Final answer:
Respiration is mainly regulated by CO2 levels through central and peripheral chemoreceptors, though low oxygen levels can also stimulate respiration, especially in conditions like COPD where CO2 sensing mechanisms may be impaired.
Step-by-step explanation:
The regulation of respiration in the body primarily involves carbon dioxide (CO2) levels as the main stimulus for breathing, rather than oxygen levels. Sensing the concentration of CO2 is crucial as it directly ties to the acidity (pH level) in the blood. This is because as CO2 levels rise in the bloodstream, it forms carbonic acid, which dissociates into hydrogen ions, lowering the pH. The brain detects changes in pH and CO2 through central chemoreceptors within the brain itself and peripheral chemoreceptors in the aortic arch and carotid arteries.
When the peripheral chemoreceptors sense a significant drop in dissolved oxygen levels (below 60 mm Hg), they trigger an increase in respiratory activity. However, this large drop in oxygen is needed because the chemoreceptors do not sense oxygen bound to hemoglobin. It is important to note that in conditions like COPD, there may be a reliance on low oxygen levels to drive respiration due to the destruction of CO2 sensing mechanisms, a condition known as 'hypoxic drive.'