Question

select all that apply
indicate two changes that will trigger increased alveolar ventilation.

increased blood ph
decreased blood ph
decreased blood levels of co₂
increased blood levels of co₂

Explanation:

• Decreased blood pH: A decrease in blood pH (more acidic) often indicates an increase in hydrogen ions. This can be due to increased carbon dioxide levels (as \(CO_2 + H_2O

ightleftharpoons H_2CO_3
ightleftharpoons H^++HCO_3^-\)). The body's respiratory center (in the medulla oblongata) is sensitive to changes in pH. A lower pH (more acidic) stimulates the respiratory center to increase alveolar ventilation. This helps to blow off \(CO_2\) (since \(CO_2\) is a major contributor to the acid - base balance in the blood as shown in the carbonic acid - bicarbonate buffer system).

• Increased blood levels of \(CO_2\): \(CO_2\) is a major regulator of ventilation. When \(CO_2\) levels in the blood rise, it can combine with water in the cerebrospinal fluid (CSF) to form carbonic acid (\(CO_2 + H_2O

ightleftharpoons H_2CO_3\)). The dissociation of carbonic acid (\(H_2CO_3
ightleftharpoons H^++HCO_3^-\)) increases the \(H^+\) concentration in the CSF. Chemoreceptors (central chemoreceptors in the medulla and peripheral chemoreceptors in the carotid and aortic bodies) detect this change. The respiratory center is then stimulated to increase the rate and depth of breathing (alveolar ventilation) to expel the excess \(CO_2\).

• Increased blood pH: An increased blood pH (more alkaline) would inhibit the respiratory center. This is because the body wants to retain \(CO_2\) (since \(CO_2\) contributes to acidity when it forms carbonic acid) to bring the pH back to normal. So, it would not trigger increased alveolar ventilation.
• Decreased blood levels of \(CO_2\): A decrease in \(CO_2\) levels would make the blood (and potentially the CSF) less acidic (or more alkaline if the decrease is significant). This would lead to a decrease in the stimulation of the respiratory center, and thus a decrease in alveolar ventilation rather than an increase.

Answer:

B. decreased blood pH, D. increased blood levels of \(CO_2\)