Regarding the physiology of the respiratory system, it is...

Inhalation: intrapulmonary pressure is greater than atmospheric pressure, allowing air to enter from the atmosphere into the lungs; when pressures equalize, air entry ceases.

If the pH is below normal (acidosis), the respiratory center is stimulated, increasing the frequency and amplitude of respiratory movements.

Exhalation: intrapulmonary pressure becomes lower than atmospheric pressure due to muscular relaxation, causing air to exit.

Tidal Volume (TV): the volume of air inspired and expired during one minute."