Respiring tissues in the body produce carbon dioxide which diffuses into the blood. Most of it then enters red blood cells where an enzyme named carbonic anhydrase catalyses a reaction to produce carbonic acid. This dissociates rapidly into hydrogen ions and hydrocarbonate ions. The Hydrogen ions combine very readily with haemoglobin to form a compound known as haemoglobinic. There are two effects of this reaction.
1. Hydrogen ions are removed from the blood making it less acidic.( haemoglobin acts as a PH buffer)
2. As haemoglobin picks up the hydrogen ions it releases oxygen.
Oxyhaemoglobin dissociation curve
The sigmoid curve means that as the deoxygenated blood approaches lungs a small increase in partial pressure of oxygen causes a large increase in the percentage of saturation and as oxygenated blood approaches the tissues a small decrease in partial pressure of oxygen will lead to a large decrease in percentage of saturation of oxygen.
Fetal haemoglobin needs to have a higher affinity…