Which term describes the circulation between the heart and lungs for gas exchange?

• A. Lymph nodes
• B. Pulmonary circulation
• C. Hemoglobin
• D. Systemic circulation

Answer: (B)

The main idea here is the separate loop that specifically carries blood between the heart and the lungs for gas exchange. In this pathway, deoxygenated blood is driven from the right side of the heart to the lungs via the pulmonary arteries. There, gas exchange occurs across the alveolar capillaries: oxygen enters the blood and carbon dioxide exits. The now-oxygenated blood returns to the heart through the pulmonary veins and enters the left atrium, from which it can be pumped to the body again. This pulmonary circulation is distinct from systemic circulation, which sends blood from the left heart to the rest of the body to deliver oxygen and nutrients and to remove wastes. Lymph nodes belong to the immune/lymphatic system, not a blood circulation, and hemoglobin is the oxygen-carrying protein inside red blood cells, not a circulation pathway.