Final answer:
Reabsorption is the movement of fluid by bulk in the opposite direction of filtration, crucial in the circulatory system and particularly within the kidneys, driven primarily by osmotic pressure.
Step-by-step explanation:
The movement of fluid by bulk that is in the opposite direction of filtration is known as reabsorption. In the human body, this process is crucial in the circulatory system, particularly within the kidneys. Bulk flow, which involves moving fluid in a blood vessel from an area of higher hydrostatic pressure to an area of lower pressure through filtration, is met with the inverse process—reabsorption—where fluid moves from the surrounding tissues back into the capillaries, primarily driven by osmotic pressure differences. While filtration is driven by hydrostatic pressure, pushing fluid and solutes out of the capillaries, reabsorption primarily relies on osmotic pressure to draw fluid back into the vascular system.