Flow Resistance along the Rat Renal Tubule.

Flow Resistance along the Rat Renal Tubule. Am J Physiol Renal Physiol. 2018 Aug 08;: Authors: Gilmer GG, Deshpande V, Chou CL, Knepper MA Abstract The Reynolds number in the renal tubule is extremely low, consistent with laminar flow. Consequently, luminal flow can be described by the Hagen-Poiseuille laminar flow equation. This equation calculates the volumetric flow rate from values of the axial pressure gradient and flow resistance, which is dependent on the length and diameter of each renal tubule segment. Our goal was to calculate the pressure drop along each segment of the renal tubule and determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known flow rates, tubule lengths, and diameters for each renal tubule segment, it was found that maximum pressure drop occurred in two segments: the thin descending limbs of Henle and the inner medullary collecting ducts. The high resistance in the thin descending limbs is due to their small diameters. The steep pressure drop observed in the inner medullary collecting ducts is due to the convergent structure of the tubules, which channels flow into fewer and fewer tubules toward the papillary tip. For short-looped nephrons, the calculated glomerular capsular pressure matched measured values, even with the high collecting duct flow rates seen in water diuresis, providing that tubule compliance was taken into account. I...
Source: Am J Physiol Renal P... - Category: Urology & Nephrology Authors: Tags: Am J Physiol Renal Physiol Source Type: research