UREA EXCRETING ANIMALS NITROGENOUS WASTES IN THE BODY

UREA EXCRETING ANIMALS • NITROGENOUS WASTES IN THE BODY TEND TO FORM TOXIC AMMONIA, WHICH MUST BE EXCRETED. MAMMALS SUCH AS HUMANS EXCRETE UREA, WHILE BIRDS, REPTILES, AND SOME TERRESTRIAL INVERTEBRATES PRODUCE URIC ACID AS WASTE

• URICOTHELIC ORGANISMS TEND TO EXCRETE URIC ACID WASTE IN THE FORM OF A WHITE PASTE OR POWDER. • Ureotelic animals that secrete primarily nitrogenous waste material

• MAMMALS, INCLUDING HUMANS, ARE THE PRIMARY PRODUCERS OF UREA. BECAUSE THEY SECRETE UREA AS THE PRIMARY NITROGENOUS WASTE PRODUCT, THEY ARE CALLED UREOTELIC ANIMALS. • UREA SERVES AN IMPORTANT ROLE IN THE METABOLISM OF NITROGENCONTAINING COMPOUNDS BY ANIMALS. IT IS THE MAIN NITROGEN-CONTAINING SUBSTANCE IN THE URINE OF MAMMALS.

IN OTHER AMIMALS • APART FROM MAMMALS, UREA IS ALSO FOUND IN THE URINE OF AMPHIBIANS, AS WELL AS SOME FISH. INTERESTINGLY, TADPOLES EXCRETE AMMONIA, BUT SHIFT TO UREA PRODUCTION DURING METAMORPHOSIS.

Uric Acid IN BIRDS AND REPTILES, URIC ACID IS THE MAJOR END-PRODUCT OF PROTEIN METABOLISM. • IT IS PRODUCED BY THE LIVER AND EXCRETED BY KIDNEY TUBULES; IMPAIRED ELIMINATION IS AN INDICATION OF RENAL DISEASE •

APPROXIMATELY 90% OF URIC ACID IS SECRETED BY THE PROXIMAL TUBULES IN AVIAN SPECIES. EXCRETED UA PASSES THROUGH THE CLOACA AND IS RETROPULSED BACK INTO THE RECTUM AND CECUM, WHERE IS IT BROKEN DOWN BY BACTERIA AND IS REABSORBED. • AT LEAST 60% OF RENAL FUNCTION MUST BE LOST FOR AN ELEVATION IN •

SIGNIFICANCE OF URIC ACID AND GUANINE HAVE AN ADVANTAGE OF CARRYING AWAY FOUR NITROGENOUS ATOM PER MOLECULE. • THE NITROGEN ATOM IN URIC ACID ARISE FROM BREAKDOWN OF THE GLYCINE , ASPARTATE AND GLUTAMINE. •

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