Blood plasma buffer systems

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

The pH value is kept constant by buffer systems that cushion minor disturbances in the acid-base balance (C). In the longer term, the decisive aspect is maintaining a balanced equilibrium between H" production and uptake and H" release. If the blood s buffering capacity is not suf cient, or if the acid-base balance is not in equilibrium—e.g., in kidney disease or during hypoventilation or hyperventilation-shifts in the plasma pH value can occur. A reduction by more than 0.03 units is known as acidosis, and an increase is called alkalosis. 

The second dissociation step in phosphate (H2P04/HP04 ) also contributes to the buffering capacity of the blood plasma. Although the pKa value of this system is nearly optimal, its contribution remains small due to the low total concentration of phosphate in the blood (around 1 mM). 

Blood plasma is buffered in part by the bicarbonate system, consisting of carbonic acid (H2C03) as proton donor and bicarbonate (HCO ) as proton acceptor ... 

Figure 3.3 Relationships among pC02, pH, and [HC03 ] for the extracellular bicar-bonate-COz buffer system. "True plasma" means that the plasma was separated from blood cells under anaerobic conditions to preserve its C02 content. The normal buffer line provides a standard reference for the relationship amongpC02, [HC03 ], and pH. Its slope depends on blood hemoglobin content.

Three common examples of buffers. Many medications are buffered to minimize digestive upset. Most body fluids, including blood plasma, contain very efficient namral buffer systems. Buffer capsules are used in laboratories to prepare solutions of specified pH. 

The blood, for example, is protected by two important buffer systems the hemoglobin system and the bicarbonate system, which stabilize its pH between 7.37 and 7.43. The bicarbonate system is the most important buffer for plasma and interstitial fluids. Neutralizing the skin with sodium bicarbonate is the most natural method. 

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... 

As discussed in Chapter 1, at a blood pH of 7.4, the ratio of [HCO3 ] to [H2CO3] is 20 1 and the system s buffering capacity can neutralize a large amount of acid. The system is independently regulated by the kidneys, which control the plasma HCOj level, and by the respiratory rate, which regulates the Pco2- Protein and phosphate buffer systems also operate in plasma and erythrocytes. Proteins are especially important buffers in the intracellular fluid. The hydroxyapatite of bone also acts as a buffer. 

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. 

C02 (total) Blood plasma GD UV—Vis 10—50 mmol I.1 Flow injection system original implementation of gas diffusion in flow injection analysis buffered cresol-red indicator solution as the acceptor stream [265]... 

The pH of blood plasma is maintained at about 7.40 by several buffer systems, the most important of which is the HCO3/H2CO3 system. In the erythrocyte, where the pH is 7.25, the principal buffer systems are HCO3/H2CO3 and hemoglobin. The hemoglobin molecule is a complex protein molecule (molar mass 65,000 g) that contains a number of ionizable protons. As a very rough approximation, we can treat it as a monoprotic acid of the form HHb ... 

The pH of blood plasma is 7.40. Assuming the principal buffer system is HC0 /H2C03, calculate the ratio [HC0J]/[H2C03]. Is this buffer more effective against an added acid or an added base ... 

In animals with lungs, the bicarbonate buffer system is an effective physiological buffer near pH 7.4, because the H2CO3 of blood plasma is in equilibrium with a large reserve capacity of C02(g) in the air space of the lungs. This buffer system involves three reversible equilibria between gaseous CO2 in the lungs and bicarbonate (HCOs ) in the blood plasma (Fig. 1). 

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. 

A buffer system prevents marked changes in the pH of a solution when an acid or base is added. Three major buffer systems of the blood are the bicarbonate buffer, the phosphate buffer, and the plasma proteins. The most important of these is the bicarbonate buffer system, consisting of a mixture of bicarbonate ions (HCO3 ) and carbonic acid (H2CO3). 

The blood contains three major buffer systems the bicarbonate system, the phosphate system, and the plasma protein system. The most important is the bicarbonate system, which consists of a mixture of bicarbonate ions and carbonic acid. 

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