In human anatomy, there are a total of four pulmonary veins, and all of them connect to the left atrium of the heart. The heart pumps deoxygenated blood into the lungs via the pulmonary arteries. Once the blood has been oxygenated, it returns to the heart via the pulmonary veins. Then, the heart circulates this newly oxygenated blood throughout the body. The left pulmonary veins connect with the left lung, and the lungs themselves are filled with hollow air sacs called alveoli. This is where oxygen is removed from inhaled air. This also works as a gas exchange. Oxygen enters the blood while carbon dioxide leaves the blood stream. This carbon dioxide is then exhaled. To some, the terms "left pulmonary veins" may be a little misleading. Elsewhere in the body, veins transit deoxygenated blood, while arteries carry oxygenated blood. However, in the heart, this process is reversed. To this end, oxygen content is misleading. After all, veins carry blood to the heart, while arteries carry it away.