1. NITROGENOUS WASTES

2. 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

3. 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

4. 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

5. 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

6. 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

7. INSECTS: Malpighian Tubules
© 2016 Paul Billiet ODWS

8. 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