Final answer:
The smallest divisions into which arteries branch before connecting to veins are called B. capillaries, where the exchange of substances occurs between blood and cells.
Step-by-step explanation:
The aorta branches into smaller divisions called arteries, which in turn branch into smaller divisions called capillaries. The arteries leading away from the heart branch into smaller vessels called arterioles, which then lead to the capillary beds. Capillaries are the smallest type of blood vessels where the exchange of gases and other substances occurs between the blood and the cells. After capillaries, the blood collects into venules which lead back to larger veins, completing the return circuit to the heart.
The aorta branches into smaller arteries, which further divide into arterioles. Arterioles are the smallest arteries in the cardiovascular system and play a crucial role in regulating blood flow and blood pressure. These arterioles eventually lead to capillaries, which are the smallest blood vessels where the exchange of gases and other substances occurs between the blood and the surrounding tissues.