26.21 : 呼吸中枢に影響を与える化学的要因

CO₂, O₂, and H⁺ ion levels affect the rate of respiration.

These changes are detected by the central chemoreceptors in the brain stem, and the peripheral chemoreceptors in the aortic arch and the bifurcations of the common carotid arteries.

In hypercapnia, an increased level of arterial P_CO2 drives the diffusion of CO₂ from the blood to the cells, forming carbonic acid.

This carbonic acid then dissociates, liberating H⁺ ions, which are detected by the central chemoreceptors in the brain, triggering an intensified breathing pace.

Conversely, peripheral chemoreceptors can detect increased P_CO2 directly and also respond to increased H⁺ ion levels.

Normally, blood oxygen levels influence breathing indirectly by altering chemoreceptor sensitivity to changes in CO₂.

The peripheral chemoreceptors respond to oxygen levels only when arterial P_O2 falls below 60 mmHg.

At this point, the breathing rate increases, creating a feedback loop: increased breathing decreases P_CO2 and increases the blood pH, both of which inhibit respiration.

As a result, the breathing rate is slowly restored to normal.