Every day we breathe in and out, and most of the time we don't even think about it. We breathe air in through our nose, it goes through our windpipe (the trachea), and then into our lungs. What happens after the air gets into the lungs? How is it related to our heartbeat? An understanding of pulmonary circulation will answer these questions.
The word pulmonary comes from the Latin word for lungs, and circulation describes something moving in a circle. The path blood takes between the heart and the lungs is called the pulmonary circulation system.
We need oxygen in all parts of our body for our cells to function. Oxygen helps the cells produce energy. The lungs and the heart work together to get oxygen to the cells. Carbon dioxide is the waste product released by the cells into the blood. After it delivers oxygen to the cells, blood brings carbon dioxide back to the heart so the carbon dioxide can be replaced by fresh oxygen.
We breathe air into our lungs. At the same time, blood filled with waste carbon dioxide comes through capillaries into the lungs. When we breathe in, the blood in the capillaries absorbs oxygen from the air, and when we breathe out we get rid of the carbon dioxide.
Here is a list describing the steps in the circulation systems. Blood goes through the pulmonary circulation system to the systemic circulation system in a continuous path.
The pulmonary circulation system works as follows:
1. Blood containing mostly carbon dioxide leaves the right side of the heart.
2. The blood goes through the pulmonary artery to the lungs.
3. The blood picks up oxygen in the lungs from the air we breathe in.
4. The blood leaves behind carbon dioxide which we breathe out.
5. The blood returns to the heart through the pulmonary veins.
After that the blood goes through the body in the systemic circulation system. It delivers oxygen to the cells of the body and then returns to the heart and the whole thing starts over again.
It took a very long time for scientists to understand this process. Galen, a Greek physician, lived between the years 130 and 201. He was the first scientist to state that blood, and not air, flowed through the circulatory system. 1,300 years later, in 1628, William Harvey proved blood flows through the body in a well defined route. The discovery of oxygen came after Harvey died, but his explanation of pulmonary circulation was correct.