William Harvey and the discovery of the blood circulation

Harvey, who was exposed during his studies to the scientific approach of Galileo and others, developed a scientific research approach according to which an assumption must be doubted until it has been proven correct through experiment and research.

William Harvey He was born on April 1, 1578 and his birthday is an excellent reason to remember one of the greatest revolutions in science - the discovery of the blood circulation.

In ancient Greece, the study of the body was done with the help of dissecting corpses. This is how Aristotle and Plato learned about the internal structure of the body and the existence of the arteries and veins. In her body, the arteries are empty of blood, while the veins are full of blood. From here it was easy to understand that the role of the veins is in blood flow, but the role of the arteries was still unclear.

In the second century AD, the physician Galanus continued to investigate and it was he who stated that blood also flows in the arteries but believed that the blood is created in the liver and passes to the heart where it becomes "spiritual" and "pure" with the help of the air from the lungs. Today it is known that the blood cells are formed in the bone marrow and the role of the lungs is to replace carbon dioxide with oxygen. Galanus noticed that the heart was divided into two parts, right and left, but believed that the blood passed between the sides through small holes. Today we know that the passage of blood between the two parts of the heart exists only in fetuses and the septum between them closes at birth.

Harvey was born in England and studied medicine in Cambridge. During this period it was customary to learn only from books, without experiments or analyses. Although there are advantages to this approach - it shortens the learning process since the answer is already known, saves killing animals, and in general there is not much point in repeating the same experiment thousands of times when you already know the result. But it contains a serious drawback - if the textbooks contain an error, we are doomed to repeat mistakes and avoid the progress of knowledge.

Harvey, who was exposed during his studies to the scientific approach of Galileo and others, developed a scientific research approach according to which an assumption must be doubted until it has been proven correct through experiment and research. Some of his experiments involved the analysis of animals, which were not always completely dead. (who said an "anesthetized" frog And didn't he?) During these surgeries, Harvey saw the contractions of the heart and got the idea that the heart works as a pump. In addition, he noticed that in birds and mammals the septum that separates the two parts of the heart is sealed and does not allow blood to pass through it.

Back in the time of Glenus, they knew how to distinguish between arteries and veins according to the thickness of their wall, but believed that their function was the same. Harvey was the first to show that in veins there are thin folds of tissue that act as valves that allow blood to flow in one direction only. Until that time, the thinking was that the flow in the blood vessels is in both directions.

To prove his hypothesis Harvey conducted an experiment that you can try yourself.

Choose a guinea pig with prominent veins (for men it's easier, especially if their fat percentage is relatively low). On the arm, find a beautiful vein and choose two points on it - one close to the heart (elbow) and the other far (toward the palm). Press on the point farthest from the heart and stop the blood flow. With the help of a finger from the other hand, they push the blood in the vein towards the heart and in fact empty the vein of blood. You can really see how where before there was a blue line now it has disappeared. When we release the finger closest to the heart (to the elbow) the vein will remain empty. When we release the finger far from the heart, the vein will immediately fill with blood and the characteristic blue color will return.

Conclusion - the blood in the veins flows in one direction: from the body to the heart.

Another hypothesis that Harvey faced was the belief that the blood is shed in the tissues and disappears and completely new blood is created all the time. Harvey chose an unconventional way for his time to deal with this hypothesis - mathematics.

Harvey made a simple calculation: the heart capacity of an adult person is about 70 ml. Average heart rate for an adult is about 70 beats per minute.

That is, 4.9 liters of blood leave the heart per minute. (70x70 = 4,900) per day is already about 7,056 liters of blood. Since it is not possible for the body to regenerate such a large amount of blood, the blood must flow in a closed circulation, meaning that we use the same blood.

Harvey concluded that the blood starts a flow cycle from the heart, to the arteries, from there it reaches the veins and returns to the heart.

He had one problem - how does the blood get from the arteries to the veins?

For this, it was necessary to wait for a little more development of the microscopes, so an Italian researcher named Malpighi identified the capillaries and finally confirmed Harvey's hypothesis.