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Facet cells (also known asumbrella cells,^[1] capping cells, superficial urotheliocytes) are a type of cells located in therenal pelvis, theureters, and theurethra. Umbrella cells form the outermost layer of theurothelium, which is a special type ofepithelium found in therenal pelvis, theureters, and theurethra. Umbrella cells are special in that they can containmultiple nuclei. Theirapical membrane contains numerousinvaginations, which allows the cells to stretch duringurination. Umbrella cells are linked together with tightjunctions which:

• prevents urine from leaking through theepithelium.
• creates anosmotic barrier. Urineosmolarity can range from 50 to 1200mmol/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 theosmotic pressure.^[2]

Umbrella cells containuroplakin ia,uroplakin ib, uroplakin ii, and uroplakin iii.^[3] These increase the strength of theurothelium.^[3]

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