Final answer:
The primary stimulus for respiration in a healthy, awake cat is the blood concentration of carbon dioxide. This concentration influences the respiratory centers in the brain, which control the rate and depth of respiration to maintain homeostasis.
Step-by-step explanation:
In the healthy, awake cat, the primary stimulus in blood for respiration is carbon dioxide (B). The major factor that stimulates the respiration centers in the medulla oblongata and pons is the concentration of carbon dioxide in the blood. As carbon dioxide levels increase, it diffuses across the blood-brain barrier, leading to an increase in hydrogen ions and a decrease in pH. This stimulates central chemoreceptors, which signal the respiratory centers to increase the rate and depth of respiration. The increase in respiration assists in expelling more carbon dioxide from the blood, regulating the blood pH levels. Peripheral chemoreceptors located in the carotid arteries and aortic arch also sense changes in blood pH and carbon dioxide levels, further influencing respiratory rates.
Both respiratory rate and depth are controlled by the respiratory centers of the brain, which are stimulated by chemical and pH changes in the blood. These changes are essential in maintaining homeostasis within the body, ensuring that both oxygen and carbon dioxide levels, as well as pH, are kept within normal limits.