Plan
► Control of respiration:
• general concepts of regulatory mechanisms of respiration;
• concept of reflex mechanisms of respiration, characteristics of the main reflex regulatory mechanisms of respiration (receptors, reflexogenic zones, afferent nerves, nervous center, efferent nerves, effector organs, feedback channels); origin of respiration rhythm and its modification under varying environmental conditions; humoral regulatory mechanisms of respiration.
► Functional system for optimization of gas composition of the internal environment of an organism.
Control of Respiration
General Concepts of Regulatory Mechanisms of Respiration
Regulation is a complex of central and peripheral mechanisms that work in cooperation to provide useful adaptive results vital for an organism.
According to the modern classification, these results may be metabolic, homeostatic, behavioral and social.
Results achieved by respiratory mechanisms are the optimal level of gases and optimal acid-alkaline balance in the internal environment of the body, in other words, the optimal levels of PCO2, pH and PO2. In adults, the main controllers of breathing are PCO2-sensitive mechanisms. In newborns, breathing is controlled by PO2-sensitive mechanisms.
Physiological functions are regulated by neuroreflex and humoral mechanisms.
In breathing both inborn (unconditioned) and acquired (conditioned) reflexes participate. Inborn reflexes are subdivided into proper and conjuga-
ted ones. In a proper respiratory reflex, excitation from chemoreceptors controlling pCO2, pO2 and pH goes directly to the nerve center, without involving any intermediate elements. In conjugated reflexes, excitation may arise from any receptors capable of initiating a reflex (temperature receptors, nocice-ptors, olfactory, taste receptors, etc.), and at first goes to the nerve centers of the reticular formation and only from there to the respective nerve centers. Thus, reticular formation is an intermediate element of a conjugated reflex. For example, stimulation of thermal receptors may cause a change in rhythm and depth of breathing through initial change in the activity of nerve centers of reticular formation in the brainstem.