Bladder is an expandable vessel for the storage of urine. It is lined with an epithelium that is impermeable to water and ions.
Like the ureters, the bladder is composed of four concentric layers.
Transitional Epithelium (Urothelium) - consists of two to three cell layers in the upper ureter with up to ten cell layers near the bladder.
Umbrella Cells - the upper layer of cells that change shape depending on the distention of the bladder. Umbrella cells are frequently binucleate.
Dome-Shaped Umbrella Cells (#1 and #2) - rounded and bulge from the surface of the epithelium
Flattened Umbrella Cells (#1 and #2) - stretch over several underlying epithelial cells.
Lamina Propria - thick layer of dense irregular connective tissue rich in collagen and elastic fibers.
Muscularis Externa - loosely arranged smooth muscle in two layers (inner longitudinal and outer circular) in the upper ureter or three layers (inner longitudinal, middle circular and outer longitudinal) near the bladder.
Adventitia - loose connective tissue with blood vessels, nerves and adipose cells.