Question

In chronic breathing conditions, the central chemoreceptors are continually exposed to high PCO2 levels and they stop responding to changes in PCO2 as the primary stimulus to breathe. What stimulates breathing in these individuals?

Answer 1

For individuals with chronic breathing conditions that result in desensitized central chemoreceptors, peripheral chemoreceptors that sense significant decreases in blood oxygen levels are the primary stimulators of breathing. When oxygen levels drop severely, these receptors trigger an increase in respiratory rate.

Step-by-step explanation:

In individuals with chronic breathing conditions where central chemoreceptors are desensitized to high PCO2 levels, breathing is primarily stimulated by peripheral chemoreceptors. These are located in the carotid arteries and aortic arch and are sensitive to large changes in blood oxygen levels. When blood oxygen levels fall significantly for instance to 60 mm Hg or less, these peripheral chemoreceptors signal an increase in the respiratory rate.

This is because the receptors can sense dissolved oxygen in the blood not oxygen bound to hemoglobin. Hemoglobin will release oxygen when dissolved levels drop, indicating severe hypoxemia that then prompts increased respiratory effort to enhance oxygen intake and carbon dioxide expulsion. The relationship between the cardiovascular and respiratory systems is crucial, as they work together to ensure proper oxygen delivery and carbon dioxide removal in response to metabolic demands. Moreover the respiratory centers in the brain, such as the medulla oblongata are also indirectly influenced by changes in the pH of cerebrospinal fluid (CSF) due to metabolic activities, such as lactic acid accumulation following strenuous exercise, which can also affect the respiratory rate.