[Light- and electron-microscopic studies of the structure of normal bladder epithelium in female swine]

A light- and electron-microscope investigation was performed to examine the normal structure of the porcine urinary bladder. Tissue biopsies were studied obtained from 10 healthy female pigs (four weanling pigs, six sows). The bladder wall showed a typical stratification consisting of a tunica (t.) mucosae, t. submucosae, t. muscularis and t. serosa. The mucosa consisted of an epithelium transitionale, a lamina propria, and a lamina muscularis mucosae. The urothelium was composed of a basal layer, one or more intermediate layer(s), and a superficial layer. The urothelial cells of all layers were connected by desmosomes, while tight junctions linked adjacent superficial cells. Surface cells were lined by a layer of mucus, which is believed to provide an important barrier against bacterial infection. The surface of the superficial cells was also characterized by numerous irregularly arranged microplicae. By contrast, intermediate cells, which are assumed to be immature cell forms, showed microvilli-like structures. When desquamation of superficial cells takes place, differentiation of underlying intermediate cells is accompanied by merging of microvilli to form microplicae. The morphology of the bladder surface structures may play an important role in the ability of bacteria to adhere to the urothelium.