National League for Nursing (NLN PAX) Practice Exam

During exercise, one of the primary physiological responses is an increase in carbon dioxide (CO2) concentration in the blood. This occurs because the working muscles produce more CO2 as a byproduct of increased metabolism and energy expenditure. The body's respiratory centers in the brain detect this elevated level of CO2, which is a major stimulant for the respiratory drive.

As a response to higher CO2 levels, the body increases the respiratory rate to enhance the expulsion of CO2 and improve oxygen uptake. Effectively, the increase in respiratory rate allows for better ventilation, helping to maintain acid-base balance and ensuring that the body has sufficient oxygen to meet the metabolic demands of exertion.

Other options do not accurately explain the physiological mechanism at play during exercise. For example, an increase in O2 concentration would not lead to a respiratory increase; the body seeks to manage CO2 levels primarily. Additionally, a decrease in heart rate or physical activity would not drive an increase in respiratory rate, as both would lead to less demand for oxygen and less CO2 production. The body’s physiological responses during exercise are finely tuned to promote optimal gas exchange and homeostasis, centering around the management of CO2 levels.