Glomerular Filtration Rate (GFR)

If we disregard any oncotic pressure in the Bowman's capsule, we have in effect, three pressures to consider: glomerular hydrostatic pressure, glomerular oncotic pressure, and Bowman's capsule hydrostatic pressure. These can be expressed as a formula that will tell us the amount of hydrostatic pressure pushing fluid out of the glomerulus:

Net glomerular pressure equals: Glomerular hydrostatic pressure minus [glomerular oncotic pressure + Bowman's capsule hydrostatic pressure]

In order to measure the glomerular filtration rate, we must add to this measurement an estimation of glomerular permeability, and surface area – that is, how many functioning nephrons are available in the body for filtration, and how effectively the glomeruli filter fluid. A normal glomerular filtration rate is around 125mls/min, and this measurement is used to determine, and to classify, kidney function.