Classification of the blood circulation | The human blood circulation

Classification of the blood circulation

The blood circulation is divided into a large circulation, the body circulation, and a small circulation, the lung circulation. In order to understand these two circuits, one must first understand the structure of the heart. The heart consists of two ventricles (ventricles) and two atria (atria).

The left atrium and left ventricle are also known as the left heart, while the right atrium and right ventricle are known as the right heart. The atria and ventricles of one side are separated by valves, the so-called sail valves. These valves open only under the pressure of the heartbeat, otherwise they are closed so that the blood cannot flow back again.

In the great circulation, starting from the left ventricle, which contains oxygen-rich blood, this blood is pumped into the subsequent aorta during a heart action (heartbeat). To do this, the blood must pass through the aortic valve, which is opened by the pressure and otherwise closed. From here the blood can reach the entire body and all organs.

As described above, the blood flows from there through the veins back to the heart. The connection to the heart is made by the largest veins, the superior and inferior vena cava, which open into the right atrium from above and below respectively. The superior vena cava has previously collected the venous blood, i.e. the blood low in oxygen, from the head and neck region, the inferior vena cava that from the body.

Here, in the right side of the heart, there is therefore blood with a low oxygen content. From the right atrium the blood is pumped through the tricuspid valve (right AV valve) into the right ventricle. Since the blood is low in oxygen and nutrients, it must first be enriched with oxygen and nutrients again before it can supply the body with it again.

This is done in the small circulation, the pulmonary circulation. The pulmonary circulation starts from the right ventricle of the heart. From there, the venous blood is led into the pulmonary artery (arteria pulmonalis), which is closed by the pulmonary valve when at rest.

Through the pulmonary artery, the blood is directed to the lungs so that the accumulation of nutrients can take place there. For this purpose, the lung also has a vascular system, which is made up of arteries, capillaries and veins, just like the body’s circulation. The arteries in the lungs, which are becoming more and more branched, are here accompanied by the bronchi, which transport the air from the respiratory tract.

The mass transfer takes place in the smallest vessels, the capillaries, as this is where the lowest flow velocity is reached. The capillaries are separated from the end sections of the airways, the alveoli, by a minimally thin wall. Via this thin wall (membrane) substances can migrate in both directions.

This is where oxygen from the alveoli is absorbed into the blood and carbon dioxide from the blood is released into the alveoli so that it can be breathed out. The oxygen-rich blood is then returned to the heart via the pulmonary veins (venae pulmonales). Here four pulmonary veins (two on each side) open into the left atrium. From there, they are pumped through the mitral valve (right AV valve) into the right ventricle of the heart, from where they are led back into the great circulation, the body’s circulation. The left heart contains, in contrast to the right heart, the oxygen-rich blood.