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Control of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the neural mechanisms in controlling respiration. Describe the role of medullary centers in control of respiration Explain the function of pontine centers. Describe the 2 ty...

Control of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the neural mechanisms in controlling respiration. Describe the role of medullary centers in control of respiration Explain the function of pontine centers. Describe the 2 types of chemoreceptors. Explain mechanism of peripheral chemoreceptors stimulation by hypoxia. State the ventilatory (respiratory) responses to the changes in blood gases Control of breathing Neural control: Spontaneous respiration is produced by rhythmic discharge of motor neurons that innervate the respiratory muscles. This discharge is totally dependent on nerve impulses from the brain. Chemical control: The rhythmic discharges from the brain that produce spontaneous respiration are regulated by alterations in arterial PO2, PCO2, and H+ concentration Respiratory center Site: Medulla oblongata and Pons Medulla oblongata Pons Dorsal respiratory group(DRG) Pneumotaxic center Ventral respiratory group(VRG) Apneustic center Medullary center Are bilaterally located and bilaterally connected. They are Dorsal respiratory group (DRG) (Inspiratory center) Lies in the dorsal part of the medulla Function: 1. Generation of basic rhythm of respiration, rhythmic respiration is initiated by a small group of pacemaker cells in the pre-Bötzinger complex (pre-BÖTC). 2. Stimulation of DRE emit signals to → contraction of the diaphragm and external intercostal → inspiration. 3. Inhibition of DRE → relaxation of the diaphragm and external intercostal → Expiration. Medullary center Ventral respiratory group (VRG) (Expiratory center) Lie in the ventral part of the medulla. Are inactive during normal quiet breathing. Active during deep expiration Function: 1. Stimulation of VRG → contraction of abdominal and internal intercostal muscles → deep expiration Pontine center Apneustic center It is present in the lower part of the pons. Function: It stimulates DRG inspiratory neurons → prevents these neurons from being switched off and prolongs the duration of inspiration. Pneumotaxic center It is present in the upper pons. Function: play a role in switching between inspiration and expiration It inhibits the DRG inspiratory neurons → (shortens) the duration of inspiration and increases the rate of breathing. Hering –Breuer's reflex Afferent from vagus nerve has the same effect of Pneumotaxic center. Stimulus: when the lungs are overstretched → stimulation of stretch receptors in the wall of the bronchi and bronchioles → inhibition of inspiratory center → decrease the duration of inspiration and increase the rate. Neural control of respiration The function of respiratory center is regulated by afferent impulses from. 1. Higher centers: brain (voluntary control) and hypothalamus (Pain, emotion) 2. Lung: example, Hering-Breuer reflex 3. The air passages: sneezing, Cough and swallowing 4. Circulatory system: Increase venous return →stimulate respiratory system to increase ventilation of this venous return. 5. Skeletal muscles and joints: exercise increase respiration 6. Visceral reflex: swallowing and vomiting inhibit respiration Chemical Control of breathing Respiration Stimulated by Inhibited by 1. Increased PCO2 in arterial blood 1. Decreased PCO2 in arterial blood 2. Increased H+ in arterial blood. 2. Decreased H+ in arterial blood. 3. Decreased O2 in arterial blood 3. Increased O2 in arterial blood These chemical factors exert their effect through central and peripheral chemoreceptors Chemical Control of breathing Central chemoreceptors Site: chemosensitive area , which is bilaterally located in the medulla Stimulus: This area is highly sensitive to changes in either blood PCO2 or H+ concentration. H+ concentration is the primary stimulus for central chemoreceptors. H+ cannot cross the blood brain barrier, so the source of H+ in the brain is from CO2. CO2 cross the blood brain barrier. CO2 + H2O → H2CO3 by carbonic anhydrase Enzyme, then H2CO3 → H+ and HCO3Stimulates Central chemoreceptors Does metabolic acidosis stimulate central chemoreceptors???? Why??? Chemical Control of breathing Peripheral chemoreceptors Site: Carotid bodies: bifurcation of the common carotid → Glossopharyngeal nerve → DRG Aortic bodies: along the aortic arch → vagus nerve → DRG Stimulus: 1. Decreases arterial PO2 (Mainly). 2. Increased arterial PCO2. 3. Increased arterial H+ concentration. Chemical Control of breathing Decreases arterial PO2 (Mainly for peripheral chemoreceptor). Decrease arterial PO2 due to decrease alveolar PO2 level which occurs in 1. Closed overcrowded area. 2. High altitude. Maximum effect of Decrease PO2 is 5 to 6 times increase in ventilation Increases arterial PCO2 (weaker stimulation of peripheral chemoreceptor) Increase arterial PCO2 (hypercapnia) occurs in Muscle exercise Effect : Stimulation of respiration → lead to decrease PCO2 back to normal. Maximum effect of increase PCO2 is 11 times increase in ventilation. Chemical Control of breathing Increase arterial PCO2 stimulates both central and peripheral chemoreceptors. But central chemoreceptors produce more powerful response (7 times) than peripheral chemoreceptors. Chemical Control of breathing Increases arterial H+ concentration (weaker stimulation of peripheral chemoreceptors) Increases arterial H+ concentration occurs in Metabolic acidosis → stimulates peripheral chemoreceptors → stimulation of respiration. Maximum effect of increase H+ (decrease PH to 7) is 4 times increase in ventilation Summary Describe the neural mechanisms in controlling respiration. Describe the role of medullary centers in control of respiration Explain the function of pontine centers. Describe the 2 types of chemoreceptors. Explain mechanism of peripheral chemoreceptors stimulation by hypoxia. State the ventilatory (respiratory) responses to the changes in blood gases Learning Resources  Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2021. Chapter 42 , 531 – 540. https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000424  Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF MEDICINE Thank you