PHYSL402 Lecture Notes - Lecture 20: Proximal Tubule, Tubular Fluid, Extracellular Fluid
7 Nov 2016
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Limit to rate at which solute can be transported transport maximum (can be saturated) Limit due to saturation of specific transport systems: solute delivered in the tubule (tubular. Load) exceeds capacity of the carrier proteins and enzymes required. Note: some actively transported substances are passively reabsorbed do not exhibit a transport maximum. Rate of transport determined by other factors (ie electrochemical gradient, membrane permeability, time fluid remains in tubule): recall: slower the fluid = more time for reabsorption. **important: passive water reabsorption by osmosis coupled to sodium reabsorption. Solute [ ] in interstitium increases with transport mechs drives osmosis of water from tubule to interstitium. Mostly through tight junctions b/w epithelial cells, and through cells themselves. Water can carry some solutes with it: solvent drag. Since reabsorption of water and substances is coupled to sodium changes in sodium reabsorption significantly influence water and solute reabsorption. Aquaporin insertion can also vastly increase h2o reabsorption.
