The Bohr shift describes the change in the affinity of haemoglobin for oxygen in response to changes in carbon dioxide concentration, pH, and temperature. This phenomenon is crucial for efficient oxygen delivery to tissues.
The Bohr Effect
The Bohr effect refers to the decrease in the oxygen-carrying capacity of haemoglobin when the partial pressure of carbon dioxide (pCO2) increases. This is a key aspect of the Bohr shift.
Mechanism of the Bohr Effect
The Bohr effect occurs due to the following mechanisms:
Increased H+ concentration: Carbon dioxide reacts with water to form carbonic acid ($CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$). This increases the concentration of hydrogen ions (H+), leading to a decrease in pH (increased acidity).
Reduced Haemoglobin Affinity for Oxygen: The increase in H+ concentration promotes the deoxygenation of haemoglobin. H+ ions bind to haemoglobin, altering its conformation and reducing its affinity for oxygen.
Increased Oxygen Release: As haemoglobin's affinity for oxygen decreases, oxygen is more readily released into the surrounding tissues.
The Bohr Shift
The Bohr shift is the graphical representation of the Bohr effect. It plots the relationship between the partial pressure of carbon dioxide (pCO2) and the oxygen saturation of haemoglobin.
Suggested diagram: A graph showing oxygen saturation of haemoglobin on the y-axis and pCO2 on the x-axis. The curve shows a decrease in oxygen saturation with increasing pCO2.
Importance of the Bohr Shift
The Bohr shift is of paramount importance for the efficient delivery of oxygen to metabolically active tissues. Here's why:
Enhanced Oxygen Delivery to Tissues: During exercise, tissues produce more carbon dioxide. The increased pCO2 in tissues triggers the Bohr shift, causing haemoglobin to release more oxygen. This ensures that tissues receive the oxygen they need for cellular respiration.
Regulation of Respiration: The Bohr effect plays a role in the respiratory drive. Increased carbon dioxide levels stimulate the respiratory centre in the brain, increasing ventilation to expel excess carbon dioxide.
Adaptation to Altitude: At high altitudes, the partial pressure of oxygen is lower. The Bohr effect helps to ensure that the oxygen that is available is efficiently released to the tissues.
Factor
Effect on Haemoglobin Oxygen Affinity
Increased pCO2
Decreases oxygen affinity (Bohr effect)
Decreased pH (Increased H+)
Decreases oxygen affinity (Bohr effect)
Increased Temperature
Decreases oxygen affinity (Bohr effect)
In summary, the Bohr shift is a vital physiological mechanism that ensures oxygen is delivered to where it is most needed. It is a direct consequence of the interplay between carbon dioxide, pH, and temperature on haemoglobin's oxygen-binding properties.