WAEC - Biology (2015 - No. 8)

Blood pressure is higher in arteries than in veins because arteries directly receive blood pumped from the heart under high pressure, and their thick, elastic walls are designed to accommodate this pressure. Because the space in the arteries is narrower, the same amount of blood passing through them increases the blood pressure. Veins can constrict to reduce their capacity to hold blood, forcing more blood into the arteries. As a result, blood pressure increases.

In summary, contraction and relaxation are responsible for the high blood pressure in arteries.