The Architecture of the Musculature of the Guinea-Pig Ureter as Examined by Scanning Electron Microscopy

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Abstract
The muscular architecture of the guinea-pig ureter at different levels was examined by scanning electron microscopy. In the middle portion of the ureter, bundles of smooth muscle fibers were rather randomly oriented with respect to each other and to the long axis of the ureter, forming an iregular network. The muscle fibers of the upper ureter were mostly circularly oriented with a few outermost longitudinal muscle bundles. In the lower portion, the muscle bundles were predominantly longitudinally oriented overlying a deeper circular muscle layer. At any level examined, individual muscle fibers were about 100-150 .mu.m long and about 5 .mu. wide, exhibiting a generally smooth surface. The adjacent muscle fibers were frequently interconnected by small lateral projections. In the pelvic portion, thin and short longitudinal muscle bundles were scattered over the inner circular muscles. Individual muscle fibers were spindle-shaped, about 70 .mu.m long, and 5 .mu.m wide at their thickest central portion. They were characterized by a rugged surface with many irregular projections and depressions. These muscle fibers may represent pacemaker cells. The findings were discussed in relation to the peristaltic movement of the ureter.