What is Pulmonary Circulation?
Pulmonary circulation is the short loop that carries deoxygenated blood from the right side of the heart to the lungs for gas exchange, then returns oxygenated blood to the left atrium. It's a low-pressure circuit distinct from systemic circulation.
Pulmonary circulation moves blood from the right ventricle through the pulmonary arteries to the lungs, where it picks up oxygen and releases carbon dioxide, then returns via the pulmonary veins to the left atrium.
- 1.Right ventricle — Pumps deoxygenated blood into the pulmonary trunk
- 2.Pulmonary arteries — Carry deoxygenated blood to the lungs — the only arteries carrying low-oxygen blood
- 3.Pulmonary capillaries — Gas exchange: CO2 released, O2 picked up in the alveoli
- 4.Pulmonary veins — Carry oxygenated blood back to the heart — the only veins carrying high-oxygen blood
- 5.Left atrium — Receives oxygenated blood, ready to enter systemic circulation
Step-by-step worked examples
Pulmonary artery pressure is about 25/8 mmHg, much lower than the aorta's 120/80 mmHg. Why is pulmonary pressure so low?
The right ventricle only needs to pump blood a short distance to the nearby lungs Low pressure protects the thin-walled pulmonary capillaries from fluid leaking into the alveoli High pulmonary pressure would cause pulmonary edema
Blood entering the lungs has an oxygen saturation of about 75%; blood leaving has about 98%. What caused the increase?
Deoxygenated blood arrives via the pulmonary arteries at about 75% saturation In the alveolar capillaries, O2 diffuses from air into blood and CO2 diffuses out Oxygen-rich blood leaves at about 98% saturation via the pulmonary veins
A pulmonary embolism blocks a branch of the pulmonary artery. What immediate effect does this have on gas exchange?
The blocked pulmonary artery branch can't deliver blood to that lung region Alveoli in that region are ventilated but not perfused, creating dead space Gas exchange in that area drops, and overall blood oxygenation can fall
Flashcards
Quick quiz
Q1.Pulmonary circulation begins in which heart chamber?
Q2.What is unusual about the pulmonary arteries compared to other arteries?
Q3.Where does gas exchange occur in pulmonary circulation?
Q4.After the lungs, oxygenated blood returns to the heart via the:
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Common mistakes
All arteries carry oxygenated blood. — Correct: Pulmonary arteries carry deoxygenated blood — artery and vein naming is based on direction, not oxygen content.
Pulmonary circulation and systemic circulation are the same loop. — Correct: They are two separate circuits, both starting and ending at the heart.
Pulmonary circulation is a high-pressure system like systemic circulation. — Correct: Pulmonary circulation is a low-pressure system (about 25/8 mmHg) that protects the delicate alveolar capillaries.
Gas exchange happens in the pulmonary arteries. — Correct: Gas exchange happens in the pulmonary capillaries around the alveoli, not in the arteries.
FAQ
What is pulmonary circulation?
The pathway that carries blood from the right ventricle to the lungs for gas exchange and back to the left atrium.
What is the pulmonary circulation pathway in order?
Right ventricle → pulmonary trunk → pulmonary arteries → lung capillaries → pulmonary veins → left atrium.
What are examples of pulmonary circulation disorders?
Pulmonary embolism, pulmonary hypertension, and pulmonary edema are common examples.
How is pulmonary circulation different from systemic circulation?
Pulmonary circulation is a short, low-pressure loop to the lungs; systemic circulation is a long, high-pressure loop to the rest of the body.