What anatomical feature responds to both oxygen and carbon dioxide levels in the blood?

The carotid bodies are specialized chemoreceptors located at the bifurcation of the common carotid arteries. They play a crucial role in respiratory regulation by responding to changes in the levels of oxygen (O2) and carbon dioxide (CO2) in the bloodstream. Specifically, when oxygen levels are low or carbon dioxide levels are high, the carotid bodies send signals to the respiratory centers in the brain to adjust the breathing rate, thereby assisting in maintaining homeostasis.

In contrast, while the lungs are involved in gas exchange and can affect blood gas levels indirectly, they do not have intrinsic sensors for O2 and CO2 levels like the carotid bodies. The brainstem does participate in the control of ventilation but relies on input from chemoreceptors, including the carotid bodies, rather than having innate sensing capabilities. The heart primarily functions in pumping blood and although it can be influenced by changes in blood gases, it does not have the same direct sensing role as the carotid bodies. Thus, the carotid bodies are uniquely suited to respond to both oxygen and carbon dioxide levels, highlighting their essential function in regulating respiratory responses.