The pulmonary artery departs from the right ventricle and soon forks into the right pulmonary artery and left pulmonary artery, which go to their respective lungs.
Once inside the lungs, both divide into as many branches as are the pulmonary lobes; after further subdivision at the level of the pulmonary lobes, these resolve into the pulmonary network.
The walls of the capillaries are very thin and the respiratory gases can pass through them easily: oxygen from the air can thus pass from the pulmonary acini to the blood; on the contrary, carbonic anhydride leaves the blood and enters the pulmonary acini, to be released later. The capillaries follow the venules that come together until they form the pulmonary veins. These follow the course of the arteries and launch into the left atrium. The pulmonary artery contains dark blood, overloaded with carbon dioxide (venous blood). In contrast, the pulmonary veins contain blood that has left carbonic anhydride and is charged with oxygen, turning red (arterial blood).
The great circulation
The aorta, starting point of the great circulation, part of the left ventricle. It forms a large arch, which runs back and to the left, runs vertically downward, following the spine, then crosses the diaphragm and enters the abdominal cavity. At the end of its course, the aorta divides into two iliac arteries, which go to the lower limbs. From the aorta there are numerous branches that carry the blood to various regions of the body. From the aorta the subclavian arteries go to the upper limbs and the carotid arteries carry the blood to the head. From the thoracic aorta depart the bronchial arteries, which go to the bronchi and lungs, the esophageal arteries and the intercostal arteries.