Editing Bohr effect (section)

== Physiological role ==
The Bohr effect increases the efficiency of oxygen transportation through the blood. After hemoglobin binds to oxygen in the [[lung]]s due to the high oxygen concentrations, the Bohr effect facilitates its release in the tissues, particularly those tissues in most need of oxygen. When a tissue's metabolic rate increases, so does its carbon dioxide waste production. When released into the bloodstream, carbon dioxide forms [[bicarbonate]] and protons through the following reaction:

:<chem>CO2 + H2O <=> H2CO3 <=> H+ + HCO3^-</chem>

Although this reaction usually proceeds very slowly, the enzyme [[carbonic anhydrase]] (which is present in [[red blood cells]]) drastically speeds up the conversion to bicarbonate and protons.<ref name = "Voet">{{cite book
 | last=Voet | first=Donald |author2=Judith G. Voet|author3=Charlotte W. Pratt
 | title=Fundamentals of Biochemistry: Life at the Molecular Level
 | publisher=John Wiley & Sons, Inc.
 | year=2013
 | edition=4th
 | pages=189
}}</ref> This causes the pH of the blood to decrease, which promotes the dissociation of oxygen from haemoglobin, and allows the surrounding tissues to obtain enough oxygen to meet their demands. In areas where oxygen concentration is high, such as the lungs, binding of oxygen causes haemoglobin to release protons, which recombine with bicarbonate to eliminate carbon dioxide during [[exhalation]]. These opposing [[protonation]] and deprotonation reactions occur in equilibrium resulting in little overall change in blood pH.

The Bohr effect enables the body to adapt to changing conditions and makes it possible to supply extra oxygen to tissues that need it the most. For example, when [[muscles]] are undergoing strenuous activity, they require large amounts of oxygen to conduct [[cellular respiration]], which generates CO<sub>2</sub> (and therefore HCO<sub>3</sub><sup>−</sup> and H<sup>+</sup>) as byproducts. These waste products lower the pH of the blood, which increases oxygen delivery to the active muscles. Carbon dioxide is not the only molecule that can trigger the Bohr effect. If muscle cells aren't receiving enough oxygen for cellular respiration, they resort to [[lactic acid fermentation]], which releases [[lactic acid]] as a byproduct. This increases the acidity of the blood far more than CO<sub>2</sub> alone, which reflects the cells' even greater need for oxygen. In fact, under anaerobic conditions, muscles generate lactic acid so quickly that pH of the blood passing through the [[muscles]] will drop to around 7.2, which causes haemoglobin to begin releasing roughly 10% more oxygen.<ref name="Voet"/>[[File:Bohr Effect Magnitude vs Body Size.png|thumb|The magnitude of the Bohr effect is given by <math display="inline">{\scriptstyle \Delta \log (P_{50}) \over \Delta \text{pH}}</math>, which is the slope on this graph. A steeper slope means a stronger Bohr effect.]]

=== Strength of the effect and body size ===
The magnitude of the Bohr effect is usually given by the slope of the  <math display="inline">\log (P_{50})</math> vs  <math display="inline">\text{pH}</math> curve where, [[P50 (pressure)|P<sub>50</sub>]] refers to the partial pressure of oxygen when 50% of haemoglobin's binding sites are occupied. The slope is denoted: <math display="inline">{\scriptstyle \Delta \log (P_{50}) \over \Delta \text{pH}}</math> where <math display="inline"> \Delta </math> denotes change. That is, <math display="inline">\Delta \log (P_{50})</math>  denotes the change in <math display="inline">\log (P_{50})</math> and <math display="inline">\Delta \text{pH}</math> the change in <math display="inline">\text{pH}</math>.
Bohr effect strength exhibits an inverse relationship with the size of an organism: the magnitude increases as size and weight decreases. For example, [[Mouse|mice]] possess a very strong Bohr effect, with a <math display="inline">{\scriptstyle \Delta \log (P_{50}) \over \Delta \text{pH}}</math> value of -0.96, which requires relatively minor changes in H<sup>+</sup> or CO<sub>2</sub> concentrations, while [[elephant]]s require much larger changes in concentration to achieve a much weaker effect <math display="inline">\left({\scriptstyle \Delta \log (P_{50}) \over \Delta \text{pH}} = -0.38\right)</math>.<ref name=":1" />