|Description:||Urinary Bladder and Urothelium
Joseph Alroy, D.V.M.
The urinary bladder is an organ that has to change its luminal volume.
This is achieved by the structures of both the smooth muscle, i.e.
detrusor, and the urothelium. Unlike the gastrointestinal tract in
which the smooth muscle cells are arranged in circular and
longitudinally to enable the peristaltic movement of the digestive
system, in the bladder the muscle bundles are interlaced to enable the
dilation and contraction of the organ. Likewise, the urothelium is also
able to contract and distend. The superficial and the intermediate
cells contain plaques of asymmetric unit membrane, in which the outer
leaflet is thicker than the inner leaflet. The plaques are joined by
"hinges" of interplaque plasma membrane. These plaques are synthesized
in the Golgi apparatus. The luminal membrane folds to form fusiform
vesicles when the organ is contracted.|