When you hold your breath, which of the following blood gas changes first leads to the urge to breathe? a. rising O2 b. falling O2 c. rising CO2 c, falling CO2

Key Concepts

Role of Carbon Dioxide (CO2) in Breathing

Carbon dioxide is a key regulator of respiration. When you hold your breath, CO2 levels in the blood begin to rise due to continued metabolic activity, leading to increased acidity in the blood. This rise in CO2 is detected by chemoreceptors, which signal the brain to initiate the urge to breathe.

Oxygen (O2) Levels and Breathing Regulation

Oxygen levels in the blood are also monitored by chemoreceptors, but they play a secondary role in the urge to breathe compared to CO2 levels. While a significant drop in O2 can trigger breathing, it typically occurs after CO2 levels have already risen, making the response to CO2 more immediate and critical in regulating breath.

Chemoreceptors and Respiratory Control

Chemoreceptors are specialized cells that detect changes in the chemical composition of the blood, particularly levels of CO2, O2, and pH. Central chemoreceptors located in the brainstem are primarily sensitive to CO2 levels, while peripheral chemoreceptors in the carotid and aortic bodies respond to both O2 and CO2. Their activation is crucial for maintaining homeostasis and regulating the respiratory rate.