The membranous labyrinth of the inner ear is filled with endolymph. Endolymph is uniquely high in potassium and low in sodium, resembling intracellular fluid. The structure responsible for actively secreting endolymph is:

• A Reissner's membrane
• B Basilar membrane
• C Spiral ligament fibrocytes
• D Stria vascularis ✓

Explanation

The stria vascularis (on the lateral wall of the scala media) is the primary site of endolymph production and maintenance of the endocochlear potential (+80 mV). It contains marginal cells, intermediate cells, and basal cells with Na-K-ATPase and NKCC1 transporters that actively pump potassium into the endolymph. Reissner's membrane forms the boundary between scala vestibuli and scala media and may also contribute but is not the primary secretory structure. Damage to the stria vascularis causes flat-type sensorineural hearing loss.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.