The excretory organ of Fishes, Amphibians, Birds and Man is the "kidney".

reptiles, birds, and mammals. The principle focus is on the role of the kidneys in this process. Although the basic elements of renal function are similar in the three classes, birds and mammals are set apart from reptiles in that the kidneys of these species have the ability to produce urines that are hyperosmotic to plasma. Reptiles and birds are set apart from mammals by the fact that these two groups excrete nitrogen as uric acid and not urea as do mammals. Reptiles and birds are further set apart from mammals in that the kidneys of these two groups are not the sole organs that function to regulate the composition of the extracellular fluid. In addition to having functional salt glands, the lower gastrointestinal tracts of reptiles and birds function in concert with the kidneys in the maintenance of homeostasis. There is a much greater range in body mass among mammals than in the other two groups. This has necessitated that the kidneys of mammals change size, shape, and internal organization to be able to carry out their homeostatic function. The kidneys of reptiles and birds do not follow a similar pattern. It would appear that no one group has the advantage over the other with respect to

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Fishes, amphibians, birds, man All Have Kidney as Excretory Organ

Fishes, amphibians, birds and man all have kidney as the excretory organ. The excretory system is responsible for the elimination of wastes produced by homeostasis. There are several parts of the body that are involved in this process, such as sweat glands, the liver, the lungs and the kidney system. The kidneys excrete a variety of waste products produced by metabolism into the urine. These include the nitrogenous wastes urea, from protein catabolism, and uric acid, from nucleic acid metabolism.