Perilymph is an

extracellular fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 50–60% (range 45 to 75%) of total body weight; women and the obese typically ha ...

located within the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

. It is found within the scala tympani and scala vestibuli of the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the organ of Cort ...

. The ionic composition of perilymph is comparable to that of plasma and

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

. The major

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

in perilymph is

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

, with the values of

and

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

concentration in the perilymph being 138 mM and 6.9 mM, respectively. It is also named Cotunnius' liquid and liquor cotunnii for

Domenico Cotugno Domenico Felice Antonio Cotugno (January 29, 1736 – October 6, 1822) was an Italian people, Italian physician. Biography Born at Ruvo di Puglia (Province of Bari, Apulia) into a family of humble means, Cotugno underwent physical and economic ...

Structure

The

has two major parts, the cochlea and the vestibular organ. They are connected in a series of canals in the temporal bone referred to as the

bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the ...

. The bone canals are separated by the membranes in parallel spaces referred to as the membranous labyrinth. The membranous labyrinth contains

endolymph Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. ...

, and is surrounded by perilymph. The perilymph in the bony labyrinth serves as connection to the

of the subarachnoid space via the perilymphatic duct.

Composition

Perilymph and

have unique ionic compositions suited to their functions in regulating

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase (typi ...

impulses of

hair cells Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

necessary for hearing. The

electric potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...

of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of potassium cations (K⁺) in endolymph and higher sodium (Na⁺) in perilymph. This is referred to as the endocochlear potential. Perilymph is the fluid contained within the bony labyrinth, surrounding and protecting the membranous labyrinth; perilymph resembles extracellular fluid in composition (sodium salts are the predominant positive electrolyte) and, via the cochlear aqueduct (sometimes referred to as the "perilymphatic duct"), is in continuity with

. Endolymph is the fluid contained within the scala media of the membranous labyrinth of the inner ear and within the semicircular canals of the vestibular apparatus; endolymph resembles

intracellular fluid The human body and even its individual body fluids may be conceptually divided into various fluid compartments, which, although not literally fascial compartment, anatomic compartments, do represent a real division in terms of how portions of the ...

in composition (potassium is the main cation). Apart from the importance in the electric cochlear potential, the perilymph also contains a large number of proteins, e.g. extracellular enzymes and immunoglobulins. These proteins are important for the immune response and metabolism among others physiological functions.

Clinical significance

It has also been suggested that perilymph and endolymph participate in a unidirectional flow that is interrupted in Ménière's disease.

References

External links

{{Authority control Ear Body fluids