Editing Capillary (section)

=== Starling equation ===
[[File:2108 Capillary Exchange.jpg|thumb|upright=1.6|Diagram of the filtration and reabsorption in capillaries]]
The transport mechanisms can be further quantified by the [[Starling equation]].<ref name=nagy/> The Starling equation defines the forces across a semipermeable membrane and allows calculation of the net flux:

:<math>J_v = K_f [(P_c - P_i) - \sigma(\pi_c - \pi_i)],</math>

where:

: <math> (P_c - P_i) - \sigma(\pi_c - \pi_i) </math> is the net driving force,
: <math> K_f </math> is the proportionality constant, and
: <math> J_v </math> is the net fluid movement between compartments.

By convention, outward force is defined as positive, and inward force is defined as negative. The solution to the equation is known as the net filtration or net fluid movement (''J''<sub>''v''</sub>). If positive, fluid will tend to ''leave'' the capillary (filtration). If negative, fluid will tend to ''enter'' the capillary (absorption). This equation has a number of important physiologic implications, especially when pathologic processes grossly alter one or more of the variables.{{cn|date=January 2015}}

According to Starling's equation, the movement of fluid depends on six variables:
# Capillary [[hydrostatic pressure]] (''P''<sub>''c''</sub>)
# Interstitial hydrostatic pressure (''P''<sub>''i''</sub>)
# Capillary [[oncotic pressure]] ({{pi}}<sub>''c''</sub>)
# Interstitial oncotic pressure ({{pi}}<sub>''i''</sub>)
# Filtration coefficient (''K''<sub>''f''</sub>)
# Reflection coefficient (''σ'')