Final answer:
The correct answer is A. net filtration pressure, which describes the balance of hydrostatic pressure of the blood in the capillaries against the hydrostatic pressure of the tissue interstitial fluid.
Step-by-step explanation:
The term that is equal to the hydrostatic pressure of the blood in the capillaries minus the hydrostatic pressure of tissue interstitial fluid outside the capillaries is net filtration pressure (NFP). The NFP plays a pivotal role in managing the movement of fluid between the capillaries and the interstitial fluid surrounding them. Fluid exit from capillaries, also known as filtration, is primarily driven by the capillary hydrostatic pressure (CHP), which is usually higher than the interstitial fluid hydrostatic pressure (IFHP). On the contrary, fluid reabsorption into capillaries is influenced by osmotic pressure, largely generated by the solute concentrations in the blood versus the tissue fluid.
Put simply, NFP is the force driving fluid out of the capillary, which is calculated by subtracting the blood colloidal osmotic pressure (BCOP) from the CHP. This interaction reflects the balance of the hydrostatic and osmotic pressures, determining the direction and rate at which fluids move in and out of the vascular system. Importantly, the lymphatic system assists in maintaining fluid balance by draining excess fluid from the tissues.