Hemoglobin buffer system

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 phosphate buffer system (pH 6.5 - 7.0) Is useful for detecting small quantities of the hemoglobins H and Bart s these variants will both move toward the anode while Hb-A remains at the origin. Figure 3 gives some examples of separations that can be obtained. 

Figure 8.5 Effect of pH on protein mobility. Hemoglobin A (pi 7.1) and Hemoglobin C (pi 7.4) were electrophoresed in eight of the McLellan native, continuous buffer systems (Table 8.1). The diagram is drawn to scale. Migration is from top to bottom as shown by the vertical arrows. Bands marked A or C indicate the positions of the two hemoglobin variants in each gel representation. The polarities of the voltages applied to the electrophoresis cell are indicated by + and - signs above and below the vertical arrows. Run times are shown below the arrows. Note the polarity change between the gel at pH 7.4 and the one at pH 8.2. This reflects the pis of the two proteins (and was accomplished by reversing the leads of the electrophoresis cell at the power supply).

Blood travels through the human body in more than 96,000 km of blood vessels and it is full of marker molecules [34], The physiological pH is usually 7.4 with a complex buffer system (bicarbonate-carbonic acid, hemoglobinate-hemoglobin, phosphate buffer) [35],... 

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.

Excess carbonic acid present in blood is to a great extent buffered by the hemoglobin and protein buffer systems (see Figure 46-9). The buffering of CO2 causes a slight rise in cHCOT Thus in the immediate posthypercapnic state,... 

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 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 oxygen-carrying capacity of the hemoglobin in your blood and the activity of the enzymes in your cells are very sensitive to the pH of your body fluids. Our bodies use a combination of compounds known as a buffer system to keep the pH within a narrow range. 

The internal and external buffering systems were included in the computations as follows. The important intracellular buffer is hemoglobin, and its buffer capacity under the conditions of these experiments was assumed to be 2.54 mM acid/mM Hb/pH 28, 29). Extracellularly, hemoglobin concentrations were very low, and other buffers (water, lactate, phosphate, etc.) became important. Therefore, an empirical buffering curve for the extracellular fluid was determined by plotting concentration of acid added vs. the plateau pH values. Then, the buffering power of the extracellular fluid at any given extracellular pH was assumed to equal the slope of the curve at that pH. 

Fig. 4.9. Buffering systems of the body. COj produced from cellular metabolism is converted to bicarbonate and H in the red blood cells. Within the red blood cell, the is buffered by hemoglobin (Hb) and phosphate (HP04 ). The bicarbonate is transported into the blood to buffer Regenerated by the production of other metabolic acids, such as the ketone body acetoacetic acid. Other proteins (Pr) also serve as intracellular buffers.

CO2 and water and more hydrogen ions to combine with bicarbonate. Hemoglobin loses some it of its hydrogen ions, a feature that allows it to bind oxygen more readily (see Chapter 7). Thus, the bicarbonate buffer system is intimately linked to the delivery of oxygen to tissues. 

In blood, the main buffer system is bicarbonate at a concentration of [HCOj"] = 0.02-0.03 M (20-30 mEq/ I). Hemoglobin provides a further 10 mEq/l buffer capacity, and phosphate makes a small contribution of 1.5 mEq/l. The 5 liters of blood in an average adult human are thus able to absorb about 0.15 mole before the pH becomes dangerously low. The major buffers of the body are, however, present in other tissues. The total musculature of the body, for example, can neutralize about 5 times as much acid as the blood, and the blood HCO37CO2 system represents only about a tenth of the total buffer capacity of the body. Since all the buffer systems of the body are able to interact and buffer each other, all changes in the acid/ base balance of the body are reflected in the blood. This mutual buffering by the shift of H from one body system to another is known as the isohydric principle. 

In order to achieve high concentrations of HCOj" from dissolved CO2, the resulting protons must be removed, i.e. accommodated by a buffer system. The principal buffers serving this function are plasma proteins (accounting for about 10% of the protons), erythrocyte phosphate (about 20%) and erythrocyte hemoglobin (60-70%). For the role of hemoglobin, see Bohr effect. Hemoglobin. 

In laboratory reactions, in industrial processes, and in the bodies of plants and animals, it is often necessary to keep the pH nearly constant despite the addition of acids or bases. The oxygen-carrying capacity of the hemoglobin in your blood and the activity of the enzymes in your cells are very sensitive to the pH of your body fluids. A change in blood pH of 0.5 units (a change in [H3O+] by a factor of about 3) can be fatal. Our bodies use a combination of compounds known as a buffer system to keep the pH within a narrow range. 

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