Final answer:
Blood circulates through the body by being pumped from the heart into arteries, which branch into arterioles and capillaries for nutrient exchange, and is then returned to the heart through venules and veins, facilitated by valves to prevent backflow.
Step-by-step explanation:
Blood flow around the body is a continuous and regulated process involving several key structures: the heart, arteries, and veins. The heart is the pumping organ that pushes blood throughout the body. Blood enters the heart at the atria and then flows into the ventricles, which contract and send blood through the arteries. These arteries branch into arterioles and further into capillaries where gas and nutrient exchange occurs with body tissues.
The aorta is the main artery of the systemic circulation, branching into major arteries that supply different parts of the body. Arteries have strong but elastic walls to handle the pressure from the heartbeat. As the blood travels further away from the heart, arteries have more muscle to help regulate the flow rate of blood.
After passing through capillaries, blood is collected into small vessels called venules that join to form veins. Veins carry the blood back to the heart, and both arteries and veins are equipped with valves to prevent the backflow of blood and ensure a one-way circulation. This efficient system allows for the continuous delivery and return of blood, sustaining life by transporting oxygen and nutrients while removing waste products.