Questions: Circulatory System: Heart, Blood, and Vessels

Question 1

Why does the heart need to pump blood to the lungs before sending it to the rest of the body?

• A. To warm the blood up before it circulates
• B. To filter out germs before they reach other organs
• C. To pick up oxygen and drop off carbon dioxide
• D. To add more blood cells before circulation

Answer: (C)

Blood returning from the body has delivered its oxygen to cells and picked up carbon dioxide waste. Before it can be useful again, it needs to go to the lungs to dump the carbon dioxide (which you exhale) and pick up a fresh supply of oxygen (which you inhale). This is pulmonary circulation -- the loop between the heart and lungs.

Question 2

Blood inside your veins is blue, which is why veins look blue through your skin.

• T. True
• F. False

Answer: False

Blood is never blue. Oxygen-rich blood is bright red, and oxygen-poor blood is dark red (sometimes described as maroon or crimson). Veins appear blue or green through the skin because of how light at different wavelengths penetrates skin and reflects back to your eyes. It's an optical effect of the tissue over the veins, not the color of the blood itself.

Question 3

Explain the difference between arteries and veins in terms of which direction they carry blood relative to the heart.

Model answer: Arteries carry blood away from the heart to the body's tissues. Veins carry blood back toward the heart from the tissues. This is true regardless of whether the blood is oxygenated or not -- the defining feature is direction of flow, not oxygen content.

The directional definition is the correct and reliable one. While it's tempting to define arteries as 'oxygen-rich' and veins as 'oxygen-poor,' the pulmonary vessels break that pattern: the pulmonary artery carries deoxygenated blood away from the heart to the lungs, and the pulmonary vein carries oxygenated blood back. Direction relative to the heart is what actually defines arteries vs. veins.