Day 2: The Heart of the Matter

The Heart as a Pump

Blood is pumped through the heart in the following manner:

Pulmonary Side of the Heart:

1. Blood (low in oxygen and high in carbon dioxide) enters the right atrium from the superior and inferior vena cava. The superior vena cava is the large vein that returns blood to the heart from the upper half of the body and the inferior vena cava is the large vein that returns blood to the heart from the lower half of the body.

2. At this point the tricuspid valve, the valve separating the right atrium from the right ventricle, is open and blood begins to fill the right ventricle. The right atrium contracts to force the rest of the blood into the right ventricle.

3. When the right ventricle is full and begins to contract, the tricuspid valve is forced shut. (lub)

4. The right ventricle contracts and pumps the blood through the pulmonary artery to the lungs. When the right ventricle relaxes, the blood in the pulmonary artery forces the pulmonary valve shut. (dub)

In the lungs, the blood from the body trades its carbon dioxide for oxygen.

Systemic Side of the Heart:

1. Now rich in oxygen, the blood returns from the lungs to the left atrium of the heart via the pulmonary veins.

2. The oxygen rich blood fills the left ventricle. The left atrium contracts to force the rest of the blood into the left ventricle.

3. When the left ventricle is full and begins to contract, the bicuspid valve is forced shut. (lub)

4. The left ventricle contracts and pumps the blood through the aortic valve into the aorta. The aorta is the main artery supplying oxygen-rich blood to the body. When the left ventricle relaxes, the blood in the aorta forces the aortic valve shut. (dub)

The right and left atria contract at the same time. The tricuspid and bicuspid valves shut at the same time creating the "lub" sound. The right and left ventricles contract at the same time. And the pulmonary and aortic valves shut at the same time creating the "dub" sound.

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