Working of excretory system
Hyderabad: This article is in continuation to the previous article that focused on regulation of cardiac activity, disorders of circulatory system and coronary artery diseases (CADs). In this article, we will discuss introduction to the excretory system of living beings. Excretory products and their elimination Animals accumulate ammonia, urea, uric acid, carbon dioxide, water and […]
Hyderabad: This article is in continuation to the previous article that focused on regulation of cardiac activity, disorders of circulatory system and coronary artery diseases (CADs). In this article, we will discuss introduction to the excretory system of living beings.
Excretory products and their elimination
Animals accumulate ammonia, urea, uric acid, carbon dioxide, water and ions like Na , K , Cl–, phosphate, sulphate, etc., either by metabolic activities or by other means like excess ingestion.
• These substances have to be removed totally or partially.
• Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals.
• Ammonia is the most toxic form and requires large amount of water for its elimination, whereas uric acid, being the least toxic, can be removed with a minimum loss of water.
Ammonotelic animals
• Many bony fishes, aquatic amphibians and aquatic insects mainly excrete ammonia and are called ammonotelic animals.
• Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions.
• Kidneys do not play any significant role in its removal.
Ureotelic animals
• Mammals, many terrestrial amphibians and marine fishes mainly excrete urea and are called ureotelic animals.
• Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys.
• Some amount of urea may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity.
• Terrestrial adaptation necessitated the production of lesser toxic nitrogenous wastes like urea and uric acid for conservation of water.
Uricotelic animals.
• Reptiles, birds, land snails and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals.
— To be continued
