Which statement differentiates arteries from veins regarding direction of blood flow and oxygen content?

Which statement differentiates arteries from veins regarding direction of blood flow and oxygen content?

• A. Veins carry blood away from the heart (usually deoxygenated); arteries toward the heart (usually oxygenated).
• B. Arteries carry blood away from the heart (usually oxygenated; pulmonary exception); veins carry blood toward the heart (usually deoxygenated; pulmonary exception).
• C. Arteries carry blood toward the heart; veins away.
• D. Arteries and veins both carry blood in either direction.

Answer: (B)

Direction of blood flow relative to the heart and the typical oxygen content of the blood are the key ideas. In the systemic circulation, arteries carry blood away from the heart and usually carry oxygenated blood to tissues, while veins return blood toward the heart and usually carry deoxygenated blood back to the heart. The pulmonary circulation reverses this pattern: the pulmonary artery carries deoxygenated blood away from the heart to the lungs, and the pulmonary veins return oxygenated blood from the lungs to the heart. So the statement that best captures these patterns—arteries carrying blood away from the heart and usually oxygenated, with the pulmonary exception, and veins carrying blood toward the heart and usually deoxygenated, with the pulmonary exception—is the correct one. The other descriptions either reverse the direction, or misstate the typical oxygen content for systemic vessels, and they don’t account for the pulmonary exceptions.

Direction of blood flow relative to the heart and the typical oxygen content of the blood are the key ideas. In the systemic circulation, arteries carry blood away from the heart and usually carry oxygenated blood to tissues, while veins return blood toward the heart and usually carry deoxygenated blood back to the heart. The pulmonary circulation reverses this pattern: the pulmonary artery carries deoxygenated blood away from the heart to the lungs, and the pulmonary veins return oxygenated blood from the lungs to the heart.

So the statement that best captures these patterns—arteries carrying blood away from the heart and usually oxygenated, with the pulmonary exception, and veins carrying blood toward the heart and usually deoxygenated, with the pulmonary exception—is the correct one. The other descriptions either reverse the direction, or misstate the typical oxygen content for systemic vessels, and they don’t account for the pulmonary exceptions.