Blood pH The normal pH of blood is around 7.35, which is the optimal pH for the majority of enzymes in our body. If the blood pH changes significantly, serious medical problems can occur due to denaturation of proteins and enzymes. There are basically three main mechanisms that regulate the body’s blood pH level

1) Acid-Base Buffer System The blood has a carbonic acid (H2CO3) - bicarbonate ion (HCO3 - ) buffer system to prevent serious changes in its pH. If there is an increase in acidity (H+): H+ + HCO3-  H2CO3 If there is an increase in alkalinity (OH-): OH- + H2CO3  HCO3- + H2O These reactions prevent any significant change in blood pH over the short term.

2) Lungs/Respiratory Centre The blood pH is also monitored by the medulla oblongata. If it is too acidic, the medulla oblongata increases the breathing rate which generates CO2. H+ + HCO3-  H2CO3  H2O + CO2 Getting rid of CO2 at the lungs pulls the equilibrium to the right and reduces the amount of H+.

The Kidneys They are the most powerful of the mechanisms controlling blood pH as they can reabsorb or expel acidic or basic substances very quickly from the body and thereby change blood pH substantially. If the blood is too acidic, the kidneys expel and secrete H+ and reabsorb HCO3-. If the blood is too basic, the kidneys will not excrete H+ and will not reabsorb any HCO3-. The kidney is also able to use the buffering power of ammonia (NH3) to aid in its maintenance of blood pH.