Which statement about edema and Starling forces is true?

• A. Edema occurs only due to lymphatic obstruction.
• B. Edema results from decreased capillary permeability.
• C. Edema is caused exclusively by decreased hydrostatic pressure.
• D. Edema develops when capillary hydrostatic pressure increases, or oncotic pressure decreases, or capillary permeability increases.

Answer: (D)

Edema happens when the forces that move fluid across capillary walls shift toward more fluid leaving the capillaries than returning. This balance is described by Starling forces, mainly capillary hydrostatic pressure pushing fluid out, and plasma oncotic pressure pulling fluid back in, with capillary permeability shaping how easily fluid and proteins leak out.

If capillary hydrostatic pressure goes up, more fluid is forced into the interstitial space, leading to edema. If plasma oncotic pressure falls (less pulling power from proteins like albumin), fluid isn’t drawn back into the bloodstream as effectively, causing accumulation in tissues. If capillary permeability increases (as in inflammation or injury), more fluid—and proteins—escape into the interstitial space, promoting edema. These are all ways the balance can tip toward edema.

Other choices aren’t as accurate: decreased hydrostatic pressure would reduce fluid filtration rather than promote edema, and decreased capillary permeability would limit leakage. While lymphatic obstruction can also cause edema, the described mechanisms above cover the principal ways edema develops via Starling forces.