What is the function of haemoglobin

It can easily join with oxygen in areas of the body where there is a high oxygen concentration, like in the lung capillaries. When haemoglobin chemically combines with oxygen, oxyhaemoglobin is produced. When haemoglobin reaches areas of the body where the oxygen concentration is low, eg respiring cells, oxyhaemoglobin will quickly release the oxygen, which then diffuses into cells