Carbonic acid buffer system

The bicarbonate-carbonic acid buffer system plays a major role in regulating the pH of fluids in tissue spaces outside blood vessels. This fluid, commonly referred to as interstitial fluid and separated from plasma by the membrane barrier known as the capillary endothelium, primarily... 

Since biological systems are dynamic, with many different processes taking place and many different substances present, buffers are necessary to prevent the kind of wide variation of pH that can inhibit proper enzyme catalysis. Thus, a proper pH aids in regulating the reaction rates associated with certain enzymes and maintaining them at levels appropriate for their particular functions. Two important biological buffers are the phosphate buffer system that regulates pH for the fluid inside cells and the carbonic acid buffer system that regulates pH for blood plasma. The chemical equations for these buffers are shown below for an aqueous solution. 

Phosphate buffer system) (Carbonic acid buffer system)... 

The solubihty of proteins in blood requires a pH in the range of 7.35 to 7.45. The bicarbonate-carbonic acid buffer system of blood (HCOj +... 

An average rate of metabolic activity produces roughly 22,000 mEq acid per day. If all of this acid were dissolved at one time in unbuffered body fluids, their pH would be less than 1. However, the pH of the blood is normally maintained between 7.36 and 7.44, and intracellular pH at approximately 7.1 (between 6.9 and 7.4). The widest range of extracellular pH over which the metabolic functions of the liver, the beating of the heart, and conduction of neural impulses can be maintained is 6.8 to 7.8. Thus, until the acid produced from metabolism can be excreted as CO2 in expired air and as ions in the urine, it needs to be buffered in the body fluids. The major buffer systems in the body are the bicarbonate-carbonic acid buffer system, which operates principally in extracellular fluid the hemoglobin buffer system in red blood cells the phosphate buffer system in all types of cells and the protein buffer system of cells and plasma. 

One very important buffer solution is human blood An equilibrium between carbonic acid (H2CO3) and its conjugate base bicarbonate (HCOsi helps blood to maintain a relatively constant pH of around 7.4. The carbonic acid buffer system is created by carbon dioxide (CO2) dissolved in blood carbon dioxide reacts with water (H2O) to form carbonic acid. Since the amount of carbon dioxide in the blood depends on the rate at which you breathe, your blood pH is influenced by your breathing rate. Your body can... 

Seawater is a weakly basic solution, with pH values typically between 8.0 and 8.3. This pH range is maintained through a carbonic acid buffer system similar to the one in blood (see Equation 17.10). 

Just as in our bodies, the carbonic acid buffer system can be perturbed by removing or adding C02(g). The concentration of dissolved CXJ2 the ocean is sensitive to changes in atmospheric CO2 levels. As discussed in Chapter 18, the atmospheric CO2 concentration has risen by approximately 30% over the past three centuries to the present level of 386 ppm. Human activity has played a prominent role in this increase. Scientists estimate that one-third to one-half of the CO2 emissions resulting from human activity have been absorbed by Earth s oceans. While this absorption helps miti-... 

In the human body, carbon dioxide provides the buffer. This is called the carbonic acid-hydrogen carbonate ion buffer system. This buffer system maintains the body s blood pH within acceptable levels. The main threat to the bloods pH is excess hydrogen ions produced by various chemical reactions in the body. When hydrogen ions are produced, hydrogen carbonate ions in the blood pick them up and convert them to carbonic acid ... 

C. The carbonic acid-bicarbonate system is the most important buffer of the... 

Buffer substances which occur in nature include phosphates, carbonates, and ammonium salts in the earth, proteins ol plant and animal (issues, and the carbonic-acid-bicaihonatc system in blood. Sec also Acid-Base Regulation (Blood). 

Buffers stabilize a solution at a certain pH. This depends on the nature of the buffer and its concentration. For example, the carbonic acid-bicarbonate system has a pH of 6.37 when the two ingredients are at equimolar concentration. A change in the concentration of the carbonic acid relative to its conjugate base can shift the pH of the buffer. The Henderson-Hasselbalch equation below gives the relationship between pH and concentration. 

HA] is the concentration of the acid and [A-] is the concentration of the conjugate base. The pKa of the carbonic acid-bicarbonate system is 6.37. When equimolar conditions exist, then [HA] = [A ]. In this case, the second term in the Henderson-Hasselbalch equation is zero. This is so because [A ]/[HA] = 1, and the log 1 = 0. Thus at equimolar concentration of the acid-conjugate base, the pH of the buffer equals the pKa in the carbonic acid-bicarbonate system this is 6.37. If, however, we have ten times more bicarbonate than carbonic acid, [A ]/[HA] = 10, then log 10 = 1 and the pH of the buffer will be... 

The buffer systems of the blood (mainly the bicarbonate/ carbonic acid buffer) minimize changes in pH. In acidoses, the bicarbonate concentration decreases to give a ratio of cHC03/cdC02 of <20 1. The respiratory compensatory mechanism responds to correct the ratio with increased rate and depth of respiration to eliminate CO2. Table 46-3 depicts expected compensation in both acidoses and alkaloses and corresponding laboratory values. 

Thus, the physiologic regulation of both PCO2 and [HCO/] permit the carbonic acid/bicarbonate system to provide more effective buffering of the extracellular fluids than could be achieved on the basis of chemical buffering alone. 

The important buffer system of blood plasma is the bicarbonate/carbonic acid couple ... 

Under the conditions of temperature and ionic strength prevailing in mammalian body fluids, the equilibrium for this reaction lies far to the left, such that about 500 CO2 molecules are present in solution for every molecule of H2CO3. Because dissolved CO2 and H2CO3 are in equilibrium, the proper expression for H2CO3 availability is [C02(d)] + [H2CO3], the so-called total carbonic acid pool, consisting primarily of C02(d). The overall equilibrium for the bicarbonate buffer system then is... 

With regard to the buffer system, an extensive range of amino acid derivatives applied in combination with an alkali have been claimed [99]. From this extensive list, primary preference is given to N,N-bis(hydroxyethyl)glycine (12.24) in combination with sodium hydroxide. However, N,N-dimethylglycine, N-methylglycine and N-methylalanine are also listed as preferred compounds, whilst other possible alkalis include sodium carbonate,... 

Buffering refers to the ability of a solution to resist change in pH after the addition of a strong acid or base. The body s principal buffer system is the carbonic acid/bicarbonate (H2C03/HC03 ) system. 

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. 

The Henderson-Hasselbach equation allows the ratio of ionized un-ionized compound to be found if the pH and pKa are known. Consider carbonic acid (H2CO3) bicarbonate (HC03 ) buffer system... 

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