National League for Nursing (NLN PAX) Practice Exam

Increased CO2 concentration in the blood during physical activity primarily stimulates the respiratory rate. As muscles work harder, they produce more carbon dioxide as a byproduct of increased metabolism. This rise in CO2 levels leads to a decrease in blood pH (making the blood more acidic). The body detects the increased levels of CO2 through chemoreceptors, which are sensitive to changes in the composition of the blood. To compensate for the higher carbon dioxide levels and to regulate acid-base balance, the respiratory center in the brain increases the rate and depth of breathing. This response enhances the expulsion of CO2 and allows for greater intake of oxygen, supporting the elevated demands of physical activity.

The other options do not align with the physiological responses during exercise. For instance, decreased oxygen supply to muscles would not be an effect of increased CO2; rather, the body works to increase oxygen delivery during physical exertion. Similarly, the heart rate typically increases to enhance blood flow and oxygen delivery to tissues, rather than being reduced. Additionally, increased CO2 concentration generally leads to a lower blood pH, not an increase, due to the formation of carbonic acid from CO2 in the blood. Thus, the increase in the respiratory rate directly reflects the body’s