that the high blood pressure doesn’t tear it apart.  As you move away from the heart, the number of vessels increases, the blood pressure decreases, and the blood starts to flow more slowly; the walls of the veins gradually get thinner. 

The capillaries are created with a great structure-function fit.  The capillaries, both themselves and their walls, are created to be very, very thin. At the end of arteries, just before the capillary vessels (arteriole), the blood pressure and velocity are reduced. The aim is to prevent the high pressure form damaging these very thin veins. In the capillaries, blood travels slowly. Why? Because these are the shopping veins. The body’s 100 trillion cells get all the oxygen, glucose, fat, protein, vitamins, antibodies, and hormones from these blood vessels. In addition, all cells give their carbon dioxide, urea, creatinine, uric acid, and all other waste products to the blood in the same capillary vessels. If the blood in the capillaries was as fast as in the big arteries, then the vessel could not withstand it, and the blood would tear away the walls without the cells getting their nutrients and without shedding their garbage. And if there was even a little scratch on our vessel, we would not be able to stop the bleeding. 

After passing through the capillaries, the blood is accelerated again in the small veins. There is more blood in the veins. The wall of the veins, which are deep below the skin’s surface, is thicker than the capillaries but thinner than the arteries. As the wall is thinner, the internal space is wider; the veins are a kind of bloodstream. The small veins connect to the main veins, which empty blood into the heart. In order to pump blood to the heart, the blood pressure of each pulse must be sufficient for all the blood in the body to be pumped back to the heart. Neither more nor less. The mean blood pressure of the heart is 100 mmHg. At the point where the blood circulating eventually reaches the heart, the mean blood pressure is 0 mmHg. As an example from daily life, it is like you hit a ball with your foot: as the ball reaches its target, its energy finishes and stays at the exact point you want. Our heart reaches the target with every stroke. Thus, at the point where the blood has already completed circulation, the pressure applied to it is zero. Thanks to this incredible adjustment, the heart does not waste power.