In terms of hydrostatic and oncotic pressures, how is GFR calculated?

The correct equation for calculating the Glomerular Filtration Rate (GFR) incorporates both hydrostatic and oncotic pressures acting across the glomerular capillaries. GFR is determined by the net filtration pressure, which is influenced by the hydrostatic pressure within the glomerular capillary (P GC) and the Bowman's space (P BS), as well as the oncotic pressures in the glomerular capillary (∏ GC) and in Bowman's space (∏ BS).

The equation reflects the balance of these pressures: hydrostatic pressures promote filtration, while oncotic pressures oppose it. Thus, GFR can be calculated as follows:

GFR = Kf [(P GC - P BS) - (∏ GC - ∏ BS)]

In this equation:

• Kf represents the filtration coefficient, a constant that reflects the permeability of the glomerular membrane and the surface area available for filtration.

• (P GC - P BS) captures the difference in hydrostatic pressures, with P GC promoting filtration and P BS resisting it.

• (∏ GC - ∏ BS) reflects the difference in oncotic pressures, with ∏ GC opposing filtration and ∏ BS promoting it (though ∏ BS