Science, Tech, Math › Science How the Main Pulmonary Artery Delivers Blood to the Lungs Share Flipboard Email Print The pulmonary circuit deals with blood between the heart and the lungs. Purestock/Getty Images Science Biology Anatomy Basics Cell Biology Genetics Organisms Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated December 13, 2018 Arteries are vessels that carry blood away from the heart. The main pulmonary artery or pulmonary trunk transports blood from the heart to the lungs. While most major arteries branch off from the aorta, the main pulmonary artery extends from the right ventricle of the heart and branches into left and right pulmonary arteries. The left and right pulmonary arteries extend to the left lung and right lung. There are two main circuits in the body: the pulmonary circuit and the systemic circuit. The pulmonary circuit deals with blood between the heart and the lungs while the systemic circuit deals with the remaining parts of the body.While most arteries carry oxygenated blood in the body, the pulmonary arteries carry de-oxygenated blood to the lungs.The main pulmonary artery, or the pulmonary trunk, transports de-oxygenated blood from the heart to the lungs.The main pulmonary artery branches into both a right and left vessel. The right pulmonary artery carries blood to the right lung while the left pulmonary artery carries it to the left lung. The pulmonary arteries are unique in that unlike most arteries which carry oxygenated blood to other parts of the body, the pulmonary arteries carry de-oxygenated blood to the lungs. After picking up oxygen, the oxygen rich blood is returned to the heart via the pulmonary veins. Heart Anatomy and Circulation Heart image showing coronary vessels and pulmonary trunk. MedicalRF.com/Getty Images The heart is located in the thoracic (chest) cavity in a central compartment of the cavity known as the mediastinum. It is situated between the left and right lungs in the chest cavity. The heart is divided into upper and lower chambers called atria (upper) and ventricles (lower). These chambers function to collect blood returning to the heart from circulation and to pump blood out of the heart. The heart is a major structure of the cardiovascular system as it serves to drive blood to all the cells of the body. Blood is circulated along a pulmonary circuit and a systemic circuit. The pulmonary circuit involves the transport of blood between the heart and lungs, while the systemic circuit involves blood circulation between the heart and the rest of the body. Cardiac Cycle During the cardiac cycle (path of blood circulation in the heart), oxygen-depleted blood entering the right atrium from the venae cavae is moved along to the right ventricle. From there, blood is pumped out of the right ventricle to the main pulmonary artery and on to the left and right pulmonary arteries. These arteries send blood to the lungs. After picking up oxygen in the lungs, blood is returned to the left atrium of the heart via the pulmonary veins. From the left atrium, blood is pumped to the left ventricle and then out to the aorta. The aorta supplies blood for systemic circulation. Pulmonary Trunk and Pulmonary Arteries Superior view of the heart showing the major arteries and veins of the heart. MedicalRF.com/Getty Images The main pulmonary artery or pulmonary trunk is a part of the pulmonary circuit. It is a large artery and one of the three major blood vessels that extend from the heart. The other major vessels include the aorta and vena cavae. The pulmonary trunk is connected to the right ventricle of the heart and receives oxygen-poor blood. The pulmonary valve, located near the opening of the pulmonary trunk, prevents blood from flowing back into the right ventricle. Blood is conveyed from the pulmonary trunk to the left and right pulmonary arteries. Pulmonary Arteries The main pulmonary artery extends from the heart and branches into a right vessel and a left vessel. Right Pulmonary Artery (RPA): directs blood to the right lung. Extending from the pulmonary trunk, it dips under the aortic arch and behind the superior vena cava to the right lung. The RPA branches into smaller vessels within the lung.Left Pulmonary Artery (LPA): directs blood to the left lung. It is shorter than the RPA and is a direct extension of the pulmonary trunk. It connects to the left lung and branches into smaller vessels within the lung. The pulmonary arteries function to deliver blood to the lungs to acquire oxygen. In the process of respiration, oxygen diffuses across capillary vessels in lung alveoli and attach to red blood cells in the blood. The now oxygen-rich blood travels through lung capillaries to pulmonary veins. These veins empty into the left atrium of the heart.