Why does the blood flow through lungs?

The blood flows through the lungs for the purpose of gas exchange. The lungs are responsible for taking in oxygen from the air and releasing carbon dioxide, which is a waste product of cellular respiration. The oxygen that we breathe in diffuses across the thin walls of the alveoli (tiny air sacs in the lungs) into the capillaries, which are tiny blood vessels that surround the alveoli. The oxygen-rich blood is then pumped out to the rest of the body through the pulmonary artery. At the same time, the carbon dioxide that is produced by the cells in the body diffuses across the capillaries into the alveoli, and is exhaled when we breathe out.

This process of gas exchange is essential for maintaining homeostasis in the body. The oxygen that is taken in by the lungs is used to produce energy in the cells, while the carbon dioxide that is released is a waste product of this process. By exchanging these gases, the lungs help to maintain the proper levels of oxygen and carbon dioxide in the blood, which is critical for the overall health and functioning of the body.