The primary function of veins is to:

• A. Carry deoxygenated blood from tissues and return it to the heart.
• B. Oxygenate tissues
• C. Drain lymph
• D. Propel blood through arterial network

Answer: (A)

Veins are the vessels that bring blood back to the heart. After tissues extract oxygen and nutrients, the blood becomes lower in oxygen and higher in carbon dioxide. This deoxygenated blood is collected into small veins and venules, then travels through progressively larger veins until it returns to the heart to be re-oxygenated in the lungs and re-pumped to the body. Veins operate under lower pressure than arteries and have valves to prevent backflow, and they also serve as a major reservoir that holds most of the blood volume. The main idea is that the job of veins is to return blood to the heart, completing the circulatory circuit. An important note: in the lungs, blood is oxygenated and returns to the heart via the pulmonary veins, but in the systemic circulation the primary task of veins is to carry deoxygenated blood back to the heart.