Final answer:
In the cardiovascular system, veins are responsible for carrying blood back to the heart after it has circulated through the body, moving from capillaries to venules and then into larger veins.
Step-by-step explanation:
In the cardiovascular system, veins are responsible for carrying blood back to the heart after it has circulated through the body. This process begins in the capillary beds, which are the site of nutrient and waste exchange between the blood and body tissues. From the capillaries, the blood is collected into venules, which are small blood vessels that combine to form larger veins. The largest vein is the inferior vena cava, which carries deoxygenated blood from the lower body, and the superior vena cava carries deoxygenated blood from the upper body, with both returning the blood to the heart.
The primary function of arteries is to carry blood away from the heart. They branch into smaller arterioles and even smaller capillaries. Capillaries deliver oxygen and nutrients to the body tissues and collect carbon dioxide and wastes. After reaching the capillaries, the blood then moves into venules, and then into veins that transport it back to the heart. Unlike arteries, veins contain valves to prevent backflow and move blood by the squeezing action of muscles, rather than primarily by the heartbeat's pressure.