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Inulin-containing foods can be rather gassy, especially for those unaccustomed to inulin and these foods should be consumed in moderation at first. [citation needed] Inulin is a soluble fiber, one of three types of dietary fiber including soluble, insoluble and resistant starch. Soluble fiber dissolves in water to form a gelatinous material.
Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function. [citation needed]PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAH from the blood reflects total renal plasma flow.
PAH is useful for the measurement of renal plasma flow. [1]The renal extraction ratio of PAH in a normal individual is approximately 0.92. [2] This means that unlike inulin and creatinine, which are filtered in the glomerulus and ignored by the rest of the kidney, aminohippuric acid is both filtered and secreted, being almost entirely removed from the bloodstream in a normal kidney.
Effective renal plasma flow (eRPF) is a measure used in renal physiology [1] to calculate renal plasma flow (RPF) and hence estimate renal function.. Because the extraction ratio of PAH is high, it has become commonplace to estimate the RPF by dividing the amount of PAH in the urine by the plasma PAH level, ignoring the level in renal venous blood.
The GFR can be determined by injecting inulin or the inulin-analog sinistrin into the blood stream. Since both inulin and sinistrin are neither reabsorbed nor secreted by the kidney after glomerular filtration, their rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter.
PAH is not reabsorbed and is secreted, so excretion = filtration + secretion. As with glucose, the transfer is at the proximal tubule, but in the opposite direction: from the peritubular capillaries to the lumen. At low levels, all the PAH is transferred, but at high levels, the transport maximum is reached, and the PAH takes longer to clear.
Inulin clearance is less commonly used to precisely determine glomerular filtration rate. Note - the above equation is valid only for the steady-state condition. If the substance being cleared is not at a constant plasma concentration (i.e. not at steady-state) K must be obtained from the (full) solution of the differential equation .
Renal plasma flow is the volume of plasma that reaches the kidneys per unit time. Renal plasma flow is given by the Fick principle: = 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).