NORMAL ULTRASTRUCTURE OF THE KIDNEY AND LOWER URINARY-TRACT

The mammalian urinary tract includes the kidneys, ureters, urinary bla dder, and urethra. The renal parenchyma is composed of the glomeruli a nd a heterogeneous array of tubule segments that are specialized in bo th function and structure and are arranged in a specific spatial distr ibution. The ultrastructure of the glomeruli and renal tubule epitheli a have been well characterized and the relationship between the cellul ar structure and the function of the various components of the kidney have been the subject of intense study by many investigators. The lowe r urinary tract, the ureters, urinary bladder, and urethra, which are histologically similar throughout, are composed of a mucosal layer lin ed by transitional epithelium, a tunica muscularis, and a tunica seros a or adventitia. The present manuscript reviews the normal ultrastruct ural morphology of the kidney and the lower urinary tract. The normal ultrastructure is illustrated using transmission electron microscopy o f normal rat kidney and urinary bladder preserved by in vivo perfusion with glutaraldehyde fixative and processed in epoxy resin.