The Important Function of the Endolymphatic Sac

New Understanding of the Endolymphatic Sac

In studying the structure of the inner ear, either in high school or college anatomy class, you may have become familiar with the details: the cochlea, the inner ear canals, the auditory nerve, etc. But one small, but newfound important detail never mentioned before but always present is the endolymphatic sac.
Unknown Function Of The Endolymphatic Sac
For centuries no one knew for sure the function of this peculiar sac, though hypotheses existed. Its location deep in the inner ear (surrounded by dense bone) made the study of the endolymphatic sac extremely difficult. But, now new light has been shed on this tiny component of the inner ear thanks to research conducted by Harvard Medical School (HMS) research fellow in systems biology, Ian Swinburne, and his postdoctoral advisor Sean Megason, HMS associate professor of systems biology.
In studying zebrafish, Ian discovered the endolymphatic sac was much easier to see and examine. It was through this examination that he noticed the sac was pulsing in a rhythmic fashion. Puzzled by the movement, Ian and Sean collected as many microscopic studies of the endolymphatic sac as they could from laboratories all over the world.
Fluid Regulation
What they discovered was that the sac was actually a fluid pressure regulating mechanism for the inner ear. Upon intense, prolonged study and partnership with other key scientists, these two researchers discovered unique way cells of the endolymphatic sac connected with each other.
Cell Structure
Normally cells of tissues like these connect to each other tightly so as to provide a leak-proof barrier. The cells of the endolymphatic sac, however, were connected loosely with small gaps between the cells. Overlapping the cells were flap style projections that covered the cells called lamella. When too much liquid accumulated in the sac, these “lamellar barriers” as the two researchers refer to them, open allowing fluid to escape. Once pressure is normalized, the flaps close again.
Other Parts Of The Body
This new discovery has significant implications for the physiology behind inner ear function. Similar endolymphatic sac-like structures have been found in other areas of the body such as the eyes, brain, and kidneys. If these structures behave in a similar fashion, there may be real possibilities for the treatment of pressure imbalance disorders such as glaucoma and Meniere’s disease.
Genetic Implications
Of particular significance is the possible identification of poor functioning inner ear pressure control as a result of genetic mutations. Swinburne discovered the pulsating endolymphatic sac because of a genetic mutation in one of the zebrafish he was studying that caused the enlargement of the endolymphatic sac because of improper functioning. This and similar mutations have been known to cause glaucoma in humans, which is caused by fluid build up in front of the eye.
More research needs to be conducted in the meantime to understand just how these lamellar barriers are triggered. Scientists will need to determine if the opening of the barriers is caused by physical pressure build up, or if a chemical indicator is triggered instead.

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