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Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea (by liver), which is much less toxic, particularly less basic. This urea is a major component of the dry weight of urine. Most reptiles, birds, insects, and snails excrete uric acid solely as nitrogenous waste.
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. [3] Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion.
In animals, the main excretory products are carbon dioxide, ammonia (in ammoniotelics), urea (in ureotelics), uric acid (in uricotelics), guanine (in Arachnida), and creatine. The liver and kidneys clear many substances from the blood (for example, in renal excretion), and the cleared substances are then excreted from the body in the urine and ...
The urea cycle is essential to these organisms, because if the nitrogen or ammonia is not eliminated from the organism it can be very detrimental. [5] In species including birds and most insects, the ammonia is converted into uric acid or its urate salt, which is excreted in solid form. Further, the urea cycle consumes acidic waste carbon ...
Because ammonia is toxic, it is excreted immediately by fish, converted into uric acid by birds, and converted into urea by mammals. [47] Ammonia (NH 3) is a common byproduct of the metabolism of nitrogenous compounds. Ammonia is smaller, more volatile, and more mobile than urea.
Urine after four months of storage (note the color and turbidity change compared to fresh human urine). During storage, the urea in urine is rapidly hydrolyzed by urease, creating ammonia. Collected urine can be used as a fertilizer. Fresh human urine after excretion
Only the organs specifically used for the excretion are considered a part of the excretory system. In the narrow sense, the term refers to the urinary system . However, as excretion involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.
Ammonia is toxic to the human system, and enzymes convert it to urea or uric acid by addition of carbon dioxide molecules (which is not considered a deamination process) in the urea cycle, which also takes place in the liver. Urea and uric acid can safely diffuse into the blood and then be excreted in urine.