The basic pattern of blood flow from the lungs to the rest of the body is:
1. Oxygen-rich blood from the lungs enters the left atrium of the heart through the pulmonary veins.
2. The left atrium contracts, pushing the blood into the left ventricle.
3. The left ventricle contracts, pumping the oxygen-rich blood out of the heart and into the aorta, the largest artery in the body.
4. The aorta branches into numerous smaller arteries that carry the oxygen-rich blood to all the organs and tissues of the body.
5. Within the organs and tissues, the arteries branch into smaller arterioles and eventually into tiny capillaries.
6. Capillaries allow for the exchange of nutrients, oxygen, and waste products between the blood and the surrounding tissues.
7. Oxygen and nutrients are delivered to the tissues, while waste products, such as carbon dioxide, are picked up by the blood.
8. Oxygen-poor blood, now carrying waste products, flows from the capillaries into venules.
9. Venules merge together to form larger veins.
10. Veins eventually converge into the superior and inferior vena cavae, which return the oxygen-poor blood to the right atrium of the heart.
11. The right atrium contracts, pushing the blood into the right ventricle.
12. The right ventricle contracts, pumping the oxygen-poor blood into the pulmonary artery.
13. The pulmonary artery carries the blood back to the lungs, where it picks up oxygen and releases carbon dioxide through the process of respiration.
14. The oxygen-rich blood from the lungs then restarts the cycle by entering the left atrium of the heart.