Final answer:
The breathing rate in mammals is most directly controlled by the level of CO2 in the blood. Chemoreceptors in the brain and cardiovascular system detect changes in CO2 levels and signal the respiratory centers to adjust breathing accordingly, maintaining homeostasis.
Step-by-step explanation:
Breathing Rate Control in Mammals
The breathing rate in mammals is most directly controlled by the level of CO2 in the blood. This is because the primary trigger for the respiratory centers in the brainstem, which includes the medulla oblongata, are changes in blood CO2 concentration. When CO2 levels rise, chemoreceptors located in the brain and in the blood vessels (like the aortic arch and carotid arteries) signal for an increase in the rate and depth of breathing to expel the excess CO2,
These mechanisms work continuously and automatically, reacting to even slight fluctuations in CO2 concentration to maintain blood pH and gas homeostasis. Consequently, when CO2 levels in the blood decrease, the brain signals the diaphragm and other breathing muscles to slow down the breathing rate, conserving CO2 in the blood.
It is the interplay of various chemoreceptors and the respiratory centers that ensures mammals maintain a balanced internal environment, allowing our bodies to function optimally in varying conditions.