Final answer:
The opposing forces that govern net filtration and absorption across the capillary are termed the starling forces. These are made up of hydrostatic pressure, which pushes fluid out of capillaries, and osmotic pressure.
Step-by-step explanation:
The opposing forces that govern net filtration and absorption across the capillary are collectively termed the starling forces. These include hydrostatic pressure and osmotic pressure, which work in opposite directions to regulate the movement of fluid. Hydrostatic pressure, such as capillary hydrostatic pressure (CHP) and interstitial fluid hydrostatic pressure (IFHP), typically forces fluid out of the capillaries into the interstitial space. Conversely, osmotic pressure, often referred to as oncotic pressure, pulls fluid back into the capillaries from the interstitial fluid, predominantly through the osmotic concentration gradients and the blood colloidal osmotic pressure (BCOP).
At the arterial end of the capillary, net filtration occurs because CHP is greater than BCOP. Near the midpoint, there is no net movement since CHP equals BCOP, and at the venous end, net reabsorption occurs since BCOP is higher than CHP. The net filtration pressure (NFP) is the difference between these pressures and dictates the direction of the fluid movement. Net filtration pressure will be positive when fluid is being pushed out of the capillary (filtration), and negative when fluid is being absorbed into the capillary (reabsorption).