The pulmonary circulation is a vital system in our body that acts as a bridge between the respiratory and cardiovascular systems. It serves as a transport network for deoxygenated blood from the heart to the lungs and then returns oxygen-rich blood back to the heart.

The process begins with the right ventricle of the heart pumping deoxygenated blood into the pulmonary trunk. This large vessel extends about 5 centimeters before splitting into the left and right pulmonary arteries. These arteries carry the deoxygenated blood into the lungs, where they further divide into lobar arteries, three in the right lung and two in the left.

Within the lungs, the lobar arteries continue to branch out, forming smaller vessels known as pulmonary arterioles. These arterioles play a crucial role in delivering blood to the capillary networks that envelop the alveoli, the tiny air sacs in the lungs where gas exchange occurs.

As the deoxygenated blood flows through the capillaries surrounding the alveoli, it releases carbon dioxide and absorbs oxygen during respiration. This newly oxygenated blood then departs the alveoli via small veins or venules.

These venules converge to create four pulmonary veins, two originating from each lung. These veins carry the oxygen-enriched blood back to the heart, specifically to the left atrium. This marks the completion of the pulmonary circuit, readying the oxygen-rich blood for distribution to the rest of the body.