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NITROGENOUS WASTES
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Nitrogenous wastes Nitrogenous wastes are synthesized by animals from excess amino acids Unlike lipids and carbohydrates amino acids are not stored in the body They are deaminated by the liver tissues and the amino group has to be excreted. © 2016 Paul Billiet ODWS
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NH2.CHR.COOH + H2O NH3 + O CHR.COOH
Deamination NH2.CHR.COOH + H2O NH3 + O CHR.COOH Transaminase Amino acid Water Ammonia Keto acid Toxic, it must be excreted Can be converted into glucose and recycled © 2016 Paul Billiet ODWS
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Three types of nitrogenous wastes are used by the vertebrates
Ammonia Urea Uric acid Ammonia is a direct product of deamination. In the liver Urea is produced from ammonia. This also takes place in the liver tissues 2NH3 + CO2 CO(NH2)2 + H2O Uric acid is formed directly from amino acids in a series of reactions that produces its complex ring structure. © 2016 Paul Billiet ODWS
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Excreted by insects, most reptiles and all birds
The use of these three forms of nitrogenous wastes follows a pattern in animals AMMONIA UREA URIC ACID NH3 CO(NH2)2 C5H4O3N4 O N N H NH2 C O Highly toxic Moderately toxic Not very toxic Highly soluble Moderately soluble Insoluble Excreted mainly by aquatic invertebrates, osteichthyes (bony fish) and tadpoles Excreted by chondricthyes (sharks and rays), terrestrial amphibians and mammals Excreted by insects, most reptiles and all birds Increasing water stress → © 2016 Paul Billiet ODWS
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So why don’t mammals excrete uric acid?
Mammals split off from early reptiles before uric acid excretion evolved Modern birds Modern reptiles Modern mammals Dinosaurs Uric acid excretion Diapsids 300Ma Early mammals Early reptiles Urea excretion Amphibians © 2016 Paul Billiet ODWS
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INSECTS: Malpighian Tubules
© 2016 Paul Billiet ODWS
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The Malpighian tubule function
Hemolymph Excretion Hind gut K+ Nitrogenous wastes Active Uric acid precipitates Potassium urate Reabsorption Osmosis Tubule H2O H2O K+ © 2016 Paul Billiet ODWS
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