bp31000 wrote:WangwithaTang wrote:Ok, so the general equation for starling's forces is just (all forms of hydrostatic pressure) - (all forms of oncotic pressure)?

no

[ Hydrostatic pressure of inside the capillary(pushes water out) + osmotic pressure of interstitium (pulls water out into interstitium) ] - [hydrostatic pressure in the interstitium (pushes water from coming into interstitium) + osmotic pressure in capillary (tries to pull water into capillary)]

This is my understanding of it. someone please correct me if i am wrong.

From my understanding, the general equation for Starling's forces is (Capillary hydrostatic - interstitial hydrostatic) - (Capillary oncotic - interstitial oncotic) in terms of variables. There are coefficients in the equation (filtration coefficient, reflection coefficient). There are versions of the equation with variables defined under google images.

Conceptually, hydrostatic pressure will move water out because there is more free water (greater water potential), while oncotic pressure will draw water to an area, due to a lower water potential, with water potential being the amount of free water unbound to solutes and water moving from areas of high to low potential. For example, higher hydrostatic pressure inside the capillaries will increase the water potential and move water out of the capillary IF the concentration of solutes in the interstitial fluid is greater. If the concentration of solutes inside the capillary is greater (aka a lower water potential and greater oncotic pressure) than the interstitium, then water will move into the capillary.

The Starling's forces equation refers specifically to the net flow of fluid between capillary and interstitial spaces. A positive net flux means that water is leaving the capillary (Hydrostatic>oncotic) while a negative flux indicates water entering (oncotic>hydrostatic). Hopefully, this explanation is helpful!