Final answer:
Reabsorption is when fluid and small solutes easily flow back into the blood from the capillaries, helped by the balance between capillary hydrostatic pressure and blood colloidal osmotic pressure.
Step-by-step explanation:
When fluid and small solutes flow easily through capillaries back into the blood, it is called reabsorption. This process primarily occurs near the venules due to the dynamic between the capillary hydrostatic pressure and the blood colloidal osmotic pressure. While proteins and large solutes are too big to pass through the capillary walls, the more watery plasma part of the blood can. Since the capillary hydrostatic pressure (18 mm Hg) is less than the blood colloidal osmotic pressure (25 mm Hg), fluid re-enters the capillary. Approximately 85% of the plasma that leaves the capillaries diffuses back in near the venules, promoting reabsorption. This fluid movement between compartments is a crucial aspect of the body's fluid regulation and nutrient delivery system.
The osmotic pressure, sometimes referred to as oncotic pressure, is the net pressure that drives reabsorption. It is determined by the osmotic concentration gradients, which are the difference in solute-to-water concentrations in the blood and tissue fluid. The lymphatic system helps to manage the remaining fluid by draining excess from interstitial spaces, filtering it through lymph nodes, and returning it to the bloodstream.