At the venous end of a capillary the CHP is about 18 mm Hg while the BCOP holds at 25 mm Hg. What follows?

1. Capillary hydrostatic pressure falls along the capillary as fluid is lost, from about 35 mm Hg to about 18 mm Hg. 2. Blood colloidal osmotic pressure stays near 25 mm Hg, because plasma proteins cannot leave the vessel. 3. Net filtration pressure is 18 mm Hg minus 25 mm Hg, a negative 7 mm Hg. 4. A negative net filtration pressure means reabsorption, so water is drawn back into the capillary. 5. The balance point, where the two pressures are equal at 25 mm Hg and nothing moves on balance, sits near the middle of the capillary rather than at the venous end. 6. Reading the sign the wrong way gives filtration of 7 mm Hg, which reverses the direction of flow. 7. Adding the pressures gives 43 mm Hg and is arithmetically wrong as well as directionally wrong. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.3 Capillary Exchange_