Which of the following are included in the four main Starling forces?

The correct answer highlights the significance of oncotic pressure outside the capillary wall as one of the four main Starling forces, which govern the movement of fluid across capillary membranes.

Starling forces are essential in determining the net movement of fluids between the intravascular and extravascular compartments, which involves hydrostatic pressure and oncotic pressure. Specifically, these forces include:

1. Capillary hydrostatic pressure: This is the blood pressure within the capillaries, promoting the movement of fluid out of the capillaries.

2. Interstitial hydrostatic pressure: The pressure exerted by the fluid in the interstitial space, influencing fluid movement back into the capillaries.

3. Capillary oncotic pressure (or colloid osmotic pressure): This refers to the osmotic pressure generated by proteins (mainly albumin) in the blood, pulling water into the capillaries.

4. Interstitial oncotic pressure: The osmotic pressure from proteins in the interstitial fluid, which can draw fluid out of the capillaries.

Option A, emphasizing the oncotic pressure outside the capillary wall, is crucial as it acknowledges the role of the interstitial oncotic pressure in fluid dynamics. This helps balance