Final answer:
Edema can result from incompetent venous valves or congestive heart failure, as increased pressure in the veins can promote the flow of fluids into the interstitial fluid.
Step-by-step explanation:
Edema, an abnormal increase in interstitial fluid, can result from incompetent venous valves or congestive heart failure. When blood accumulates in a vein, it increases the pressure within the vein, which can be reflected back into smaller veins, venules, and capillaries.
This increased pressure promotes the flow of fluids out of the capillaries and into the interstitial fluid, leading to edema.