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Chapter 22 Respiratory System Lecture 8 Part 3: Control of Respiration

Marieb’s Human Anatomy and Physiology Marieb w Hoehn. Chapter 22 Respiratory System Lecture 8 Part 3: Control of Respiration. Control of Respiration. Homeostatic mechanisms intervene so that cellular gas exchange needs are met Control occurs at two levels 1. Local regulation

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Chapter 22 Respiratory System Lecture 8 Part 3: Control of Respiration

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  1. Marieb’s Human Anatomy and Physiology Marieb w Hoehn Chapter 22 Respiratory System Lecture 8 Part 3: Control of Respiration

  2. Control of Respiration • Homeostatic mechanisms intervene so that cellular gas exchange needs are met • Control occurs at two levels 1. Localregulation • Lung perfusion (blood flow; ~5.5 L/min); Q • Alveolar ventilation (~4.2 L/min); V • Ventilation/perfusion (V/Q) coupling/matching 2. Respiratorycenter of the brain

  3. Local Control of Respiration • Local Control regulates… • Efficiency of O2 pickup in the lungs • Lung perfusion (blood flow, Q) • Alveolar arterioles constrict when local PO2 is low • Tends to shunt blood to lobules with high PO2 • Alveolar ventilation (air flow, V) • High PCO2 (hypercapnia) causes bronchodilation • Low PCO2 (hypocapnia) causes bronchoconstriction • Directs airflow to lobules with higher PCO2 • Rate of O2 delivery in each tissue • Changes in partial pressures • Local vasodilation in peripheral tissues

  4. Factors Affecting Resistance to Airflow • Diameter of bronchioles • Bronchodilation (epinephrine, sympathetic stimulation) • Bronchoconstriction (parasympathetic stimulation, histamine, cold air, chemical irritants) • Surface tension of alveoli and distal bronchioles.

  5. Neural Control of Respiration Figure from: Hole’s Human A&P, 12th edition, 2010 Neural control of respiration has an autonomic as well as a voluntary component

  6. Regulation of Breathing Ventral Respiratory group (VRG) appears to be the rhythm-generating and integrative center Dorsal Respiratory group (DRG) integrates input from peripheral stretch receptors and chemoreceptors and sends info to VRG **Together, the VRG and DRG in the respiratory rhythmicity center of the medulla regulate rate and depth of breathing.

  7. Factors Affecting Breathing Central chemoreceptors Respond to PCO2 and pH of the CSF Effect is actually due to [H+] as follows: CO2 + H2O ↔ H2CO3 H2CO3↔ H+ + HCO3- Bicarbonate Carbonic acid Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

  8. Factors Affecting Breathing Figure from: Hole’s Human A&P, 12th edition, 2010 Both central and peripheral chemoreceptors are subject to adaptation Decreased blood PO2 or pH (or increased CO2) stimulates peripheral chemoreceptors in the carotid and aortic bodies Stimulation leads to anincrease in the rate and depth of respiration CO2 is the most powerful respiratory stimulant

  9. Factors Affecting Breathing • motor impulses travel from the respiratory center to the diaphragm and external intercostal muscles • contraction of these muscles causes lungs to expand • expansion stimulates stretch receptors in the lungs • inhibitory impulses from receptors to respiratory center prevent overinflation of lungs (Hering-Breuer reflex) Figure from: Hole’s Human A&P, 12th edition, 2010 CO2 is the most powerful respiratory stimulant

  10. Control of Respiration - Summary • Control of respiration is accomplished by: 1) Local regulation 2) Nervous system regulation • Local regulation •  alveolar ventilation (O2),  Blood flow to alveoli •  alveolar ventilation (O2),  Blood flow to alveoli •  alveolar CO2, bronchodilation •  alveolar CO2, bronchoconstriction

  11. Control of Respiration - Summary • Nervous System Control • TheVRG in and DRG in the respiratory rhythmicity center of the medulla regulate rate/depth of breathing • Changes in breathing • CO2 is most powerful respiratory stimulant • Recall: H2O + CO2↔ H2CO3 ↔ H+ + HCO3- • Peripheral chemoreceptors (aortic/carotid bodies) •  PCO2,  pH ,  PO2 stimulate breathing • Central chemoreceptors (medulla) •  PCO2,  pH stimulate breathing

  12. Breathing Reflexes • Protective Reflexes • Sneezing - Triggered by an irritation of the nasal cavity • Coughing – Triggered by an irritation of the larynx, trachea, or bronchi • Both sneezing and coughing involve • A period of apnea • Forceful expulsion of air from lungs opening the glottis (up to 100 mph or more!!) • Laryngeal spasms – chemical irritants, foreign objects, or fluids into the area around glottis • Temporarily closes the airway • Some stimuli, e.g., toxic gas, can close the glottis so powerfully that it doesn’t open again!

  13. Control of Respiration • Control of respiration is accomplished by: 1) Local regulation 2) Nervous system regulation • Local regulation •  alveolar ventilation (O2),  Blood flow to alveoli •  alveolar ventilation (O2),  Blood flow to alveoli •  alveolar CO2, bronchodilation •  alveolar CO2, bronchoconstriction

  14. Control of Respiration • Nervous System Control • TheVRG in and DRG in the respiratory rhythmicity center of the medulla regulate rate/depth of breathing • Changes in breathing • CO2 is most powerful respiratory stimulant • Recall: H2O + CO2↔ H2CO3 ↔ H+ + HCO3- • Peripheral chemoreceptors (aortic/carotid bodies) •  PCO2,  pH ,  PO2 stimulate breathing • Central chemoreceptors (medulla) •  PCO2,  pH stimulate breathing

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