Nitrogenous waste excretion

Walsh, P. J., Wang, Y., Campbell, C. E., De Boeck, G., and Wood, C. M. (2001). Patterns of nitrogenous waste excretion and giU urea transporter mRJSTA expression in several species of marine fish. Mar. Biol. 139, 839-844. 

Metabolism of nitrogen in a patient with a deficiency in the urea cycle enzyme carbamoyl phosphate synthetase I. Treatment with phenylbutyrate converts nitrogenous waste to a form that can be excreted. 

Figure 12.1 Schematic of a single nephron, the functional unit of the kidney. Microsolutes are filtered from blood cells in Bowman s capsules. As the filtrate passes towards the collection tubule most of the microsolutes and water are reabsorbed by a type of facilitated transport process. The fluid finally entering the collecting tubule contains the nitrogenous wastes from the body and is excreted as urine. There are about 1 million nephrons in the normal kidney [1]...

While the complete oxidations of fats and carbohydrates yield C02 + H20, the complete oxidation of amino acids yields C02 + H20 and as well as ammonia. Three fates of this so-called nitrogen waste product are common in animals it can be excreted into the outside medium (ammonotelism, which is common in many aquatic animals) it can be excreted as uric acid (uricotely, common in reptiles and birds) or, it can be excreted as urea (common... 

The kidneys excrete a variety of waste products produced by metabolism, including the nitrogenous wastes urea (from protein catabolism) and uric acid (from nucleic acid metabolism). The kidneys also excrete many drugs or their metabolites, in particular those that are hydrophilic, have a small volume of distribution and a low degree of protein binding. 

From the symptoms and examination of blood and urine, a diagnosis of chronic renal failure is made. Unfortunately, considerable kidney damage can occur, often over a period of years, before the patient notices the symptoms associated with chronic renal failure. As the amount of functioning kidney tissue decreases, blood electrolytes begin to change. At the same time, the ability of the kidney to excrete nitrogenous waste decreases and urea concentration in the blood rises (uraemia). The patient may remain symptom-free until the concentration of urea rises sufficiently to cause the nausea and vomiting Kevin has recently experienced. 

Animals in general are not able to take up inorganic nitrogen directly (Muscatine etal., 1979), and usuaUy excrete reduced nitrogenous wastes into the surrounding water (Rahavet (j/., 1989). Algal-invertebrate symbioses of coral reefs are an exception to this... 

C. The kidney excretes nitrogenous waste products, including urea, ammonia, creatinine, and uric acid. If the kidneys fail, these waste products will not be excreted into the urine. 

David HE, Peter MP, Keith PC (2005) The multifunctional fish gill dominant site of gas exchange, osmoregulation, acid—base regulation, and excretion of nitrogenous waste. Physiol Rev 85 97-177... 

A.3.2 The liver is an organ with many functions and the very definition of its metabolic state can be very complicated. Some of the major functions of the liver are to produce enzymes to break down fats and proteins and the conversion of sugars into proteins and vice versa. The liver makes most amino acids and will process nitrogen waste to make urea, which is excreted in the urine. The liver detoxifies many materials that are ingested and will metabolize drugs and alcohol. It stores certain vitamins, breaks down hemoglobin (from red blood cells) and maintains the level of glucose in the blood. It also makes 80% of the cholesterol in the body. 

After a discussion of nitrogen fixation, the essential features of amino acid biosynthesis are described. This is followed by descriptions of the biosynthesis of selected nitrogen-containing molecules. A special emphasis is placed on the anabolic pathways of the nucleotides. In the following chapter (Chapter 15) the flow of nitrogen atoms is traced through several catabolic pathways to the nitrogenous waste products excreted by animals. 

In nature, there are many pathways for incorporation of ammonia into soil. Natural sources include microbial decomposition of dead plants and animals, and hydrolysis or breakdown of urea and nitrogenous waste products in animal excretions. Several species of microorganisms can produce ammonia by the fixation of dinitrogen, and these organisms are widely dispersed throughout the soil (Atlas and Bartha 1998 Crutzen 1983). While several species of microbes can perform nitrogen fixation, this capability would not be one that is considered common for most microorganisms. 

The carbonic anhydrase inhibitors cause metabolic acidosis and urinary alkalosis. Patients with severe impairment of liver function are unahle to synthesize urea efficiently and become dependent on renal excretion of ammonium ion to rid the body of nitrogenous wastes. However, in alkaline urine the ammonium ion is rapidly converted to ammonia gas. which is veiy rapidly reabsorbed. Hyperammonemia results, with severe neurologic consequences. The answer is (A). 

Urea is formed in the body from ammonia that comes from deamination of amino acids it permeates throngh the entire body except the brain. Excreted urea can be used as a nitrogen source by microbes, plants, and animals. Creatinine is the nitrogenous waste product of muscle creatine phosphorylated creatine (also called phosphageri) is an energy source alternative to ATP (see Section 3.9). Diadrast is the commercial name for iodopyracet, an iodinated dye used to determine kidney function it has the property that a very high proportion is filtered and excreted from the kidney in a very short time. Hippurate is a salt of hippuric acid, and is used as a test of liver function. 

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