Urinary System

The urinary system is responsible for a variety of physiological processes, including osmoregulation, blood pressure and volume regulation, red blood cell production, calcium absorption, toxin metabolism, and excretion. The nephron is the functional unit of the kidney and is composed of the glomerulus and renal tubules. The products of the kidney include urine, the enzyme hormone renin, and the hormones erythropoietin and calcitriol, which is the active form of vitamin D. These common mammalian renal functions, as well as overall gross and histological structure, are similar between mice, rats, and humans. Species differences in renal physiology are reflected in the nephron ratio and number and also the morphology of vascular bundles, renal papillae, and medulla. Rodents, especially males, make highly concentrated urine with a high protein content. Sexual dimorphism may be present in both the rodent kidney. Ultrastructural differences also exist between rodents and humans. Renal size as well as responses to various drugs and compounds can differ significantly depending on rodent sex within and between strains. These potential differences must be considered during study design, interpretation of clinical data, and postmortem evaluations.