ln response to an increase in GFR, the proximal tubule and the loop of Henle demonstrate an increase in the rate of Na reabsorption. This phenomenon is called
Autoregulation
Glomerulotubular balance
Mineralocoicoid escape
Saturation of tubular transpo
Autoregulation refers to the relative constancy of renal blood flow and GFR despite changes in aerial blood pressure. Mineralocoicoid escape refers to the fact that the salt-retaining action of mineralocoicoids does not persist but is overpowered by factors that promote renal Na+ excretion. Saturation of transpo occurs when the maximal rate of tubular transpo is reached. Tubuloglomerular feedback results in afferent aeriolar constriction when fluid delivery to the macula densa is increased; it contributes to renal autoregulation. Glomerulotubular balance: More the filtered load, more the reabsorbed load (load-dependent reabsorption). What is reabsorbed is a constant percentage and not a constant amount. This helps in preserving the solute. The possible mechanism for glomerulotubular balance: As more fluid comes out of the glomerulus (due to increase in GFR), the protein concentration and therefore the oncotic pressure in the plasma increases. When the plasma comes to the peritubular capillaries, there is an increased oncotic pressure; this results in pulling the excess water in the tubular lumen into the capillaries. Along with the flow of water, sodium is also reabsorbed (this is known as bulk flow or solvent drag).
Renal physiology