Compared with saliva collected at rest, saliva collected during maximal stimulation (high flow rate) shows which of the following changes?
- A Decreased bicarbonate concentration
- B Increased potassium concentration
- C Increased sodium concentration ✓
- D Becomes isotonic with plasma
Correct answer: C. Increased sodium concentration
Explanation
Salivary ducts reabsorb Na and Cl and secrete K and HCO3. At high flow rates, contact time between saliva and ductal epithelium falls, so less Na is reclaimed and luminal Na rises toward plasma levels. Potassium actually falls at high flow because ductal K secretion is fixed while volume rises, and bicarbonate rises markedly with stimulation because stimulated acinar secretion is HCO3 rich. Even at maximal flow the final saliva remains hypotonic because ducts are water impermeable.
Reference: Ganong Review of Medical Physiology, 27th ed.
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