Oxygen-Haemoglobin Dissociation Curve
sigmoid shape of the oxy-Hb dissociation curve results from the allosteric interactions of the globin monomers that make up the haemoglobin tetramer as each one binds O2. Multiple factors can affect the affinity of Hb for oxygen, thus causing the curve to shift to the left (increased oxygen affinity) or to the right (decreased O2 affinity)