Lecture 05 - Tubular Function

Lecture 05 - Tubular Function - Renal: Tubular Function The...

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Renal: Tubular Function The big picture Sodium, chloride, and water are freely filterable at the glomerulus Our survival is dependent on typically >99% of filtered sodium, chloride, and water being reabsorbed in order for us to not pee out our extracellular fluid we need to reabsorb almost all that is filtered Kidney is largely responsible for maintaining homeostasis in the setting of large variations in NaCl and water intake kidney will fine tune how much would get excreted or help onto Next four lectures will largely deal with how Na + , Cl - , and water are handled by the nephron (some related content as well) Introduction of other content which will be explored later in more depth Crossing the epithelium (reabsorption process): one step vs. two steps - in order to get across the epithelium: - one step process o paracellular reabsorption o this happens in epithelium with tight junction (the blue ball) o it is passive that goes through tight junctions o driven by electro-chemical gradient between the lumen and the interstitial compartment - two step process o transcellular o influx/efflux transporter (different transporter in apical and basolateral) o Comes in the lumen and goes through the basolateral (this is the membrane that goes around except for the one side of apical touching the lumen) o The polarization will take a while when the kidney is damaged because the transporter must figure out where it has to go - In tubular there is endocytosis - across the tubular epithelium (fuse with lysosomess) and can leave the cell through basolateral and return to circulation - Transcytosis - basolateral membrane --> lumen it is a secretary process and important in the defense mechanism of the GI tract ***but most processes will be transcellular and paracellular Summary of transmembrane solute transport mechanisms Diffusion Uniport(ers) Symport(ers) Antiport(ers) Channels Active transport (ATP dependent) Categories of transporters Uniporters Movement of single solute species Requires solute to bind to site “facilitated diffusion” Example: GLUT family facilitate glucose transport Symporters Movement of 2 or more species in the same direction “cotransport” Sodium and glucose together (SGLT protein family) Sodium, potassium, and chloride together (think ascending limb) One of the solutes moves down its electrochemical gradient, providing the energy to move one or more up their gradients Antiporters and antiport
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Also referred to as “exchange” or “counter transport” Na + -H + antiport important in the proximal tubule -- NHE Cl - - HCO3 - antiport also important in the kidney Primary active transporters Move 1-2 solutes up their electrochemical gradient, using energy from ATP Key examples in the kidney: Na + -K + ATPase H + ATPase Ca ++ ATPase How is channel permeability regulated? Gating (permeability)
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Lecture 05 - Tubular Function - Renal: Tubular Function The...

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