2.4.1 Chemical and mechanical control mechanisms

The chemical factors that govern respiration rate and depth are O₂, CO₂, and H⁺ (pH) (Fig. 17). CO₂ / pH is the strongest stimulus for respiration. In other words, it is not the amount of O₂ in our blood that is most essential for the respiration regulation. The body is more concerned with the amount of CO₂, rather than the amount of O₂ in the blood. This can be explained by that fact that the blood is normally 100% saturation with O₂. Thus, there is a large reserve of O₂, so whether you breathe more or less O₂ levels do not change very much particularly in normal, resting conditions. However, the body has a big challenge if CO₂ builds up. We recall that CO₂ and pH are closely related, and a high level of CO₂ will result in a lower pH in the blood. This must be carefully controlled for so as not to disrupt the biochemical processes in the body by disrupting the acid-base balance. For these reasons, CO₂ / pH are the strongest stimuli for controlling respiration.

Receptors in the aortic arch and the arteries leading blood to the brain detect changes in CO₂ in the blood.

In addition to the chemicals, there are stretch receptors in the lung tissue, muscles and joints that stimulates respiration (Fig. 17). For example, during a jog, respiration will increase even before the need for additional O₂ has been detected because the stretch receptors in the muscles and joints are activated immediately during increased activity and consequently stimulate respiration so that the body is prepared for this activity.’

Fig. 17