Final answer:
The veins have the lowest pressure among the blood vessels due to the distance the blood has traveled from the heart and the accompanying loss of the initial pressure, along with their structural features designed for low-pressure flow.
Step-by-step explanation:
The blood vessels with the lowest pressure are the veins. This low pressure comes about because, by the time blood has traveled through arterioles, capillaries, and venules, it has lost the high pressure initially imparted by the heart's contractions. Veins have thin walls, large lumens, and commonly feature valves that aid the movement of blood back to the heart. Their design allows for the accommodation of blood flow at low pressure, which is essential for preventing blood from pooling, especially in the extremities where the force of gravity can work against it.