maria - Animal Excretion and Osmoregulation in Maintaining...

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Animal Excretion and Osmoregulation in Maintaining Homeostasis Maria Gumina Dr. Rivers Comparative Physiology February 26, 2004
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Homeostasis is, “a condition of relative internal stability maintained by physiological control systems” (Burggren et. al., G11). Without this balance between internal and external environment survival would be extremely difficult. The animals that live on Earth today utilize the diverse environments that they encounter and they have evolved adaptations to maintain homeostasis. One physiological problem that arises within homeostasis is osmoregulation, or simply maintaining a level of a constant osmotic pressure within the body. Cell survival depends on maintaining the appropriate amounts of water and the correct concentrations of solutes. A process that accompanies osmoregulation is excretion. Excretion is a system of eliminating metabolic waste products. This process works alongside of osmoregulation due to the fact that excretion is a means of regulating water and ion concentrations within bodily fluids. At some point in all animals’ evolutionary history these processes of excretion and osmoregulation were physiological problems that they have overcome. They were able to adapt and expend as little energy necessary to maintain life. It has been said that, “The evolution of mechanisms of osmoregulation has allowed organisms to penetrate into new and different osmotic environments” (Burggren et. al., 578). This paper will examine these “mechanisms of osmoregulation” that have adapted in invertebrates and vertebrates, specifically in marine environments versus terrestrial environments. In a quick overview of excretion: nitrogen accumulates in animals due to the deamination of amino acids. Some of the amino groups that are released are recycled and used again, while others must be removed. Those that are no longer needed, “must be dissolved in water and excreted to avoid a toxic rise in the plasma concentration of
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nitrogenous wastes” (Burggren et. al., 625). In most animals this excess nitrogen is expelled as ammonia, urea, or uric acid. It is the diverse properties of these, “nitrogenous excretory compounds that affects how animals have evolved” (Burggren et. al, 625). Most aquatic invertebrates in comparison to vertebrates do not have intricate maintenance of excretion and osmoregulation due to the fact that they live in an environment of water. Therefore, it is not necessary for these invertebrates to develop a complex network of excretory organs. Freshwater invertebrates are mainly hyperosomotic to their surroundings. Therefore, they must prevent excess water absorption and minimize loss of salts. Many have well adapted to this. In comparison we will look at marine invertebrates. An example of a marine invertebrate is the starfish, Astropecten armatus . These animals belong to the phylum echinodermata and are osmoconformers. Dissolved nitrogen waste takes the form of ammonia and is their major product of excretion. The starfish is
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maria - Animal Excretion and Osmoregulation in Maintaining...

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