Answer
Blood pressure and osmotic pressure are the two forces exchanging materials across the walls of a capillary. Blood pressure pushes fluids toward tissues, and osmotic pressure pushes water out of the tissues.
Blood pressure is higher than osmotic pressure at the arterial (front) end of the capillary, and osmotic pressure is higher than blood pressure at the venous (back) end of the capillary.
Midway along the capillary, the two forces cancel each other out, and the fluids stop moving. At this point, solutes in the fluid flow according to their concentration gradient. Oxygen and nutrients flow out of the capillaries, and carbon dioxide and waste flow into the capillaries.
Work Step by Step
Blood pressure and osmotic pressure are the two forces exchanging materials across the walls of a capillary. Blood pressure pushes fluids toward tissues, and osmotic pressure pushes water out of the tissues.
Blood pressure is higher than osmotic pressure at the arterial (front) end of the capillary, and osmotic pressure is higher than blood pressure at the venous (back) end of the capillary.
Midway along the capillary, the two forces cancel each other out, and the fluids stop moving. At this point, solutes in the fluid flow according to their concentration gradient. Oxygen and nutrients flow out of the capillaries, and carbon dioxide and waste flow into the capillaries.
