Chapter 20 - The Circulatory System: Blood Vessels and Circulation - Study Guide - Testing Your Comprehension - Page 801: 2

Net filtration or reabsorption pressure in a capillary is determined by the balance between hydrostatic pressure and colloid osmotic pressure (COP) gradients across the capillary walls. The formula to calculate net pressure is: Net Pressure = (Hydrostatic Pressure in Capillary - Hydrostatic Pressure in Interstitium) - (Colloid Osmotic Pressure in Capillary - Colloid Osmotic Pressure in Interstitium) Given the values you provided: Hydrostatic Pressure in Capillary (Pc) = 28 mm Hg Hydrostatic Pressure in Interstitium (Pi) = -2 mm Hg (negative because it's directed out of the capillary) Colloid Osmotic Pressure in Capillary (COPc) = 25 mm Hg Colloid Osmotic Pressure in Interstitium (COpi) = 4 mm Hg Substitute these values into the formula: Net Pressure = (28 mm Hg - (-2 mm Hg)) - (25 mm Hg - 4 mm Hg) Net Pressure = (30 mm Hg) - (21 mm Hg) Net Pressure = 9 mm Hg The net pressure is 9 mm Hg. Since the value is positive, the net pressure is directed out of the capillary, indicating a net filtration of fluid from the capillary into the interstitial space. This is a normal physiological process in capillaries, where filtration predominates at the arterial end due to the hydrostatic pressure gradient and is partially balanced by the colloid osmotic pressure gradient. At the venous end, reabsorption increases due to decreased hydrostatic pressure and increased colloid osmotic pressure.

Net filtration or reabsorption pressure in a capillary is determined by the balance between hydrostatic pressure and colloid osmotic pressure (COP) gradients across the capillary walls. The formula to calculate net pressure is: Net Pressure = (Hydrostatic Pressure in Capillary - Hydrostatic Pressure in Interstitium) - (Colloid Osmotic Pressure in Capillary - Colloid Osmotic Pressure in Interstitium) Given the values you provided: Hydrostatic Pressure in Capillary (Pc) = 28 mm Hg Hydrostatic Pressure in Interstitium (Pi) = -2 mm Hg (negative because it's directed out of the capillary) Colloid Osmotic Pressure in Capillary (COPc) = 25 mm Hg Colloid Osmotic Pressure in Interstitium (COpi) = 4 mm Hg Substitute these values into the formula: Net Pressure = (28 mm Hg - (-2 mm Hg)) - (25 mm Hg - 4 mm Hg) Net Pressure = (30 mm Hg) - (21 mm Hg) Net Pressure = 9 mm Hg The net pressure is 9 mm Hg. Since the value is positive, the net pressure is directed out of the capillary, indicating a net filtration of fluid from the capillary into the interstitial space. This is a normal physiological process in capillaries, where filtration predominates at the arterial end due to the hydrostatic pressure gradient and is partially balanced by the colloid osmotic pressure gradient. At the venous end, reabsorption increases due to decreased hydrostatic pressure and increased colloid osmotic pressure.