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Biology Basics: Pulmonary Circulation

By Rene Fester Kratz

Pulmonary circulation, the first pathway of your two-circuit circulatory system, brings blood to your lungs for oxygenation. Following is a rundown of how blood moves during pulmonary circulation.

  1. Deoxygenated blood from your body enters the right atrium of your heart through the superior vena cava and the inferior vena cava.

    Superior means “higher,” and inferior means “lower,” so the superior vena cava is at the top of the right atrium, and the inferior vena cava is at the bottom of the right atrium.

  2. From the right atrium, the deoxygenated blood drains into the right ventricle through the right AV valve.

    When the ventricles contract, the right AV valve closes off the opening between the ventricle and the atrium so blood doesn’t flow back into the atrium.

  3. The right ventricle then contracts, forcing the deoxygenated blood through the pulmonary semilunar valve and into the pulmonary artery.

    The pulmonary semilunar valve keeps blood from flowing back into the right ventricle after it’s in the pulmonary artery.

  4. The pulmonary artery carries the blood that’s very low in oxygen to the lungs, where it becomes oxygenated.

  5. Freshly oxygenated blood returns from the lungs to the left atrium of the heart via the pulmonary veins.

    Note that your pulmonary veins are the only veins in your body that contain oxygenated blood; all your other veins contain deoxygenated blood. Likewise, your pulmonary arteries are the only arteries in your body that contain deoxygenated blood; all your other arteries carry oxygenated blood.

For questions 1–4, use the following terms to label the structures of the pulmonary pathway of your circulatory system in the figure.

a. Pulmonary artery

b. Pulmonary vein

c. Superior vena cava

d. Inferior vena cava

For question 5, use a colored pencil or highlighter to shade the pulmonary pathway of your circulatory system in the figure.

Pulmonary circulation and systemic circulation work together. [Credit: Illustration by Kathryn Born

Credit: Illustration by Kathryn Born, M.A.
Pulmonary circulation and systemic circulation work together.

The following are the answers to practice questions 1–5.

  1. c. Superior vena cava

  2. d. Inferior vena cava

  3. b. Pulmonary vein

  4. a. Pulmonary artery

  5. You should have shaded the upper loop in the figure from the heart to the lungs and back to the heart.