Edema develops when which of the following changes in Starling forces occur?

• A. Decreased capillary hydrostatic pressure leads to edema.
• B. Increased plasma oncotic pressure alone causes edema.
• C. Increased capillary hydrostatic pressure, increased capillary permeability, or decreased plasma oncotic pressure can cause edema.
• D. Decreased capillary permeability prevents edema.

Answer: (C)

Edema happens when more fluid leaves the capillaries and accumulates in the interstitial space than is drawn back in. This depends on Starling forces: capillary hydrostatic pressure pushes fluid out, while plasma oncotic pressure pulls fluid in; changes in these forces, or in capillary permeability, can tip the balance toward swelling.

The best choice says edema can arise from several situations: higher capillary hydrostatic pressure pushes more fluid out; higher capillary permeability lets more fluid and proteins escape; or lower plasma oncotic pressure reduces the inward pull of fluid into the vessels. All of these shifts increase net filtration or decrease reabsorption, leading to edema.

Decreased capillary hydrostatic pressure would actually reduce filtration and edema. Increased plasma oncotic pressure would pull more fluid back into the vessels, counteracting edema rather than causing it. Decreased capillary permeability would limit fluid loss from the capillaries, making edema less likely. So the combination of increased outward force, increased leakage, or reduced inward force best explains edema formation.