34 - Lower Urinary Tract

Abstract

This chapter describes toxicologic pathology of lower urinary tract. The lower urinary tract extends from the kidney pelvis bilaterally through the ureters, into the urinary bladder, and ultimately out the urethra. It functions primarily to transport urine formed in the kidneys to the urinary bladder for storage until ultimate excretion. The structure and function of the lower urinary tract are similar in all mammals, including the structure of a unique lining epithelium, the urothelium. The urothelium lining the kidney pelvis is a continuation of the single cell epithelial lining of the renal papilla. It becomes the usual three-celled thickness of rodent urothelium within a short distance of the fornix, increasing in cell number as it approaches the ureter. The urothelium (particularly of the urinary bladder) can be the target for toxic effects because it comes in contact with most chemicals or their metabolites excreted in the urine in concentrated quantities. The response to toxicity and the development of tumors are similar in rats and mice and both have numerous similarities to the response in humans, making these species excellent animal models for a variety of human disorders.