Which change in blood chemistry causes an increase in respiration rate?

• A. An increase in blood pH
• B. A decrease in blood \(\mathrm{CO_2}\) concentration
• C. A decrease in blood \(\mathrm{O_2}\) concentration
• D. An increase in blood \(\mathrm{CO_2}\) concentration

Answer: (D)

Verified step by step guidance

1. Understand the relationship between blood chemistry and respiration rate: Respiration rate is regulated by the body's need to maintain homeostasis, particularly in response to changes in blood levels of oxygen (\(\mathrm{O_2}\)), carbon dioxide (\(\mathrm{CO_2}\)), and pH.
2. Recognize the role of carbon dioxide (\(\mathrm{CO_2}\)): When \(\mathrm{CO_2}\) levels in the blood increase, it reacts with water (\(\mathrm{H_2O}\)) to form carbonic acid (\(\mathrm{H_2CO_3}\)), which dissociates into hydrogen ions (\(\mathrm{H^+}\)) and bicarbonate ions (\(\mathrm{HCO_3^-}\)). This process lowers blood pH, making it more acidic.
3. Understand the body's response to increased \(\mathrm{CO_2}\): Chemoreceptors in the brainstem (specifically in the medulla oblongata) and in peripheral areas like the carotid and aortic bodies detect the increase in \(\mathrm{CO_2}\) and the associated drop in pH. These chemoreceptors signal the respiratory center to increase the rate and depth of breathing.
4. Compare the effects of other changes: An increase in blood pH (alkalosis) or a decrease in \(\mathrm{CO_2}\) concentration would typically decrease respiration rate, as the body perceives less need to expel \(\mathrm{CO_2}\). A decrease in \(\mathrm{O_2}\) concentration can also increase respiration rate, but this effect is less sensitive compared to \(\mathrm{CO_2}\) levels.
5. Conclude that the correct answer is an increase in blood \(\mathrm{CO_2}\) concentration, as it directly triggers an increase in respiration rate to expel excess \(\mathrm{CO_2}\) and restore pH balance.