Tissue Factors
The release of oxygen from haemoglobin to the tissues is facilitated by the steep lower part of the haemoglobin dissociation curve. This enables large amounts of oxygen to be released from the blood for only a small drop in the partial pressure of oxygen in the capillaries.
A variety of local factors can also affect the ability (or affinity) of the haemoglobin molecules to carry oxygen whilst they circulate in the capillaries perfusing the tissues.
The most important of these factors is the acidosis in the tissues as a result of their metabolic activity. This local fall in the pH (rise in H+) has the effect of ‘shifting’ the haemoglobin dissociation curve to the right of its position in the graph i.e. for a given partial pressure of arterial oxygen the saturation is less. This means that more oxygen is released in close proximity to the tissues, which require it.
The graph illustrates the effect of ph changes on the O2Hb dissociation curve.
The same effect is seen with increases in:
Temperature
Partial pressure of CO2
