In the right atrium we can observe the openings of superior and inferior venacava. In the left atrium, we can observe the openings of pulmonary veins, that bring blood from lungs.

From the upper part of the left ventricle, a thick blood vessel called aorta arises. It supplies oxygenated blood to the body parts. From the upper part of the right ventricle pulmonary artery arises that supplies deoxygenated blood to the lungs. After careful examination we can observe valves in the pulmonary artery and aorta as well

Let us study how we came to know about the structure and functions of the blood vessels.

It was not until 16th century that we really came to know how our vessels functioned. In 1574, an Italian doctor, Girolamo Fabrici, was studying the veins in the leg. He noticed that they had small valves in them. If the blood moved in one direction, the valves folded towards the walls of the vessel, so that the blood could pass without trouble. If the blood moved in the opposite direction, the valves closed.

This meant they are one-way valves. The valves permitted the blood to move even when a person is standing upright. But not move downward.

When a person moves his legs, or just tightens his leg muscles, those muscles squeeze the veins and force the blood in those veins to move upward against the pull of gravity (because that’s the only way to go). If a person keeps his leg muscles relaxed, the blood isn’t moving much, but at least it isn’t being pulled down by gravity. The valves won’t allow that.

Everyone thought that the blood leaving the left ventricle always moved away from the heart for which Fabrici paid no attention. He missed the importance of his own discovery. But then, William Harvey (1578-1657), an Englishman who, after he became a doctor, went to Italy for further education and studied under Fabrici.

Harvey dissected the hearts of dead people and studied the valves
between each atrium and its ventricle. He noticed that they were oneway valves. They allowed the blood to flow from the atrium to thetricle without any hinderance.

When the heart contracted, however, no blood in the ventricle could flow back into the atrium. Instead, all the blood was pushed out into the arteries.

Harvey began thinking about the valves his teacher, Fabrici, had discovered in the leg veins. They were one-way, and they forced the blood to move toward the heart