Lesson 1, Topic 1
In Progress

Starling Forces

 What is the role of Starling forces?

Starling forces are the “forces” that are involved with the movement of fluid across the permeable membranes of the capillary beds. Within the capillary, the capillary hydrostatic pressure “forces” fluid out of the capillary and into the interstitium; the interstitial hydrostatic pressure “forces” fluid to leave the interstitium and enter the capillary; the capillary plasma colloid osmotic pressure (also called plasma oncotic pressure) “draws” fluid into the capillary; and the interstitial fluid colloid osmotic pressure (also called oncotic pressure) “draws” fluid into the interstitium. The net movement of fluid across the capillary membrane is affected by both the magnitude of the imbalance between the hydrostatic and osmotic forces and the permeability of the capillary membrane to water. Kf is known as the permeability coefficient.

Thus the net movement of water across the capillary membrane can be expressed via the equation:

Kf[(HPc-HPif)-(COPc-COPif)]

HPc = Hydrostatic pressure in the capillary
HPif = Hydrostatic pressure of the interstitial fluid
COPc = Colloidal osmotic pressure of the capillary plasma
COPif = Colloidal osmotic pressure of the interstitial fluid