Blood pH during exercise is regulated mainly by chemical buffers and increased ventilation, with the kidneys contributing more slowly. Together, these mechanisms use negative feedback to keep arterial blood pH close to its normal range of approximately to .
During intense exercise, increased ATP turnover leads to greater accumulation of hydrogen ions, , which would lower pH. Working muscles also produce more carbon dioxide, which enters the blood and reacts as follows:
An increase in shifts blood toward acidosis. Several coordinated mechanisms oppose this change.
| Regulatory mechanism | Role during exercise |
|---|---|
| Bicarbonate buffer system | Bicarbonate ions, , bind excess . The resulting carbonic acid is converted into water and carbon dioxide. |
| Protein and phosphate buffers | Haemoglobin and other proteins temporarily bind , limiting rapid changes in pH. |
Central and peripheral chemoreceptors provide the detection component of this homeostatic loop. Peripheral chemoreceptors in the carotid and aortic bodies respond to falling pH and rising carbon dioxide, while central chemoreceptors respond indirectly to carbon dioxide changes. Ventilation then acts as the effector response. As acidity decreases, receptor stimulation falls, preventing an excessive corrective response.
A common misconception is that lactate directly causes the fall in pH. Lactate formation is associated with high-intensity exercise, but the principal source of accumulating is rapid ATP breakdown; lactate production can temporarily consume .
In an IB SEHS response on A.1.2 Maintaining homeostasis, identify the disturbance, receptor or detection process, control response, and return toward the set range. Distinguish immediate buffering and respiratory responses from slower renal regulation, and explicitly link increased ventilation to carbon dioxide removal.
