Ammonia Secretion

There seem to be two problems NH3 is non-charged and mobile and easily crosses plasma membranes. When charged, however, in the form of NH41+, it penetrates cells with difficulty and tends to accumulate in biological systems. As a proton remover, therefore, ammonia secretion is a poor mechanism. It may temporarily trap the protons, and therefore facilitates the reaction as shown in Eq. (7), but the products tend to remain at the site of cacification. 

Formation Secretion of Ammonia Maintains Acid-Base Balance... 

During conditions of acidosis, hydrogen ions are excreted (secreted) by the kidney to maintain the normal pH of the blood. These ions are buffered in urine by ammonia, in the reaction... 

Since these are fundamentally important processes, the transport of protons into the glomerular filtrate and the transport of ammonia can be considered as secretions rather than excretions. 

As indicated above, one function of the kidney is to maintain the pH of the blood by excreting (secreting) protons into the glomerular filtrate during acidosis. In order to buffer these protons in the glomerular filtrate, ammonia is also excreted. The buffering occurs as follows ... 

Ammonia buffers protons in the tubules of the kidney to prevent formation of an acidic urine, when the kidney excretes (secretes) protons to control the pH of the blood. 

An important buffer in the urine is the hydrogen phosphate/dihydrogen phosphate system (HP04 /H2P04 ). In addition, ammonia also makes a vital contribution to buffering the secreted protons. 

Volatile irritants such as ammonia and chlorine initially cause constriction of the bronchioles. These two gases are water soluble, are absorbed in the aqueous secretions of the upper airways of the respiratory system, and may not cause permanent damage. Irritant damage may however lead to changes in permeability and edema, the accumulation of fluid. Some irritants such as arsenic compounds cause bronchitis. 

SHELLAC. A secretion or excretion of the lac insect, Coccus lacca, found in the forests of Assam and Siam. Freed from wood it is called seed lac." It is soluble in alkaline solutions such as ammonia, sodium borate, sodium carbonate and sodium hydroxide, and also in various organic chemicals. When dissolved in acetone or alcohol, shellac yields the familiar shellac varnish of superior gloss and hardness. Orange shellac is bleached with sodium hypochlorite solution to form white shellac. See also Paints and Coatings. 

Ammonia is also the major nitrogenous end product in some of the simpler aquatic and marine animal forms, such as protozoa, nematodes, and even bony fishes, aquatic amphibia, and amphibian larvae. Such animals are called am-monotelic. But in many animals, NH3 is toxic, and its removal by simple diffusion is difficult. Thus, in terrestrial snails and amphibia, as well as in other animals living in environments in which water is limited, urea is the principal end product (fig. 22.6). Urea formation also helps to maintain osmotic balance with seawater in cartilagenous fishes. In such animals, most of the urea secreted by the kidney glomerulus is reabsorbed by the tubules. Indeed, the amount of nitrogen excreted by the kidneys of fishes is small com-... 

Urea cycle. A metabolic pathway in the liver that leads to the synthesis of urea from amino groups and C02. The function of the pathway is to convert the ammonia resulting from catabolism to a nontoxic form, which is subsequently secreted. 

DuPont Co, Wilmington, Del has been manufg several brands of ammonia dynamites, such as "DuPont Extra , "Red Cross Extra , "Red Cross Blasting FR etc. Some of their props are given in Ref 8, but their compn seems to be a trade secret... 

The manufacturers of tobacco products add fillers, flavor enhancers, preservatives, and other additives to make the product more desirable to consumers, especially low-tar brands. Each company s list of additives was a closely guarded trade secret until 1984, when the lists were submitted to the government. The public was barred from seeing the lists until 1994. The initial list contained 700 potential additives, of which 13 are not allowed in food. One additive, ammonia, may be included to boost the absorption of nicotine and enhance the addictive kick. Sweeteners and chocolate may help make cigarettes more attractive to children and first-time users. 

On the other hand, Cruz et al. (2000) reported that 28 mM lactate reduced the growth of a BHK cell line by 50%, and that lactate was consumed at concentrations above 30 mM. Increased concentrations of lactate reduced cell growth and specific ammonia production but increased specific glutamine and glucose consumption. The effect of lactate was at least partially due to an increase of osmolarity. An increase in lactate from 0 to 60 mM induced a 40% reduction in specific productivity of a recombinant fusion protein secreted by the BHK cells in both stationary and stirred cultures. 

Ammonia (NH3) and the ammonium ion (NH4"1") are highly toxic to mammalian cells. In vivo, ammonium is secreted by the cells and transported to the mitochondria of hepatocytes, where it is converted into urea via the urea cycle. Urea production occurs almost exclusively in the liver and is the fate of most of the ammonium channeled there. The urea passes into the bloodstream and thus to the kidneys and is excreted into the urine. Mammalian cells in culture secrete ammonium into the culture medium, where its concentration increases gradually because there is no ammonium recycling pathway (Newland et al., 1990). 

The predominant buffers in the urine are phosphate (HP042 ) and ammonia (NH3). Phosphate is freely filtered by the glomerulus and passes down the tubule where it combines with H+ to form Hd Oy. Hydrogen ions are secreted in exchange for sodium ions the energy for this exchange comes from the sodium-potassium ATPase that maintains the concentration gradient for sodium. 

Most doctors use the plasma concentrations of creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease. Protein and amino acid catabolism results in the production of ammonia, which in turn is converted via the urea cycle into urea, which is then excreted via the kidneys. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little to no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. 

Ostwald The basis of the modem family of processes for making nitric acid by the oxidation of ammonia over a platinum catalyst. Named after the eminent German physical chemist Friedrich Wilhelm Ostwald (1853 to 1932). His invention was patented in the United States in 1902, but the patent was not granted in Germany, where the process had to be operated in secret. Ostwald received the Nobel Prize for this work in 1909. 

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