Animal Waste and Excretion Processes

Waste Products

• Animals generate various waste products through metabolic processes and excess ingestion.
• These wastes include ammonia, urea, uric acid, carbon dioxide, water, and ions like sodium, potassium, chloride, phosphate, and sulfate.

Elimination of Wastes

• The body eliminates these waste products, either fully or partially, through excretion.
• Excretion focuses on removing nitrogenous wastes – ammonia, urea, and uric acid.

Ammonia

• Ammonia is the most toxic form of nitrogenous waste.
• Its elimination requires a large amount of water.
• Ammonotelic animals, like bony fish, aquatic amphibians, and aquatic insects, primarily excrete ammonia.
• Ammonia, due to its high solubility, is excreted through diffusion across body surfaces or gill surfaces in fish.
• Kidneys play a minimal role in removing ammonia in these animals.

Urea

• Urea is less toxic than ammonia, allowing for water conservation.
• Ureotelic animals, such as mammals, terrestrial amphibians, and marine fish, mainly excrete urea.
• Ammonia produced during metabolism is converted into urea in the liver.
• Urea enters the bloodstream and is then filtered and excreted by the kidneys.
• Some urea can be retained in the kidney matrix to regulate osmolarity.

Uric Acid

• Uric acid is the least toxic form of nitrogenous waste, allowing for maximum water conservation.
• Uricotelic animals, including reptiles, birds, land snails, and insects, excrete uric acid.
• Uric acid is excreted as a pellet or paste, minimizing water loss.