Blood CO2

• The regulation of CO2 levels in the blood is detected by chemoreceptors
• Once the chemoreceptors detect a change in CO2 levels, they transmit this information to the respiratory centres in the brainstem (medulla oblongata and pons)
• Upon receiving signals from the chemoreceptors, the respiratory centres in the brainstem initiate responses to regulate CO2 levels
• Increased CO2 levels (Hypercapnia) 

  • The respiratory centres stimulate the phrenic nerve, which initiates the diaphragm, and other motor neurons  that control the intercostal muscles
  • This leads to an increase in the rate and depth of breathing (hyperventilation), which helps expel more CO2 from the lungs, thereby lowering CO2 levels in the blood
• Decreased CO2 levels (hypocapnia) 

  • The respiratory centres reduce the stimulation of the phrenic nerve and other respiratory muscles 
  • This results in a decrease in the rate and depth of breathing (hypoventilation), which allows CO2 to accumulate in the blood, thereby raising CO2 levels back to normal