FILL IN EVALUATION FORM

EFFECT OF pH, CO₂ & TEMPERATURE

ON DISSOCIATION CURVES

• Changes in blood CO₂ and hydrogen ion concentration (pH) cause shifts in the oxygen dissociation curve. These shifts enhance oxygen release in tissues and enhance oxygen uptake in the lungs. This is known as the BOHR EFFECT

• In exercising tissues, PCO₂ is high and hydrogen ion concentration, [H⁺], is also high due to the formation of carbonic acid which dissociates to form bicarbonate ions and hydrogen ions (there is more information on this reaction in the carbon dioxide transport section). This increase in CO₂ and decrease in pH shifts the dissociation curve to the right for a given PO₂, releasing more oxygen to the tissues.

• In the lungs, PCO₂ is low and hydrogen ion (H⁺) concentration is also low. This decrease in CO₂ and increase in pH shifts the dissociation curve to the left for a given PO₂, enhancing oxygen uptake.

	The red line on the graph represents the dissociation curve at a normal pH (pH = 7.4). The green line represents the curve in the blood of exercising tissues, shifted to the right of the normal curve. The black line represents the curve in the blood at the lungs, shifted to the left of the normal curve.
Image reproduced from Mammalian Physiology lecture notes. Permission granted by Domnica Marghescu, Chief Technician, Physiology Department, McGill University

 

Higher PCO₂ = Higher [H+] = Lower pH = Shift to the RIGHT

Lower PCO₂ = Lower [H+] = Higher pH = Shift to the LEFT

• Increased temperature, such as in exercising tissues, shifts the curve to the right releasing oxygen.

• Decreased temperature shifts the curve to the left, enhancing oxygen uptake.

Back to oxygen dissociation curve