It serves to maintain the lonic and osmotic equilberium that is necewary for fan

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It serves to maintain the lonic and osmotic equilberium that is necewary for fanctions. The body system that regulates the removal of wastes is the eu (or urinary) system, and its main organs are the kidneys and the bladder, Asthe b processes proteins during into soluble metabolites. The kidneys can filher out thevemeabis eliminate them from the body with other squeous waste, maintainings the water and pH balance of the internal environment. Waste nitrogen is produced in different forms for different groups o (Figure 2). Bony fishes produce ammonia, mammals and cartilagimous hishes skates, rays) produce ures, and most birds produce uric acid as nitrogmous wase proteins amino acids amino groups rays, aquatic replies celular fuels nucleic acids Figure 2 Nitrogenous wastes excreted by different animal groups As you learned in Chapter 1, the building blocks of proteins are amino acids Aa amino acid contains a nitrogen atom bonded to two hydrogen atoms, called an amino group. In the process of deamination, which occurs in the liver, the amino group removed from each amino acid that comes from the breakdown of a protein. The amino group is then converted to ammonia. The rest of the amino acid, which mostly carbon and hydrogen, is oxidized to produce energy Ammonia, NH, the by-product of deamination, is a highly toxic substance. A buildup of as little as 0.005 mg/L can kill a human. It can be transported and secnted only in very dilute solutions. Animals with an abundant supply of water (sucha bony fish and marine invertebrates) are able to secrete ammonia direcly from the body in this very dilute form. In mammals, some reptiles, and most ampbiban the liver combines ammonia with HcO, to create urea, a very with 0.001 % the toxicity of ammonia. In fact, 33 mg of urea can be dissolved in jt 100 mL of blood with no toxic effects. Although the chemical reactions that prodace urea require more energy than the reactions that produce ammonia, urea can be eliminated from the body with less water, allowing terrestrial animals to maintain their water balance. solable substance Other animals conserve water even more efficiently. For example, birds and some terrestrial invertebrates produce uric acid as their nitrogenous waste prodact Uhe urine is concentrated in its final stages, the uric acid forms crystals that are espeled bird drop- acid is not toxic, but its key feature for these smaller animals is its low solubility. As pings is uric acid crystals.) Most animals are able to form all three of these nitrogen conservation, toxicity, and energy requirements, You will learn about the excetor UNIT TASK BOOKMARK from the body with a minimal amount of water. (The white substance in waier You may want to consider thermoregulation (Section 9.3) or water balance (Section 9.4) as a factor for your Unit Task on page 566. system and the functions of its organs in humans in Section 9,5 compounds, but the primary method of excretion depends on a balance umong

Explanation / Answer

excretion is a process that eliminates any waste products from the body that are toxic. One such products are nitrogen containing compounds like ammonia, urea and uric acid. Ammonia is product after catabolic degradation of amino acids in a process called deamination of the amino acids. Ammonia is highly toxic to the living organisms. Different organism excrete different by products depending on their physioogy and habitat. Organisms which live in water have abundant water for excretion of direct ammonia. the reason why huge volumes of water are required to excrete ammonia so as to dilute its toxicity. Humans, however like other terrestrial organisms cannot bare to loose great amounts of water to ecrete ammonia, which is why ammonia is converted into urea through urea cycle by addition of bicarbonate to ammonia in liver. Urea is less toxic and thus require less water to dilute its toxicity. Even though the process requires energy, the expense is necessary to prevent water loss from the body. evolutionary some other vertebrate like birds and certain invertebrates excrete uric acid which is even less toxic and urine in such organism is in the form of light dilute paste requiring minimal water for excretion.

These nitrogenous compounds then require a mechanism to be excreted. in lower organisms this is done by simple diffusion whereas some have malphigian tubules and prilimnary kidneys. Humans have two kidneys that filter the blood to remove urea and add it to urine which is then stored in urinary bladder. They also maintain water balance of the body by selectively re-absorbing water and electrolytes. When urinary bladder fill upto a volume (300-400ml) micturition is inititated and the urine is passed through urethra. Kidney can be divided into regions medulla and cortex. the functional unit of kidney is a nephron which contains a bouman's capsule which aid in blood filtration and a series of convoluted tubules which conduct the urine and reabsorb water and/or secrete urea, the urine from these tubules is collected in the collecting tubules in the renal pelvis which then empties into the urinary bladder.

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