1.3.2 Tubular Reabsorption Flashcards
How do the apical and basolateral surfaces of the renal tubular epithelium differ?
Transport mechanisms, channels and receptors are different.
What are the two ways that substances can pass through the renal tubular epithelium?
The transcellular pathway
The paracellular pathway - between cells across the Zona Occludens
What provides the tight junctions in the renal tubular epithelium?
zonula occludens
Other than tight junctions, what are some other junctional complexes of renal epithelial cells?
Adhering junction
Desmosome
Gap junction
Hemi-desmosome
What establishes the electrochemical gradient in the basolateral membrane?
The combination of the Na-K-ATPase and K channels establish the gradient at -80mV
If there were no other channels in the apical membrane, the whole cell would be at -80mV
How does the apical membrane differ from the basolateral membrane?
The presence of other transporters in the apical membrane modify the gradient. So if there is a sodium channel there would be a depolarization of the apical membrane at -30mV
What are the functional properties of the proximal tubules?
High trans-cellular permeability to H2O and salt
High paracellular ion and H2O conduction
Absorbs 100% of glucose and amino acids
Secretes uric acid and drugs
High reabsorption rate/low gradient
What are the functional characteristics of the descending loop of Henle?
Moderate permeability to water and ions
Moderate rate/moderate gradient
What are the functional characteristics of the ascending loop of henle?
Moderate trans-cellular and para-cellular permeability
Reabsorbs 25% of salt
Reabsorbs NaCl and Mg
What are the functional characteristics of distal tubules?
Low trans and para cellular permeability
Reabsorption of NaCl
Reabsorption and secretion of K+
Variable reabsorption of NaCl depending on aldosterone
Variable reabsorption of H2O depending on ADH
What are the functional characteristics of the collecting tubules?
Low para and trans cellular permeability to H2O and ions
Secretion of H+ and HCO3-
Variable NaCl reabsorption depending on aldosterone
Variable H2O reabsorption depending on ADH
Discuss the reabsorption profile for major solutes along the nephron.
Understand that the majority of Mg reabsorption is done in the ascending Loop on Henle
What are the major apical membrane channels in the proximal tubule?
The Na-glucose symporter
Na-H antiporter
What is the important apical membrane channel in the thick ascending loop of henle?
Na+-K+-2Cl- cotransporter
What is the important apical membrane channel in the distal tubule?
In the early segment of the tubule, Na+ and Cl- are reabsorbed via a Na+-Cl- symporter in the apical membrane.