Structure of the lymphatic microcirculation in the human urinary bladder with different intraluminal pressure and distension.

The localization, morphology and fine structure of initial lymphatic vessels in themucosa of the empty and distended urinary bladder were studied. Endoscopic transurethralbiopsies of the empty (collapsed) bladder showed under light and electron microscopynumerous intramural lymphatics with a dilated lumen and thin profile. Contacts betweenendothelial cells were single, overlapping, interlocking, and open while the perivascularconnective tissue was filled by fascicles of collagen fibers. In the most superficial layer(subepithelial mucosa), lymphatics were not seen. Biopsies obtained under elevatedintraluminal pressure and distension showed on light and electron microscopy lymphaticvessels with small lumens characteristically reduced to irregular slits. Endothelial cellcontacts were simple or overlapping; open junctions were rare. The perivascular connectivetissue was dense and collagen and elastic fibers often abutted one another. These findingssupport that with a distended or expanded urinary bladder, the effect of increasedintraluminal pressure on the superficial (mucosal) layer radially pulls on the connectivetissue that in turn compresses the initial lymphatics thereby restricting lymph transport.