several pressure involved in forcing fluid across capillary wall from inside to the ecf and forces that work in reverse that draw fluid from ecf into capillary bed. First pressure is the hydrostatic pressure (blood pressure in blood vessels) and the other is the oncotic pressure. Two hydrostatic pressure important in regulating the direction of fluid movement: cap (within the capillary, isf (pressure within the interstitial fluid) Isf: small hydrostatic pressure of ~1 mmhg: occurs in the ecf in general (doesn"t matter where in the circulatory system). pressure in blood vessel will change as we go from artery to venous side: because capillary bed resist flow, pressure will drop from arterial side of capillary bed to the venous side. arterial to capillary bed: 38 mmhg in arterioles in the beginning of capillary as the bed is beginning to form.