Lizard Urinary System

Kidneys

The kidneys are metanephric in all species. In iguanas they lie within the pelvic canal on either side of the colon. Nephromegaly can result in obstruction of the colon as it passes between the kidneys within the pelvic canal.

• Granulomatous nephritis causing colonic obstruction or dystocia is relatively common in the green iguana.
• The posterior segment of the kidney (called sexual segment) in some male geckos, skinks and iguanids is sexually dimorphic. It swells during the breeding season, contributing to the seminal fluid; its colour may also change dramatically and should not be misinterpreted as pathology.

Uric Acid

Uric acid is the main form of nitrogenous waste with lesser amounts of ammonia and urea depending on the species, the natural environment and degree of water conservation required. Uric acid is excreted by tubular secretion rather than urea by glomerular filtration.

Bladder

Most lizards have a urinary bladder where the urine may be modified. Urinalysis may therefore not indicate renal function. A thin-walled bladder is present in most lizards and helps water retention. When absent, urine is stored in the distal colon. It connects to the cloaca by a short urethra which means that urine waste flows from the kidney through the ureter into the urodeum of the cloaca before entering the bladder (or colon for species lacking a bladder), resulting in non-sterile urine, unlike mammals.

Reflux urine is concentrated.

• Water deprivation and diets containing excessive levels of protein can cause cystic calculi.

References

• Mader, D.R. (2005). Reptile Medicine and Surgery. Saunders. pp. 1264. ISBN 072169327X