Three-dimensional arrangement of collagen and elastin fibers in the human urinary bladder: a scanning electron microscopic study.

To clarify the arrangements of collagen and elastin fibers of the urinary bladder, we examined 9 human (male, aged 42 to 72) urinary bladders by scanning electron microscopy with chemical digestion methods. The mucosal layer was divided into 3 portions according to the collagen arrangement: the superficial portion interwoven densely by collagen fibrils, the middle portion layered by flat bundles of collagen fibrils and the deep portion made of a loose network of twisted collagen bundles. In the muscular layer, the smooth muscle fascicles were firmly covered with collagen sheets, while each muscle cell in a fascicle was accommodated by a thin sheath of collagen fibrils. The serosal layer consists of wavy collagen bundles piled up in a sheet, which was intercalated by clusters of adipose cells. Elastic fibers were, on the other hand, sparse throughout the bladder wall, except for denser networks around the blood vessels and muscle fascicles and beneath the peritoneal mesothelium. The arrangements of these components were discussed in relation to the mechanical function and compliance of the urinary bladder.