Respiratory homeostasis

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  • Respiratory homeostasis
    • Steps in external respiration
      • 2. Gas exchange between lungs and blood via diffusion
      • 1. Pulmonary ventilation
      • 3. Transport of oxygen and carbon dioxide in blood to tissues
      • 4. Gas exchange between blood and tissues via diffusion
    • Aortic bodies
      • peripheral chemoreceptors responsible for sensing changes in blood gases are called 'glomus cells'.
      • Aortic bodies are several small clusters of chemoreceptors, baroreceptors, and supporting cells located along the aortic arch.
    • What can effect the response of ventilation?
      • H+
        • Peripheral  receptors are highly sensitive to fluctuations in [H+].              ? [H+] stimulate ventilation     ? [H+] repress ventilation- these changes are far less important than CO2's central effects
        • H+ cannot influence central chemoreceptors. Changes in arterial CO2 will produce changes in arterial H+
      • PCO2
        • only weakly stimulates peripheral, more responsive
        • potently stimulates (major ventilation control), chemoreceptors found next to medullary respiratory centres
      • PO2
        • peripheral only stimulated in life threatening conditions (40% reduction, < 60mmHg)
        • directly depresses both central chemoreceptors and respiratory centres themselves
    • respiratory centres
      • primary centre is medullary respiratory centre
        • collection of aggregations of neuronal cell bodies within medulla and in the pons
        • different centres
          • Apneustic  centre (pons)
            • Prevents inspiratory neurones from being 'switched off'This provides a boost to inspiration. Pneumotaxic centre dominates over apneustic
          • pneumotaxic centre (pons)
            • Sends signals to the DRG to 'switch off' inspiratory neuronesThis limits the duration of inspiration, prevents lungs from over expanding
          • Dorsal respiratory group (medulla) DRG
            • Consists mostly of inspiratory neurones
            • Firing causes inspiratory muscles to contract, causing inspiration
            • Subsequent cessation of firing causes inspiratory muscles to relax leading to passive expiration
            • Neurones fire again and inspiration restarts (cycle)
          • Ventral respiratory group (medulla) VRG
            • Consists of both inspiratory and expiratory neurones
            • Especially involved in active expiration- VRG is innervated by DRG and can response in times of need to increase inspiration - e.g. exercise
            • Both types remain inactive during normal 'quiet' breathing.  Only used in times of increased demand
      • 3 distinct components
        • factors that generate inspiration-expiration rhythm
        • factors that regulate the magnitude of ventilation
        • factors that modify respiration to serve other purposes
    • HCRG
      • consists of motor neurones, increased CO2 in blood causes pH to decrease - causes acidosis - spinal cord can take over in extreme cases, can mediate small amount of respiration

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