Buffer systems of the body

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.

However, one need not be unduly alarmed because in an active person, the buffer systems of the body are sufficiently efficient to maintain the pH in the 7.35-7.45 range. However, at the same time, the system should not be over worked by excessive intake of harmful foods and drinks. Long use of certain dmgs, such as steroids, can also severely compromise the functioning of our natural buffers. 

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. 

The body has three lines of defence buffering by the buffer systems of the body (blood, extracellular fluid, intracellular fluid and bone), respiratory compensa-... 

The first line of defence against a change in [H ] is provided by the buffer systems of the body. The buffers of the blood and extracellular fluid are immediately available whereas those of intracellular fluid take a matter of minutes to become effective. Because of its relatively low blood flow, bone, with an immense buffering power, requires hours or days to become available. 

The role of a buffer system in the body is important, because it tends to resist any pH changes as a result of metabolic processes. Large fluctuation in... 

A description of acid-base balance involves an accounting of the carbonic (H2C03, HCOh COa", and CO2) and noncar-bonic acids and conjugate bases in terms of input (intake plus metabolic production) and output (excretion plus metabolic conversion) over a given time interval. The acid-base status of the body fluids is typically assessed by measurements of total CO2 plasma pH and PCO2, because the bicarbonate/carbonic acid system is the most important buffering system of the plasma. Occasionally, measurement of total titratable acid or base, or other acid and base analytes (e.g., lactate and ammonia [NH3]) is necessary to determine the etiology of an acid-base disorder. 

Acid and base concentrations in living systems are carefully regulated to maintain conditions compatible with normal life. Biochemical reactions involving acids and bases occur in the body water, whereas buffer systems protect the body from significant variations in the concentrations of acids and bases. This chapter introduces basic concepts of the properties of water, acids, bases, and buffers, and Chapter 39 presents a detailed discussion of both normal and pathological aspects of acid-base metabolism. 

H. W. Haggard, The absorption, distribution, and elimination of ethyl ether III. The relation of the concentration of ether or any similar volatile substance in the central nervous system to the concentrations in arterial blood, and the buffer action of the body. J Biol Chem 59 771-781 (1924). 

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. 

Although the bicarbonate system is not the strongest buffer system in the body (the most powerful and plentiful one utilizes the proteins of plasma and cells), it is very important because the concentrations of both bicarbonate and carbonic acid are regulated by the kidneys and by the respiratory system. Without the respiratory and urinary processes, the capacity of buffers would eventually be exceeded. 

Loss of the weak acid and the addition of the neutral salt scarcely affect the hydrogen ion concentration in the body fluids. Thus, the carbonic acid-bicarbonate buffer system protects the body fluids from becoming either too acidic or too basic. 

In the term base bicarbonate, the word base refers to any base that might be combined with bicarbonate. In the main buffer system of the human body, this beise is sodium bicarbonate (NaH CO3). 

Prominent among these buffer systems of the animal body are the following —... 

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. 

One of the most important buffer systems in the human body is that which keeps the pH of blood around 7.4. If the pH of blood fall below 6.8 or above 7.8, critical problems and even death can occur. There are three primary buffer systems at work in controlling the pH of blood carbonate, phosphate, and proteins. The primary buffer system in the blood involves carbonic acid, H COj and its conjugate base bicarbonate, HCO3. Carbonic acid is a weak acid that dissociates according to the following reaction ... 

Daily body activities are quite sensitive to large pH changes, and must be kept within a small range of H30 and OH concentrations. Human blood, for example, has a pH of approximately 7.4 maintained by a buffer system. If our blood pH drops below 7.35, it can cause symptoms such as drowsiness, disorientation and numbness. If the pH level drops below 6.8, a person can die. To maintain pH stability, there is a carbonic acid - bicarbonate buffer system in the blood. 

Most of the acids we have in our bodies are produced as a result of the reactions going on inside the cells and only a small quantity is taken in as part of our food and drink. To make sure this externally added acidity does not grossly affect the mechanisms of the body cells and disturb the static state or homeostasis , the body has an in-built regulator or buffer system. 

As mentioned earlier, understanding the pH equation and the regulation and control of pH is fundamentally important when considering very many life and health processes. A simple indication of the importance of environmental pH is for growth of crops (soil pH) and acid rain (water pH), which can affect the ecosystem. Indeed, optimum conditions for purification of water and sewage treatment also are pH dependent. Physiologically, pH is critical to maintain normal body functions and key to biochemical reactions in the blood and other body fluids. Buffers and buffer systems are the primary means to regulate and maintain pH, and are discussed in more detail below (with examples in Appendix 3). 

The blood is not the only system in the body that has to have a fairly stable acid-base environment. Buffered aspirin is aspirin that has been altered so that it will not be too acidic and upsetting to the stomach. Many soaps and shampoos are specifically blended so that they do not differ significantly from the acid quality of the skin or hair. If there were a difference in acid quality, they could cause an acid-base reaction when applied. An acid-base reaction on the skin or in the eyes could cause damage to sensitive cells, which is why you are careful to use gloves and eye protection while doing these demonstrations. 

In Hamilton s early work, the sample was placed on the ion-exchange resin by removal of liquid at the top of the column and injection of the sample directly onto the top of the resin bed while the eluent flow was stopped. This is an adequate means of sample introduction, although an automated system can probably also be used. The chromatogram was developed with the stepwise elution by sodium citrate buffers of varying concentrations and pH from a typical sample of 0.5 ml of the body fluid (Fig. 15). 

Buffer solutions play an important role in many processes where the pH of a system needs to be maintained at an optimum value. For instance, several synthetic and processed foods contain buffers so that they may be digested without causing undue changes in the chemistry of the body. Buffer solutions are also important in agriculture and medicine for example, intravenous injections are carefully buffered so as not to alter the blood pH from its normal value of 7.4. 

The buffer systems of most physiological interest in connection with regulation of the pH of body fluids are those of plasma and eiythrocytes. Discussions of the most important physiological buffers foUow. 

Infection is the Achilles heel of the body and only with modern medicine has it been outrun by other diseases as the main cause of death. Therefore, there is tremendous evolutionary pressure on the immune system leading also to tremendous interindividual and species differences. The immune system also has enormous overcapacities, as it must be the last to fail. This will buffer chemical impacts on this organ system and indeed often only under additional stress of mass infection of an animal a functional deficit manifests. We have learned a lot from HIV pathophysiology about states of immunosuppression, in this case predominantly a T-cell impairment. Noteworthy, otherwise relatively rare skin cancers and reactivation of persisting infections were observed, which might suggest that... 

As was the case for the bicarbonate-carbonic acid system, the conjugate base form (HPO ) of the phosphate buffer is present in large (fourfold) excess compared to the acid form (H2PO4 ) and provides acid buffering capacity. Since the body metabolism produces more acid than... 

The body s buffering system can be divided into three components bicarbonate/carbonic acid, proteins, and phosphates. The bicarbonate buffer is the most important of the body s buffers, because (1) there is more bicarbonate present in the extracellular fluid (ECF) than any other buffer component (2) the supply of carbon dioxide is unlimited and (3) the acidity of ECF can be regulated by controlling either the bicarbonate concentration or the PCO2. 

The Chemistry in Action essay on p. 663 illustrates the importance of buffer systems in the human body. 

The level of total ketone bodies in Lofata Burne s blood greatly exceeds normal fasting levels and the mild ketosis produced during exercise. In a person on a normal mealtime schedule, total blood ketone bodies rarely exceed 0.2 mM. During prolonged fasting, they may rise to 4 to 5 mM. Levels above 7 mM are considered evidence of ketoacidosis, because the acid produced must reach this level to exceed the bicarbonate buffer system in the blood and compensatory respiration (Kussmaul s respiration) (see Chapter 4). 

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