It's All In The Lungs



Pulmonary circulation is the movement of blood from the heart, to the lungs, and back to the heart
again. This is just one phase of the overall circulatory system.

The veins bring waste-rich blood back to the heart, entering the right atrium throughout two large
veins called vena cavae. The right atrium fills with the waste-rich blood and then contracts, pushing
the blood through a one-way valve into the right ventricle. The right ventricle fills and then contracts,
pushing the blood into the pulmonary artery which leads to the lungs. In the lung capillaries, the
exchange of carbon dioxide and oxygen takes place. The fresh, oxygen-rich blood enters the
pulmonary veins and then returns to the heart, re-entering through the left atrium. The oxygen-rich
blood then passes through a one-way valve into the left ventricle where it will exit the heart through
the main artery, called the aorta. The left ventricle's contraction forces the blood into the aorta and
the blood begins its journey throughout the body.

The one-way valves are important for preventing any backward flow of blood. The circulatory
system is a network of one-way streets. If blood started flowing the wrong way, the blood gases
(oxygen and carbon dioxide) might mix, causing a serious threat to your body.

You can use a stethoscope to hear pulmonary circulation. The two sounds you hear, "lub" and "dub,"
are the ventricles contracting and the valves closing.