Options for histological study of the structure and ultrastructure of human urinary bladder epithelium

Abstract

The urothelium lines all urinary passages, with exception of the distal portions of the urethra. For the first time the structure of the human bladder was described by Leonardo Da Vinci in 15th century, however, the exact ultrastructure and function of the bladder’s epithelium have not been fully understood. The aim of our study was to investigate the structure of normal human urinary bladder epithelium with methods of classical histology, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). We obtained biopsies from non-tumor areas from the human urinary bladder of tumor-bearing patients during transurethral resections of these tumours in general or spinal anaesthesia. Totally we investigated biopsies from 20 patients, 16 males and 4 females. The mean age of this group of patients was averaged 66.5 years. The urothelium is comprised of three cell types including polyhedral basal cells, piriform intermediate cells, and superficial umbrella cells. In human urinary bladder epithelium we found a direct connection between intermediate cells and the basement membrane. These thin cytoplasmic projections are detectable not only on slides for light microscopy (semi-thin sections), but also in transmission electron-micrographs. In semi-thin sections we found also direct connections between superficial umbrella cells and basement membrane. These connections we were not able to verify via transmission electron-microscopy. Nevertheless our results show that the human urinary bladder urothelium is a special type of pseudostratified epithelium and each cell has a thin cytoplasmic projection with a direct contact with basement membrane.