Hydrogen ion (pH): The peripheral and central chemoreceptors are also sensitive to the pH of the blood and CSF. If the hydrogen ion concentration increases (that is, if the fluid becomes more acidic), then the chemoreceptors tell the respiratory centers to speed up. Hydrogen ion concentration is heavily influenced by the carbon dioxide concentration and bicarbonate concentration in the blood and CSF.
Stretch: Stretch receptors in the lungs and chest wall monitor the amount of stretch in these organs. If the lungs become over – inflated (stretch too much), they signal the respiratory centers to exhale and inhibit inspiration. This mechanism prevents damage to the lungs that would be caused by over – inflation.
Signals from higher brain centers:Nerve cells in the hypothalamus and cortex also influence the activity of the respiratory centers. During pain or strong emotions, the hypothalamus will tell the respiratory centers to speed up. Nerve centers in the cortex can voluntarily tell the respiratory center to speed up, slow down or even stop (holding your breath). Their influence, however, can be overridden by chemical factors (oxygen, carbon dioxide, pH).
Chemical irritants: Nerve cells in the airways sense the presence of unwanted substances in the airways such as pollen, dust, noxious fumes, water or cigarette smoke. These cells then signal the respiratory centers to contract the respiratory muscles, causing you to sneeze or cough. Coughing and sneezing cause air to be rapidly and violently exhaled from the lungs and airways, removing the offending substance.
Of these factors, the strongest influence is the carbon dioxide concentration in your blood and CSF followed by the oxygen concentration.
