Final answer:
Chemoreceptors can accurately gauge arterial oxygen levels by detecting the partial pressure of dissolved oxygen, signaling the body to adjust respiratory rate and blood flow when these levels drop significantly, typically below 60 mm Hg.
Step-by-step explanation:
The reason that chemoreceptors can get accurate information about arterial O₂ levels is because they are finely tuned to detect changes in the partial pressure of dissolved oxygen in the blood. These peripheral chemoreceptors, located in the aortic arch and carotid arteries, are able to sense when blood oxygen levels fall to around 60 mm Hg or less, which signals a significant drop given that most oxygen in blood is tightly bound to hemoglobin. When dissolved oxygen levels decrease, hemoglobin releases oxygen, meaning these chemoreceptors effectively monitor the adequacy of oxygenation in the arterial blood before it affects the oxygen bound to hemoglobin.
As activity increases and metabolic byproducts such as carbon dioxide, hydrogen ions, and lactic acid build up in the blood, these chemoreceptors, which are innervated by the glossopharyngeal and vagus nerves, signal the cardiovascular and respiratory centers. The response is an increased respiratory activity to ensure proper gas exchange and maintain vascular homeostasis. Therefore, chemoreceptors provide critical feedback for regulating blood flow and breathing rate to meet the body's metabolic demands.