Related Experiment Video
Updated: Aug 1, 2026

Bedside Ultrasound for Guiding Fluid Removal in Patients with Pulmonary Edema: The Reverse-FALLS Protocol
Published on: July 28, 2018
Determinants of peritubular capillary fluid uptake in hydropenia and saline and plasma expansion
Abstract:
Hydrostatic (HPc) and oncotic (phic) pressures within the peritubular capillary, tubular pressure (Pt), nephron filtration rate, and plasma flow, and proximal fractional and absolute reabsorption (APR) were measured in anesthetized rats during hydropenia and plasma and saline expansion. Net interstitial pressure (phii-HPi) was estimated from subcapsular hydrostatic and oncotic pressures during saline expansion and these data were applied to a mathematical model of peritubular capillary fluid uptake to determine the profile of effective reabsorption pressure (ERP) with distance (x*) alongthe capillary and calculate the peritubular capillary permeability coefficient (LpAr). ERPX* = (PHIC MINUS HPC)X* MINUS (PHII MINUS HPi) and APR = ERPX*LpAr. During saline expansion phii minus HPi was -12.1 plus or minus 0.8 mmHg and ERP,3.8 mm. The LpAr was 0.07 nl/s per g KW per mmHg, and this value was applied to hypropenia and plasma expansion to determine ERP and phii minus HPi. The phiiminus HPi was +6.0 and +5.0 mmHg, respectively, and ERP was 4.1 and 3.5 mmHg. Efective reabsorptive pressure remained positive along x* in all states, and phii minus HPi correlated best changes in phic and poorly with changes in efferent plasma flow. The APR did not correlate with either calculated phii minus HPi or the transepithelial driving pressure, Pt + phii minus HPi.
Related Concept Videos
Capillary Exchange
Reabsorption and Secretion in the Loop of Henle
Formation of Dilute Urine
Filtrate Osmolarity in the PCT
Initially, as the filtrate passes through the proximal convoluted tubule (PCT), its...
Formation of Concentrated Urine
Fluid Movement Between Compartments
Physiology of the Genitourinary System II: Tubular Reabsorption and Secretion

