The endolymph of the membranous labyrinth has a unique ionic composition (high K+, low Na+) resembling intracellular fluid. It is produced by which structure and absorbed by which structure?

• A Produced by the dark cells of the utricle/saccule; absorbed by the crista ampullaris
• B Produced by the Reissner membrane; absorbed by the round window
• C Produced by the spiral ligament; absorbed by the oval window
• D Produced by the stria vascularis of the cochlea; absorbed by the endolymphatic sac ✓

Explanation

Endolymph is produced by the stria vascularis (highly vascularised epithelium on the outer wall of the cochlear duct) which actively secretes K+ via Na+/K+-ATPase and KCNQ1 channels. Endolymph drains into the endolymphatic duct and is absorbed by the endolymphatic sac (located in the posterior fossa under the dura). Blockage of this absorption (due to endolymphatic hydrops) produces Ménière's disease — episodic vertigo, fluctuating sensorineural hearing loss, tinnitus, and aural fullness. Reissner's membrane separates the scala media from the scala vestibuli but its primary role is in maintaining the endolymph-perilymph barrier.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.