LIGHT-MICROSCOPE AND ELECTRON-MICROSCOPE STUDY OF THE STRUCTURE OF THE NORMAL BLADDER EPITHELIUM IN FEMALE PIGS

A light- and electron-microscope investigation was performed to examin e 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 consisti ng of a tunica (t.) mucosae, t. submucosae, t. muscularis and t. seros a. The mucosa consisted of an epithelium transitionale, a lamina propr ia, and a lamina muscularis mucosae. The urothelium was composed of a basal layer, one or more intermediate layer(s), and a superficial laye r. The urothelial cells of all layers were connected by desmosomes, wh ile tight junctions linked adjacent superficial cells. Surface cells w ere lined by a layer of mucus, which is believed to provide an importa nt barrier against bacterial infection. The surface of the superficial cells was also characterized by numerous irregularly arranged micropl icae. By contrast, intermediate cells, which are assumed to be immatur e cell forms, showed microvilli-like structures. When desquamation of superficial cells takes place, differentiation of underlying intermedi ate cells is accompanied by merging of microvilli to form microplicae. The morphology of the bladder surface structures may play an importan t role in the ability of bacteria to adhere to the urothelium.