Final answer:
Fluid through the circulatory system is primarily moved by a pressure gradient resulting from the heart's pumping, as well as through osmotic gradients and bulk flow mechanisms involving hydrostatic and osmotic pressure.
Step-by-step explanation:
The kind of gradient used to move fluid through the circulatory system is primarily a pressure gradient created by the pumping action of the heart. However, fluid also moves between compartments along an osmotic gradient produced by the difference in concentration of solutes on either side of a semi-permeable membrane.
In addition, bulk flow involves two pressure-driven mechanisms in the mass movement of fluids through capillary beds: hydrostatic pressure and osmotic pressure. The rhythmic movement of smooth muscle and the action of skeletal muscles, as well as the presence of one-way valves in the veins, also contribute to the movement of blood against gravity.