Haemoglobin oxygen release

Figure 5.17 Superoxide generation during oxygen release from haemoglobin...

B26. Benesch, R., and Benesch, R. E., Intracellular organic phosphates as regulators of oxygen release by haemoglobin. Nature London) 221, 618-622 (1969). 

The in situ generation of 2,3 BPG is accelerated by low atmospheric Po2, for example at high altitude. Lower Po2 at altitude could compromise tissue oxygenation so to avoid cellular hypoxia, 02 is released from haemoglobin. 

Another, and more acute, trigger to the release of oxygen from haemoglobin is the pH of the blood surrounding the red cell. Protons arising from metabolic activity of tissues cause a right-shift in the position of the ODC and oxygen is released when the pH falls. This phenomenon is called the Bohr effect. 

Fully oxygenated haemoglobin releases one atom of O2 and the haem group-iron remains in the reduced state. 

Physiologically, oxygen transport to metabolising tissues is provided by haemoglobin contained within erythrocytes. This pathway starts in the bone marrow with immunohaematopoietic stem cells that differentiate to progenitors which proliferate to yield the recognisable normoblasts. The latter mature to reticulocytes, which are then released into the circulation. Overall regulation is primarily mediated by the renal hormone called erythropoietin. 

One of the most important functions of blood is the binding of oxygen by haemoglobin and its transport to the tissues. Administration of blood and blood products, however, carries with it a number of risks (Table 20.3) and are not always the initial choice to replace blood or plasma loss. Blood and blood products are also expensive, have a limited availability, and a very limited shelf life. A number of alternative oxygen-carrying fluids have been developed, and some are close to release for clinical use. 

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