A mathematical model of XXXX proximal tubule and loop of Henle.

@entity13897 @entity6 @entity19 @entity4218 @entity10200 @entity71536 @entity35 @entity4854
Proximal tubule and loop of Henle function are coupled, with proximal transport determining loop fluid composition, and loop transport modulating glomerular filtration via tubuloglomerular feedback (TGF). To examine this interaction, we begin with published models of the superficial @entity35 proximal convoluted tubule (PCT; including flow-dependent transport in a compliant tubule), and the @entity35 thick @entity4218 ( @entity4218 ). Transport parameters for this PCT are scaled down to represent the proximal straight tubule (PST), which is connected to the thick @entity4218 via a short descending limb. Transport parameters for superficial PCT and PST are scaled up for a juxtamedullary nephron, and connected to @entity4218 via outer and inner medullary descending limbs, and inner medullary thin @entity4218 . Medullary interstitial solute concentrations are specified. End- @entity4218 hydrostatic pressure is determined by distal nephron flow resistance, and the TGF signal is represented as a linear function of end- @entity4218 cytosolic Cl concentration. These two distal conditions required iterative solution of the model. Model calculations capture inner medullary countercurrent flux of urea, and also suggest the presence of an outer medullary countercurrent flux of ammonia, with reabsorption in @entity4218 and secretion in PST. For a realistically strong TGF signal, there is the expected homeostatic impact on distal flows, and in addition, a homeostatic effect on proximal tubule pressure. The model @entity10200 threshold is compatible with @entity35 data, and predicted @entity13897 with selective 1Na(+):1glucose cotransporter ( @entity71536 ) inhibition comports with observations in the @entity19 . Model calculations suggest that enhanced proximal tubule Na(+) reabsorption during @entity4854 is sufficient to activate TGF and contribute to @entity6 .
