endolymfe

Endolymfe, or endolymph, is the fluid that fills the membranous labyrinth of the inner ear, including the scala media of the cochlea and the vestibular apparatus. It creates the ionic environment necessary for the proper functioning of hair cells involved in hearing and balance.

The endolymfe is produced and maintained by the stria vascularis, a vascularized epithelium lining the lateral wall of the cochlear duct. Ion transport processes in the stria vascularis generate a high potassium (K+) environment and a distinctive electrochemical potential that differs from surrounding fluids. Endolymphe circulates within the lumen of the membranous labyrinth and is drained by the endolymphatic sac and duct, which help regulate its volume and composition.

Ionic composition is characteristic of endolymfe, with a high concentration of potassium (approximately 150 mM) and very low sodium (Na+) levels, compared with surrounding perilymph. The endolymph also contributes to a notable endolymphatic potential, an electrical potential of about +80 millivolts relative to perilymph, which amplifies the sensory transduction carried out by hair cells.

Functionally, the endolymfe provides the chemical milieu needed for mechanotransduction by hair cells in the cochlea and vestibular organs. Disturbances in endolymph production, composition, or drainage can lead to endolymphatic hydrops, a condition associated with Meniere’s disease, characterized by vertigo, tinnitus, and fluctuating hearing loss.

See also: endolymphatic hydrops, stria vascularis, inner ear anatomy, hair cell transduction.