H.6.4+Explain+the+role+of+the+Bohr+shift+in+the+supply+of+oxygen+to+respiring+tissues.


 * The Bohr Effect/The Bohr Shift**

Bohr Effect:

Relationship between Bohr Effect and Chloride Shift: http://www.chemsoc.org/networks/learnnet/cfb/transport.htm



When carbon dioxide diffuses into the blood plasma and then into the red blood cells (erythrocytes) in the presence of the catalyst carbonic anhydrase most CO2 reacts with water in the erythrocytes and the following dynamic equilibrium is established:

H2O + CO2 ---> H2CO3

Carbonic acid, H2CO3, dissociates to form hydrogen ions and hydrogencarbonate ions. This is also a reversible reaction and undissociated carbonic acid, hydrogen ions and hydrogencarbonate ions exist in dynamic equilibrium with one another.

H2CO3 ---> H+ + HCO3-

The increase in H+ ions, in the blood decreases the blood's pH. As CO2 concentration increases, the O2 dissosciation curve shifts to the right (O2 dissosciation curve is essentially a pH curve). As seen on the graph, this decreases Hb's affinity for O2 (its ability to bind to O2 molecules). This makes the Hb O2 saturation lower; O2 is released from the haemoglobin to the surrounding cells.

The primary function of hemoglobin is to carry oxygen from the lungs to tissues. The Bohr Effect aids in this function by releasing oxygen to the tissues when the concentration of hydrogen ions becomes large.

Why is the Bohr Effect important? CO2 is produced in cellular respiration; the more energy the cells need, the more cellular respiration takes place, therefore the more CO2 is produced. Increased CO2 concentration shifts the curve to the right (decrease in pH). This causes a decrease in Hb saturation and therefore more oxygen to the cells. More oxygen to cells allows more cellular respiration to take place. The cycle continues like this, adjusting to blood pH levels. The Bohr Effect occurs during exercise for example.

At low pH the Bohr Effect allows the blood to unload oxygen for use by the muscles. Therefore, the Bohr Effect is necessary for the body to function.