Carbon dioxide bicarbonate buffer

The pH-buffering of extracellular fluid depends in part on the carbon dioxide/ bicarbonate equilibrium so that the intake of sodium bicarbonate is followed by a brief alkalosis and an increased excretion of sodium carbonate in the urine. Depending on its carbonate concentration, the pH of the urine may rise to 8.07. Large doses (80—100 g/day) of sodium bicarbonate were needed if the pH of stomach contents was to be maintained at 4 or over in patients with duodenal ulcers8. Oxidation of organic anions in the body to carbon dioxide and water permits the use of sodium citrate, lactate or tartrate instead of sodium bicarbonate. In an analogous manner the ingestion of ammonium chloride induces a brief acidosis as a result of the metabolic conversion of ammonia to urea and lowers the pH of the urine. 

As described in Chapter 2, the usual normal buffer system in culture media is the carbon dioxide-bicarbonate system, analogous to that in the blood. Modifications in the medium pH produce changes to the intracellular pH value, with modifications to enzyme activities. 

The CO2 in the blood also participates in the carbonic acid-bicarbonate buffer equilibrium. Carbon dioxide reacts with water in the blood to form carbonic acid ... 

There are also several mechanisms by which our body maintains the pH around 7.4. Some of these mechanisms use simple standard chemistry, some are more complex. These mechanisms are (i) the carbonic acid-bicarbonate buffer system, (ii) the protein buffer system, and (iii) the phosphate buffer system. Apart from these buffers, the pH of our body is also maintained by exhalation of carbon dioxide, elimination of hydrogen ions via the kidneys, etc. 

The major buffer system used to control blood pH is the carbonic acid—bicarbonate buffer system. Carbonic acid (H2CO3) and bicarbonate ion (HCO3 ) are a conjugate acid ase pair. In addition, carbonic acid decomposes into carbon dioxide gas and vrater The important equilibria in this buffer system are... 

Cosmetics and Toiletries. Citric acid and bicarbonate are used in effervescent type denture cleansers to provide agitation by reacting to form carbon dioxide gas. Citric acid is added to cosmetic formulations to adjust the pH, act as a buffer, and chelate metal ions preventing formulation discoloration and decomposition (213—218). 

Sodium bicarbonate is used as a leavening in breads, as a stomach antacid, as a buffering agent to adjust the acidity or alkalinity of a product, as a mild abrasive in toothpaste, and as an odor absorber. Sodium bicarbonate reacts with acids to release carbon dioxide gas. 

Figure 6-9. The Bohr effect. Carbon dioxide generated in peripheral tissues combines with water to form carbonic acid, which dissociates into protons and bicarbonate ions. Deoxyhemoglobin acts as a buffer by binding protons and delivering them to the lungs. In the lungs, the uptake of oxygen by hemoglobin releases protons that combine with bicarbonate ion, forming carbonic acid, which when dehydrated by carbonic anhydrase becomes carbon dioxide, which then is exhaled.

Acid-base reactions of buffers act either to add or to remove hydrogen ions to or from the solution so as to maintain a nearly constant equilibrium concentration of H+. For example, carbon dioxide acts as a buffer when it dissolves in water to form carbonic acid, which dissociates to carbonate and bicarbonate ions ... 

Fermentation of D-xylose by Escherichia coli at pH 5.5 (in bicarbonate buffer) gives more than one mole of lactic acid per mole because of fixation of carbon dioxide by the two-carbon fragment,198(a> an observation that may have an important bearing on theories of photosynthetic fixation of carbon dioxide.198[Pg.223]

Acid-base disorders are caused by disturbances in hydrogen ion (H+) homeostasis, which is ordinarily maintained by extracellular buffering, renal regulation of hydrogen ion and bicarbonate, and ventilatory regulation of carbon dioxide (C02) elimination. 

Dissolved carbon dioxide produces carbonic acid, which ionizes to bicarbonate and carbonate ions, the reactions for which are shown in Figure 5.2 (equations 1-3). This reaction sequence is extremely important because bicarbonate is a counterion to many cations, is active in buffering the soil solution, and is involved either directly or indirectly in many soil chemical reactions. Bicarbonates are generally more soluble than carbonates, which are generally insoluble. Adding acid to carbonates or bicarbonates results in the release of carbon dioxide and the formation of the salt of the acid cation. The acid is thus neutralized. 

Cholinesterase 3.1.1.8 Acetylcholine Acetic acid Carbon dioxide release from bicarbonate buffer... 

Tissue culture, more frequently used as cell culture, enables animal and plant cells to be cultured in large numbers by techniques comparable to those used in microbiology but, because of the fragile nature of the cells, does require special cultural conditions. The culture media used must supply all the essential factors for growth, such as a wide range of amino acids, nucleotides, enzyme co-factors as well as indeterminate factors that can only be supplied in special products, e.g. foetal bovine serum. The environmental conditions must be carefully controlled, particularly pH, and this is frequently maintained by culturing in a bicarbonate buffer system and a carbon dioxide saturated atmosphere. 

By the late 1920s quantitative micro-determination of oxygen uptake had been developed in Warburg s laboratory in Berlin based on a manometric technique introduced by Barcroft and Haldane (1902). With this equipment evolution of carbon dioxide or uptake of oxygen could be monitored Carbon dioxide produced in respiration was absorbed by potassium hydroxide. If bicarbonate buffer was used, acid production caused carbon dioxide to be released. Krebs and others from... 

The reactions in Table 13.8 show that carbon dioxide is a common product in many neutralization reactions. This is clearly displayed when a drop of vinegar (acetic acid) is added to baking soda (sodium bicarbonate). Some aspirin includes an antacid in their formulation to neutralize some of the acidity imparted by the aspirin (acetylsalicylic acid). These are commonly referred to as buffered aspirins. 

The excessive amount of bicarbonate in the blood means that blood has a much greater capacity to neutralize acids. Many acids accumulate in the blood during strenuous activity, for example lactic acid. Excretion of bicarbonate through the kidneys and the removal of carbon dioxide through respiration also regulate the carbonic acid/ bicarbonate blood buffer. 

The human body is a remarkable machine. It relies on a variety of safeguards to keep blood pH constant. Our blood constitutes a buffer system — meaning, it has components that can react with excess base or excess acid. Carbon dioxide, which is produced by the metabolism of food, dissolves in blood to produce carbonic acid, and carbonic acid can neutralize any excess base. The bicarbonate ion, also present in blood, will promptly take care of any surplus acid. The level of carbon dioxide in the blood adjusts to a body s rate of respiration. If blood pH drops — which actually means that the blood has... 

A third problem with the mitochondrial theory of biomineralization is that many mineralized tissues contain carbonate rather than phosphate. Since bicarbonate ions do not pass across mitochondrial membranes with any ease, it has now been shown that in phosphate-free buffers, calcium will enter mitochondria if dissolved carbon dioxide is available. It appears that some mitochondria possess carbonic an-hydrase activity on the inner membrane or in the mitochondrial matrix and are thus able to synthesize bicarbonate within the organelle. In such cases, inhibitors of carbonic anhydrase block the accumulation of calcium and carbonate ions622) since crystals of calcite have been identified in the mitochondria of earthworms calci-ferous glands623. These cells freqently showed spherical granules in the cytoplasm and lumen of the glands during phases of mineral secretion and it was suggested that they were aspects of cellular breakdown which occurred at these times. 

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