Vein function.

• A. Assist in lymphatic return by muscle contraction.
• B. Exchange gases with tissues.
• C. Carry oxygenated blood away from the heart.
• D. Carry deoxygenated blood to the heart.

Answer: (D)

Veins are vessels whose main job is to return blood to the heart. In the systemic circuit, the blood carried by veins is typically deoxygenated, having delivered oxygen to tissues and picked up carbon dioxide. So carrying deoxygenated blood toward the heart is their primary function. Gas exchange happens in the capillaries, not in veins, which is why a choice about exchanging gases with tissues isn’t correct. Arteries, not veins, carry blood away from the heart and toward tissues, while veins rely on valves and muscle movements to help return blood upward against gravity. An exception to this general rule is the pulmonary circuit, where the pulmonary veins carry oxygenated blood from the lungs to the heart, but the typical ve in the systemic view is returning deoxygenated blood to the heart.