In the inner ear, the electrolyte composition of endolymph closely resembles which intracellular fluid characteristic?
- A High sodium, low potassium
- B Balanced sodium and potassium concentrations
- C High potassium (~150 mEq/L), low sodium (~1 mEq/L) ✓
- D High calcium, low potassium
Correct answer: C. High potassium (~150 mEq/L), low sodium (~1 mEq/L)
Explanation
Endolymph is unique among extracellular fluids — it is rich in potassium (~150 mEq/L) and low in sodium (~1 mEq/L), resembling intracellular fluid. This composition is maintained by the stria vascularis via active Na-K-ATPase pumps. The endocochlear potential (+80 mV) relative to perilymph is critical for mechanotransduction. Disruption of this balance (e.g., Menière's disease) causes cochleo-vestibular dysfunction.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.