The excretory system exists in all living creatures in order to facilitate the removal of nitrogen rich minerals, as well as additional waste products. The excretion process also serves to normalize water and ions in the body. Birds and reptiles differ in many ways, yet the function of the excretory system of species is actually remarkably similar in purpose.
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Food consumption of some sort is necessary for the survival of both birds and reptiles. As food is ingested, the bodies of each of these species begin to undergo the metabolic process. According to the University of Cincinnati, metabolism serves as a means to break down protein and nucleic acid, both of which contain nitrogen. Some of the nitrogen is used by the body, but the majority must be excreted as a waste product.
According to the University of Cincinnati, the main way that both birds and reptiles rid their bodies of the surplus of nitrogen is by turning nitrogen into uric acid or ammonia. Converting the nitrogen is beneficial to birds and reptiles because their bodies are then able to excrete these substances with a minimal loss of water. In the case of cold-blooded animals, as well as many birds, that must be preserved as much as possible.
According to the Biology Web, when nitrogen forms in the body, it eventually becomes a toxic element. The excretory system allows the nitrogen to be excreted by the body before it begins to affect the pH of bodily fluids. In many animals, salt must also be excreted. Many birds and reptiles inhabit areas close to the sea and, as a result, they ingest large quantities of salt. The bodies of these animals excrete the excess salt in the form of a salt solution through nasal salt glands.
According to New World Encyclopedia, reptiles use two small kidneys as tools for excretion. The kidneys serve to filter the nitrogen from the animal's bloodstream, then turn it into waste. The nitrogen then exits the body in dry form as uric acid crystals along with the feces. According to Stanford University, the kidneys in a bird also function as a means to remove nitrogen from the blood. The white substance found in bird droppings is actually uric acid, which is not water soluble. In both reptiles and birds, eliminating the nitrogen requires that the body exerts a great deal of energy. Both species are able to efficiently remove the nitrogen while losing very little water in the waste product.
The excretory system of birds and reptiles effectively removes nitrogen from their bodies, and this system allows for the preservation of water. According to Back Yard Nature, when mammals excrete nitrogen, it is the form of urea, which dissolves very easily in water. In animals whose bodies are not water-based, using uric acid as a means for excretion allows for their survival with minimal water ingestion.