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Lizards and snakes are different to mammals in several aspects of nitrogenous excretion. [[Uric acid|Uric acid]] is the primary nitrogenous waste product of most reptilian species.  

Lizards and snakes are different to mammals in several aspects of nitrogenous excretion. Uric acid is the primary catabolic end-product of protein, nonprotein nitrogen and purines in reptiles. It is synthesised in the liver and excreted by renal tubular secretion.  

* Reptile kidneys have relatively few nephrons, lack a renal pelvis and loop of Henle and therefore they cannot concentrate urine in the kidney above blood osmolarity. However, urine may be concentrated in the distal colon until passed with the faeces.  

* Reptile kidneys have relatively few nephrons, lack a renal pelvis and loop of Henle and therefore they cannot concentrate urine in the kidney above blood osmolarity. However, urine may be concentrated in the distal colon until passed with the faeces.  

* The excretion of urea or ammonia results in significant water loss which explains why they are excreted in significant amounts only in aquatic and semiaquatic species.  

* The excretion of urea or ammonia results in significant water loss which explains why they are excreted in significant amounts only in aquatic and semiaquatic species.  

* Water can be reabsorbed from the bladder resulting in postrenal concentration of urine; insoluble [[Uric acid|uric acid]] can be excreted which allows for water conservation.  

* Water can be reabsorbed from the bladder resulting in postrenal concentration of urine; insoluble uric acid can be excreted which allows for water conservation.  

* Fluid is pumped from the contents of the colon by osmotic forces.  

* Fluid is pumped from the contents of the colon by osmotic forces.  

==References==

==References==