When a human increases physical activity,
the amount of fuel burned in its cells also
increases, which in turn increases the
concentration of dissolved CO2 in the blood.
The CO2 reacts with water in the blood to
make a weak acid, which lowers the pH of
the blood. Sensory cells in the medulla of
the brain register this drop in pH and send
signals to the diaphragm and heart to
ncrease respiration. This will clear the CO2
from the bloodstream. positive feedback loop or negative feedback loop