glomerular capillary

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normal
glomerular capillary
AA
EA
usually, there is a combination of ?AA and ?EA
resistance that attempts to maintain GFR in the
face of decreasing RBF, until ?RBF becomes severe
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Proximal tubular reabsorption

• primary (key) driving force
• Na-K-ATPase activity primary active transport
• generates both concentration and electrical
  gradients favoring Na movement from the tubular
  lumen into the PT cells ? peritubular capillary
• 2nd driving force
• Na/H antiporter in lumenal membrane
  secondary active transport

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Proximal tubular reabsorption

• 3rd driving force
• Na/X (glucose, AA) cotransporters in lumenal
  membrane secondary active transport
• 4th driving force solvent drag
• Na and water reabsorption fuels passive
  reabsorption of many other substances (Ca,
  Mg, K, urea, Na, Cl-)

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Proximal tubular reabsorption
apical electrochemical gradient for Na
reabsorption
tubular lumen
uniport
peritubular capillary
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Proximal tubular reabsorption
secondary active transport
tubular lumen
Na gluc, AA, P, S, organic ions
Na
symport (cotransport)
H
antiport (countertransport)
passive or facilitated diffusion
peritubular capillary
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Proximal tubular reabsorption
As filtrate passes down the proximal tubule,
solvent drag facilitates reabsorption of K,
Ca, Mg and further passive Na reabsorption
tubular lumen
K
favorable concentration gradients
via the paracellular pathway
Ca
Mg
Na
peritubular capillary
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Proximal tubular reabsorption - Starling forces
peritubular capillary uptake
Ka (Pint pptc) (Pptc pint)
start PT
end PT
peritubular capillary
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Principal Cells (aldosterone) Na/Cl
reabsorption K secretion
Intercalated Cells K reabsorption H secretion