Buffering of blood

Again, buffers are essential in keeping pH within defined limits so that biochemical reactions can occur with maximum efficiency (i.e. maintaining so-called homeostasis). If, for example, the pH gets too low, the acidic environment can damage (or denature) and thus disable enzymes. An important example is the buffering of blood by the carbonic acid-bicarbonate buffer system illustrated below ... 

Other nonbicarbonate buffers of blood are present at <10 mmol/L concentration. 

The process of respiration plays an important role in the buffering of blood. In particular, an increase in H concentration can be dealt with by raising the rate of respiration. Initially, the added hydrogen ion binds to bicarbonate ion, forming carbonic acid. 

Figure 1.18. Buffering of blood. Roleo/HCO" ondHbO /HUbO buffers.

From the foregoing discussion we can conclude that the main buffering qrstems of blood are the HCO 3 /H CO, HbO /HHbO. and Hb"/HHb. In addition, blood contains numerous proteins and many substances possessing phosphate groups. Thus, two additional buffering systems which operate in blood are HPO /H PO and proteinate /protein systems. These systems, however, contribute less to the buffering of blood than the main sterns discussed above. 

An important example of a buffered system is that found in blood, which must be maintained at a pH of 7.4 in humans. We consider the buffering of blood in the Focus On feature for this chapter on the MasteringChemistry website. But buffers have other important applications, too. 

This difference in behavior for acetic acid in pure water versus water buffered at pH = 7 0 has some important practical consequences Biochemists usually do not talk about acetic acid (or lactic acid or salicylic acid etc) They talk about acetate (and lac tate and salicylate) Why Its because biochemists are concerned with carboxylic acids as they exist in di lute aqueous solution at what is called biological pH Biological fluids are naturally buffered The pH of blood for example is maintained at 7 2 and at this pH carboxylic acids are almost entirely converted to their carboxylate anions... 

Biomedical Applications. TRIS AMINO is used for a number of purposes in its pure form, it is an acidimetric standard the USP grade can be utilized intraveneously for therapeutic control of blood acidosis TRIS AMINO also is useful in genetic engineering as a buffering agent for enzyme systems, industrial protein purification, and electrophoresis. AMP has found use as a reagent in enzyme-linked immunoassays. The primary appHcation is for alkaline phosphatase assays. 

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

Blood is buffered mainly by the HC03 -H2C03 buffer system. The normal pH of blood is 7.40. 

Human blood contains a variety of acids and bases that maintain the pH very close to 7.4 at all times. Close control of blood pH Is critical because death results if the pH of human blood drops below 7.0 orrises above 7.8. This narrow pH range corresponds to only a fivefold change in the concentration of hydronium ions. Chemical equilibria work in the blood to hold the pH within this narrow window. Close control of pH is achieved by a buffer solution, so called because it protects, or buffers, the solution against pH variations. 

Electropherogram of blood serum on cellulose acetate. (Buffer 0.50 M barbitone, pH = 8.6)... 

Interestingly, a closely related prodrug of doxorubicin that has the same spacer (i.e., 6.33) was found to be a good substrate for plasmin while being stable in buffer and blood serum [55], A marked selectivity was seen against a plasmin-generating MCF-7 breast cancer cell line. 

Reaction of l with raw human hlood samples Since blood samples contained anticoagulant, buffer and blood (itself a composite of various chemicals) hence C.V. studies of l" were also carried out on blood sample in the absence and the presence of buffer and anticoagulant. PBS (buffer) -1- anticoagulant showed the presence of an electroactive moiety which could undergo electro-oxidation in the range 0.000-1.000 V However, addition of 1 ml of this buffer -1- anticoagulant solution to 9 ml of 0.5 mM r solution moved the anodic peak cathodically from 456 to 170 mV. 

Fig. 27.3 Cyclic voltammogram of effect of blood (containing anticoagulant + buffer) on 5 mM K1 (0.1m NaCl, aqueous sysfem)...

In humans, the pH of blood is held at a remarkably constant value of 7.4 0.05. hi severe diabetes, the pH can drop to pH 7.0 or below, leading to death from acidotic coma. Death may also occur at pH 7.7 or above, because the blood is unable to release CO2 into the lungs. The pH of blood is normally controlled by a buffer system, within rather narrow limits to maintain life and within even narrower limits to maintain health. 

Due to their high concentration, plasma proteins—and hemoglobin in the erythrocytes in particular—provide about one-quarter of the blood s buffering capacity. The buffering effect of proteins involves contributions from all of the ionizable side chains. At the pH value of blood, the acidic amino acids (Asp, Glu) and histidine are particularly effective. 

Dialysis units provided highly efficient means for increasing selectivity in a dynamic system by placement in front of a lithium-selective electrode constructed by incorporating 14-crown-4 ether 3-dodecyl-3 -methyl-1,5,8,12-tetraoxacyclotetradecane into a PVC membrane that was in turn positioned in a microconduit circuit by deposition on platinum, silver or copper wires. The circuit was used to analyse undiluted blood serum samples by flow injection analysis with the aid of an on-line coupled dialysis membrane. For this purpose, a volume of 200 pL of sample was injected into a de-ionized water carrier (donor) stream and a 7 mM tetraborate buffer of pH 9.2 was... 

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