Breathing Regulation Notes

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Breathing control

Pulmonary chemoreceptors and mechanoreceptors

NOTES NOTES BREATHING REGULATION BREATHING CONTROL osms.it/breathing-control WHAT IS BREATHING CONTROL? ▪ Breathing (ventilation): movement of gasses in, out of lungs ▪ Regulation maintains arterial partial pressures of O2, CO2 (PaO2, PaCO2) ▪ Components: brainstem respiratory centers; peripheral, central chemoreceptors; mechanoreceptors in lungs, muscles of respiration, joints BRAINSTEM RESPIRATORY CENTERS Dorsal respiratory group (DRG) ▪ Inspiratory center, located in dorsal medulla ▪ Sets basic rhythm of breathing ▪ Receives sensory input via cranial nerves (CN) IX, X from peripheral chemoreceptors, mechanoreceptors in lungs → sends motor output via phrenic nerve to stimulate contraction of diaphragm ▫ DRG neurons generate repeating bursts of action potentials → period of quiescence ▫ Bursts occur → action potential frequency “ramps up” → ↑ lung volume Ventral respiratory group (VRG) ▪ Expiratory center, located in ventral medulla ▪ Inactive during basic, quiet breathing ▪ Provides high respiratory drive when ventilation needs to increase (e.g. exercise) Pneumotaxic center ▪ Located in upper pons ▪ Limits inspiration by inhibiting DRG ▪ Limits tidal volume, increases respiratory rate ▪ Receives input from cerebral cortex Apneustic center ▪ Located in lower pons ▪ Prolongs DRG inspiratory signal, diaphragm contraction → inspiratory gasps (apneusis) ▪ Associated with damage to pons/upper medulla VOLUNTARY CONTROL Cerebral cortex ▪ Sends commands to voluntarily override autonomic control of ventilation ▪ Hyperventilation ▫ Voluntarily breathing at rate > that needed by metabolism ▫ Self-limiting: hyperventilation → ↓ PaCO2 (strongly inhibits autonomic respiratory centers, ventilation) ▪ Hypoventilation ▫ Voluntarily breathing at rate insufficient for metabolism ▫ Self-limiting: hypoventilation → ↓ PaO2, ↑ PaCO2 HYPOTHALAMIC CONTROL ▪ Strong emotions, pain: act via hypothalamus, limbic system → signal respiratory centers → modify respiratory rate, depth ▪ Rise in body temperature → ↑ respiratory rate ▪ Drop in body temperature → ↓ respiratory rate OSMOSIS.ORG 601
PULMONARY CHEMORECEPTORS & MECHANORECEPTORS osms.it/pulmonary-central-peripheral-chemoreceptors CENTRAL CHEMORECEPTORS ▪ Located in ventral surface of medulla ▪ Sensitive to changes in H+ indirectly by sensing acute changes in PaCO2 (unable to cross blood-brain barrier) ▫ ↑ PaCO2 → conversion to carbonic acid (H2CO3) by enzyme carbonic anhydrase → dissociation into H+, HCO3- → ↓ CSF pH (↑ CSF [H+]) → stimulates central chemoreceptors → stimulates DRG → ↑ ventilation → ↓ PaCO2 (40mmHg) ▪ Crucial minute-to-minute control ▫ Match ventilation with metabolism by monitoring PaCO2 Irritant receptors ▪ Respond to noxious gasses; particulates via CN X → coughing, bronchoconstriction Juxtacapillary (J) receptors ▪ Located in alveoli, near capillaries ▪ Respond to capillary engorgement → ↑ respiratory rate PERIPHERAL CHEMORECEPTORS ▪ Located in carotid bodies at bifurcation (near aortic arch) ▪ Responds directly to changes in PaO2, PaCO2 ▫ Strongly stimulated in linear fashion when PaO2 < 60mmHg ▫ Weakly stimulated by ↑ PaCO2 ▫ Carotid bodies only: stimulated by ↑ arterial [H+] ▪ Afferents send information to DRG via CN IX, X → directs ventilatory response to hypoxemia, acidemia, alkalemia MECHANORECEPTORS Lung stretch receptors ▪ Located in airway smooth muscle ▪ Respond to lung inflation → termination of inspiration (Hering–Breuer inspiratoryinhibitory reflex) Joint and muscle receptors ▪ Respond to bodily movement → ↑ respiratory rate 602 OSMOSIS.ORG Figure 69.1 The brainstem is the respiratory center of the body. Many receptors throughout the body send signals to the brainstem so that it can regulate the breathing rate accordingly.

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This Osmosis High-Yield Note provides an overview of Breathing Regulation essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Breathing Regulation by visiting the associated Learn Page.