Facet cell

Facet cells (also known as umbrella cells,[1] capping cells, superficial urotheliocytes) are a type of cells located in the renal pelvis, the ureter and the urethra. Facet cells form the outermost layer of the urothelium, which is a special type of epithelium found in the above-mentioned structures. Umbrella cells are special in that they can contain multiple nuclei, their apical membrane contains numerous invaginations which allows the cells to stretch during miction and they are linked together with tight junctions which:

  • prevents urine from leaking in the epithelium
  • creates an osmotic barrier. Indeed, urine osmolarity can range from 50 to 1200 mmol/L while the normal body osmolarity is 290 mmol/L. The difference between the two could lead to fluid entering or exiting the ureter due to the osmotic pressure.[2]

References
  1. Born, Martin; Pahner, Ingrid; Ahnert-Hilger, Gudrun; Jöns, Thomas (July 2003). "The maintenance of the permeability barrier of bladder facet cells requires a continuous fusion of discoid vesicles with the apical plasma membrane". European Journal of Cell Biology. 82 (7): 343–350. doi:10.1078/0171-9335-00326. PMID 12924629.
  2. Lüllman-Rauch (2008). Histologie 1er cycle des études médicales. De Boeck Supérieur. ISBN 9782804156923.
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