The blood circulatory system is an essential bodily system. Different independent systems work in coordination with each other to complete the process of blood circulation. These independent systems include the heart, lungs and arteries, veins, coronary and portal vessels. The system transfers oxygen, blood, nutrients and other gases and hormones from one part of the body to another. It ensures that these are delivered to each cell in the body. The blood is carried from the heart by the arteries and carried back to it by veins.
The circulation of blood in the body is a continual process. It happens when the heart relaxes between two beats. The blood flows from the upper chambers of the heart known as the atria into the lower chambers known as the ventricles which expand as a result.
There are two blood circulatory systems in the human body – the systemic circulation and the pulmonary circulation. The systemic circulation transfers blood to tissues, cells and organs so that they get essential nutrients and oxygen. The pulmonary circulation refers to the fresh oxygen we breathe that enters the blood.
In the systemic circulation the left ventricle transfers blood into the main artery. From the main artery the blood is transferred to the smaller and larger arteries and further to the capillary network. It is here that the blood releases the nutrients and oxygen and takes waste substances and carbon dioxide. The oxygen level decreases as a result and the blood accumulates in the veins. Post this, it travels to the right atrium and then to the right ventricle.
During the pulmonary circulation that occurs just after the systemic circulation, the blood is pumped by the right ventricle. The blood carries oxygen into the pulmonary artery that transfers it further into the smaller arteries and capillaries. The capillaries form a network around the pulmonary vesicles towards the end of the airways where the carbon dioxide releases from blood and oxygen enter it. This blood rich in oxygen travels to the left ventricle via pulmonary vein and left atrium.