Major and minor circulation

The circulatory system is responsible for pumping, transporting and distributing blood throughout the body. It is made up of its main organ, which is the heart, and blood vessels , which are made up of veins, arteries, and capillaries.

This circulatory system is made up of two circuits: the major or systemic circuit and the minor or also called pulmonary circuit . The first circuit is the one that is responsible for transporting and distributing blood throughout the body and then returning it to the heart, which is why it is called major since it encompasses the entire body. The short circuit is the one that carries blood from the heart to the lungs and then back to the heart.

Below we will detail both circuits in order to understand their operation, characteristics and routes.

Circulatory system      

As we described, the circulatory system is responsible through the blood vessels to transport and distribute blood throughout the human body.

This system is made up of the heart, veins, arteries, and capillaries.

Heart

The heart is a muscular pump and considered the center of the circulatory system. It is considered that it usually beats between sixty and one hundred times per minute. In each heartbeat it sends blood throughout the body, thus managing to transport oxygen to all cells.

It has four cavities that are located two in the upper part and another two in the lower part. Within the lower chambers we find the right ventricle and the left ventricle . They pump blood out of the heart.

In the two upper cavities we find the right atrium and the left atrium . They are the ones that receive the blood that enters the heart.

The main function of the heart is to pump blood from the ventricles to the body and to the lungs, and to receive it through the right and left atria.

Arteries

The arteries are the blood vessels responsible for carrying blood from the heart throughout the body. They have a thick intermediate muscular layer, which gives them the characteristic of being elastic. All arteries except the pulmonary, distribute oxygen-rich blood.

Veins

The veins are responsible for carrying blood to the heart. Unlike arteries, they are very inelastic, which is why they need to have internal valves to prevent blood from returning. All veins, except the pulmonary, conduct blood with little oxygen.

Blood capillaries

Blood capillaries are very thin vessels, which originate from the branches of the veins and arteries and join the end of the veins with the beginning of the veins.

The circulatory system is divided into a double closed circuit . It is called this way since the blood passes twice through the heart and without mixing the blood from the veins with the blood from the arteries. Each one goes through its conduit.

These two circuits are called the major or systemic circuit and the minor or pulmonary circuit . Both occur simultaneously but have different objectives and involve different sectors of the heart.

Greater circulation

The major or systemic circulation is called the route that the blood makes from the heart to the rest of the body and back to the heart. The name is assigned to it since it is the circuit that travels the greatest distance through the human body.

Its main function is to feed all tissues by distributing blood rich in oxygen and nutrients that are essential for cellular metabolism.

The journey of the major circuit begins in the left ventricle of the heart. There the blood leaves directly from the main artery called Aorta and spreads through the body through the other arteries, which then become smaller and become the blood vessels called capillaries that surround all the tissues.

Once they reach the tissues, the cells take up nutrients and oxygen and release carbon dioxide which will then be eliminated through respiration.

Then the blood begins its journey back through the venules, pooling the deoxygenated blood in the larger and larger veins until it reaches the superior and inferior vena cavae. This tour ends in the right atrium of the heart.

The major circulation circuit covers 85% of the total volume of blood in the body, which is distributed 64% in veins and 13% in arteries.

Summarizing its main functions we find:

• It is responsible for the distribution of oxygenated blood to the tissues
• It is responsible for sending deoxygenated blood back to the heart
• Collects waste substances from tissues
• It deals with the distribution of hormones from the production organs to the target organs.

Less circulation

This circulation is also called pulmonary and is responsible for transporting deoxygenated blood and carbon dioxide to the lungs. Once there , gas exchange is generated to remove carbon dioxide from the body and replace it with the oxygen that enters with the air. In this way, the blood can become oxygenated to join the larger circuit.

The minor circulation circuit begins in the right ventricle of the heart with the blood that the right atrium drains from the body and, after crossing the pulmonary valve, reaches the pulmonary artery. Once in it, it then branches to distribute the blood in the two lungs, which are located one on each side of the heart.

When it reaches the lungs, the blood begins the process of gas exchange. Once it is oxygenated, it begins its way back to the heart through the pulmonary veins which connect with the left atrium, ending its cycle and moving on to the greater circuit.

The time that the blood remains in the lungs is 0.8 seconds, which means that in less than 1 second the blood performs the gas exchange: it discards the carbon dioxide and is charged with oxygen to be able to return to the heart.

This minor circulation circuit covers 16% of the total volume of the blood, of which 7% is from the heart and 9% from the lungs.