Capillary Filtration: The rate of filtration depends on balance of starling forces, the hydrostatic pressure gradient and osmotic pressure gradient. When the hydrostatic pressure gradient is more than the osmotic pressure gradient there is outward movement of fluid from the capillaries into the interstitium. Net filtration pressure = hydrostatic pressure gradient - osmotic pressure gradient If net filtration pressure (NFP) is positive then there is outward movement of fluid across the capillary and if negative net filtration pressure (NFP) then inward movement of fluid occurs. Ref: Ganong's Review of Medical Physiology, 21st Edition, Page 594