Human blood is slightly alkaline with pH 7.4 and it does not change by the addition of a small amount of acid and base because:

Explanation

Human blood is slightly alkaline with a pH of 7.4. The pH of blood is maintained within a narrow range, and it does not change significantly by the addition of a small amount of acid or base because of the presence of serum proteins in blood. Serum, the plasma component of blood which lacks coagulation factors, is similar to the interstitial fluid in which the correct composition of key ions acting as electrolytes is essential for normal functioning of muscles and nerves.Serum proteins act as buffers that help to maintain the pH of blood within a narrow range.They can accept or donate hydrogen ions (H+) to resist changes in pH when an acid or base is added to the blood. In serum, the key compounds H2CO3 + NaHCO3 are present that act as buffer system.Buffer system H2CO3+NaHCO3 resists change in pH of blood therefore pH value of blood remains unchanged by a small addition of an acid or a base.