Urothelium
The urothelium (also transitional epithelium ) is the name given to the multi-layered covering tissue ( epithelium ) of the lower urinary tract ( renal pelvis , ureter , urinary bladder , upper part of the urethra ).
Transitional cells are highly prismatic in the unfilled state of the urinary tract, but flatten out with increasing filling. Expansion is also possible through reserve folds in the cell membrane . This ensures that the urinary organs can adapt to different filling conditions.
In the unfilled urinary bladder, the thickness of the urothelial layer is five to six cells. The lowest cells are cuboid, the middle polyhedral and the uppermost are rounded in shape. Once the bladder is full, this is reduced to three to four cells, with the deeper cells being cuboid and the superficial ones being flattened.
The cells closest to the surface have a special membrane that maintains the osmotic barrier between urine and interstitial body fluid . The main component of this membrane are cerebrosides . The urothelium has a certain glycocalix , which is called uroplakine in its protein structure. Since urine can also contain toxins and pathogens, it also fulfills functions in fighting infections and responding to injuries.
The cover cells of the urothelium show a surface differentiation that appears condensed under the light microscope, the crusta .
The transitional epithelium consists of three different layers (stratum basale, stratum intermedium and stratum superficiale). The superficial cells are also known as cover cells and are often two-nucleus.
Web links
- M. Lazzeri: The physiological function of the urothelium - more than a simple barrier. In: Urol Int. 76, 4, 2006, pp. 289-295. PMID 16679827