Final answer:
Hydrostatic pressure drives plasma and nutrients out of the capillaries at their arterial ends, while osmotic pressure allows for reabsorption at the venous ends. More fluid exits than returns due to pressure differences, with the lymphatic system being crucial for returning the excess fluid to the circulatory system, ensuring tissue health and circulatory volume maintenance.
Step-by-step explanation:
Pressure differences play a critical role in the movement of substances into and out of the capillaries. The hydrostatic pressure, which is the force exerted by blood against the walls of the blood vessels, pushes plasma and nutrients from the arterial end of the capillaries into the surrounding tissues due to being higher than the colloid osmotic pressure. Conversely, at the venous end, the hydrostatic pressure is lower, allowing fluid and cellular wastes to enter the capillaries driven by the higher osmotic pressure from the accumulated solutes within the blood vessels.
More fluid leaves the capillaries than is returned because the hydrostatic pressure at the arterial end is generally higher than the osmotic pressure. The net movement favors water and solutes being pushed into the interstitial fluid. This lost fluid is recovered by the lymphatic system, which drains the surplus interstitial fluid and returns it to the vasculature at the subclavian veins. This process is essential to prevent excessive fluid accumulation in tissues that could lead to swelling, and to maintain the volume of blood within the circulatory system.