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NBME 20 Answers

nbme20/Block 4/Question#16

An investigator wishes to determine the ...

Ductal ion reabsorption is more efficient at low flow rates

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submitted by usmleuser007(22),

Salivary secretion 1. At low flow = High concentration of potassium; low concentrations of sodium, bicarb, & chloride 2. at high flow = low concentration of potassium; high concentrations of sodium, bicarb, & chloride


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submitted by sinforslide(4),

Overview of Saliva production:

  1. Acinar cells secrete initial saliva, which is isotonic to plasma.
  2. Ductal cells modify initial saliva, causing reabsorption of Na+, Cl- and secretion of K+ and HCO-. -> higher K+ and HCO- concentrations, lower Na+ Cl- concentrations in saliva. In this process, MORE NaCl is reabsorbed, meaning that saliva ends up being hypotonic to plasma.

Ductal reabsorption process is hindered in high-flow states, which causes isotonic saliva