Final answer:
When the parasympathetic nervous system is dominant, it affects the respiratory system by regulating CO₂ levels. It stimulates cardioaccelerator and vasomotor centers, increasing cardiac output and constricting peripheral vessels when CO₂ levels are high. Conversely, it stimulates cardioinhibitor centers and suppresses cardioaccelerator and vasomotor centers when CO₂ levels are low.
Step-by-step explanation:
When the parasympathetic nervous system (PSNS) is dominant, it affects the respiratory system. The chemoreceptors in the body respond to increasing carbon dioxide (CO₂) levels and falling pH by stimulating the cardioaccelerator and vasomotor centers, leading to an increase in cardiac output and constriction of peripheral vessels. This helps to maintain adequate supplies of oxygen to the cells and remove waste products such as CO₂. On the other hand, when CO₂ levels decrease and pH increases, the cardioinhibitor centers are stimulated, while the cardioaccelerator and vasomotor centers are suppressed. This leads to a decrease in cardiac output and peripheral vasodilation.