# 腎臟血流量(Renal blood flow, RBF)

（腎動脈壓力-腎靜脈壓力）/總腎血管阻力，以下推導

Renal plasma flow is the volume of plasma that reaches the kidneys per unit time. Renal plasma flow is given by the Fick principle:
$RPF = \frac{U_x V}{P_a - P_v}$
This is essentially a conservation of mass equation which balances the renal inputs (the renal artery) and the renal outputs (the renal vein and ureter). Put simply, a non-metabolizable solute entering the kidney via the renal artery has two points of exit, the renal vein and the ureter. The mass entering through the artery per unit time must equal the mass exiting through the vein and ureter per unit time:
$RPF_a \times P_a = RPF_v \times P_v + U_x \times V$
where Pa is the arterial plasma concentration of the substance, Pv is its venous plasma concentration, Ux is its urine concentration, and V is the urine flow rate. The product of flow and concentration gives mass per unit time.
As mentioned previously, the difference between arterial and venous blood flow is negligible, so RPFa is assumed to be equal to RPFv, thus
$RPF \times P_a = RPF \times P_v + U_x V$
Rearranging yields the previous equation for RPF:
$RPF = \frac{U_x V}{P_a - P_v}$

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