Final answer:
The correct answer to the question is a capillary, as it will have a lower concentration of formed elements at the vena cava end because of the fluid exchange in the capillary beds that leads to a relative concentration of formed elements in the venous system as blood returns to the heart.
Step-by-step explanation:
The question asks which type of blood vessel will have a lower concentration of formed elements at the vena cava end. Formed elements refer to the cellular components of blood, including red blood cells, white blood cells, and platelets. As blood moves through the circulatory system, it travels from arteries to arterioles, then to capillaries, and finally converges into venules, which lead to larger veins and eventually the vena cava.
In the arterial system, the blood is under high pressure and travels away from the heart, distributing oxygen and nutrients to the body. The arteries branch into smaller arterioles which lead to capillary beds where exchange with body tissues occurs. As blood flows out of the capillaries and into venules, the pressure has significantly diminished. The vein system, which includes the venules and veins, operates under much lower pressure, which is why the veins have valves that assist in the unidirectional flow of blood back to the heart.
Considering the nature of blood flow and the role of different blood vessels, the correct answer is that a capillary will have a lower concentration of formed elements at the vena cava end. This is because, by the time blood has passed through the extensive network of capillaries where exchange of substances takes place, some fluid portion of the blood has leaked into the interstitial space, leaving the formed elements more concentrated in the emerging venules that lead to the veins and finally to the vena cava.