What upsets the equilibrium of Starling's Law?

• A. Women
• B. Passive Hyperemia
• C. Active Hyperemia
• D. Both B and C

Answer: (D)

Starling's law describes how fluid moves across capillary walls based on a balance between capillary hydrostatic pressure (pushing fluid out) and oncotic pressure (pulling fluid in). This balance stays in check under normal conditions, but it can be upset when blood flow to a tissue changes.

In active hyperemia, arterioles dilate in response to increased tissue activity, boosting inflow to the capillaries. This raises capillary hydrostatic pressure, pushing more fluid into the interstitial space and tipping the balance toward filtration.

In passive hyperemia, venous obstruction raises the pressure on the venous side, which also increases capillary hydrostatic pressure. That again favors filtration into the tissue.

Both scenarios disrupt the equilibrium of Starling's forces, leading to excess interstitial fluid if drainage can't keep up. Women do not affect these fluid-exchange forces, so the correct idea is that both types of hyperemia upset the balance.