The aorta is the human body's single largest blood vessel. The aorta is the largest single blood vessel in the body. It is around the diameter of your thumb. The aorta carries oxygen-rich blood to the various parts of the body from the left ventricle. The pulmonary artery on the other hand is the vessel that transports de-oxygenated blood to the lungs from the right ventricle. One of the most common misconceptions is that arteries only carry oxygen rich blood. A classification of arteries as vessels that take blood away from the heart would be more appropriate. Like the walls of the vena cava, those of the pulmonary artery have much greater void spaces, which are meant for albumin, as compared to those of systemic arteries like the aorta.
The pulmonary artery leaves the right ventricle and facilitates transport of blood to the lungs. The aorta leaves the left ventricle and facilitates transport of blood to the rest of the body.