Respiratory System Physiology PDF

Kinesiology 132 Systems Physiology II Respiratory System – RS2 Today’s topics: Ventilation Breathing regulation – eupnea to more forceful, influences Ventilation – regulation – areas Breathing – how it works – still somewhat disputed. Medullary Respiratory Center (MRC): Pre-Bötzinger Com...

Kinesiology 132 Systems Physiology II Respiratory System – RS2 Today’s topics: Ventilation Breathing regulation – eupnea to more forceful, influences Ventilation – regulation – areas Breathing – how it works – still somewhat disputed. Medullary Respiratory Center (MRC): Pre-Bötzinger Complex – possible “pacemaker” sending signal to DRG to initiate breathing. Dorsal Respiratory Group (DRG) – composed of inspiratory neurons. Ventral Respiratory Group (VRG) – composed of inspiratory and expiratory neurons.  Ventilation – eupnea regulation DRG (inspiratory neurons) active inactive 2 seconds 3 seconds diaphragm/external intercostal diaphragm/external intercostal contract recoil eupnea inspiration eupnea expiration DRG inspiratory neurons: Cycling between active and inactive. Eupnea: ~5 seconds for inspiration and expiration – breathing frequency = 12 bpm; typical eupnea breathing frequency 6 – 16 bpm. Morphine, barbiturates, fentanyl, and heroin can suppress DRG inspiratory neurons (overdose deaths with these substances often involve breathing stopping).  Ventilation – more forceful regulation DRG (inspiratory neurons) active inactive diaphragm/external intercostal diaphragm/external intercostal contract stronger recoil more more forceful more forceful inspiration expiration DRG inspiratory neurons still cycling (active/inactive) like at eupnea but a stronger active contraction and more inactive recoil.  Ventilation – even more forceful regulation DRG (inspiratory neurons) active inactive diaphragm/external intercostal diaphragm/external intercostal contract stronger recoil more even more forceful even more forceful inspiration expiration accessory muscles accessory muscles inspiration contract expiration contract VRG inspiratory neurons expiratory neurons At a certain point stronger diaphragm/external intercostal contraction/recoil not enough on its own. DRG recruits VRG to provide active/inactive cycling of inspiratory/expiratory neurons to accessory muscles of inspiration and expiration. Ventilation – regulation – influences Pontine Respiratory Group In pons. Exactly how it works? Likely sends signal to DRG influencing switch between active and inactive to modify breathing pattern. Good examples of influence seen during swimming and speaking. Ventilation – regulation – influences Mechanoreceptors – detect mechanical changes and provide input to DRG. 2 examples: Proprioceptors In joints and muscles. Respond to changes in body movement (eupnea to exercise). Function: help match ventilation to movement needs; likely involved in when to recruit VRG. Slow adapting mechanoreceptors In smooth muscle surrounding airways. Contribute to Hering-Breuer reflex – end inspiration by switching DRG from active to inactive if lung volume gets too large. Protective function: prevents overexpansion damaging lung tissues. Ventilation – regulation – influences Chemoreceptors – detect chemical changes and provide input to DRG. Peripheral chemoreceptors: In carotid sinus and aortic arch (same locations as arterial baroreceptors). Respond to changes in arterial blood. Central chemoreceptors: In medulla oblongata. Respond to changes in brain extracellular fluid. Carotid sinus Aortic arch  Ventilation – regulation – influences ↑ Altitude ↑ Activity ↑ nonCO2 acids (like lactic ↓ Arterial O2 ↑ Arterial CO2 acid) ↑ Brain extracellular CO2 ↑ Arterial [H+] ↑ Brain extracellular [H+] ↑ firing peripheral ↑ DRG inspiratory ↑ firing central chemoreceptors neurons cycling chemoreceptors active/inactive ↑ Ventilation [ ] = concentration Ventilation – regulation – influences From higher brain centers Considered anything above brainstem (medulla oblongata, pons, midbrain). Mainly cerebrum and/or cerebellum. Example Apnea – stopping breathing. Limited ability to over ride involuntary breathing. Critical levels: Decrease arterial oxygen enough – unconsciousness – involuntary breathing should resume. Increase arterial CO2 enough – involuntary breathing starts. Apnea Manipulation – interesting – but not testable Hyperventilating before apnea – alter arterial blood levels (especially CO2): Starting apnea from a lower arterial CO2 – can hold breath longer before reach critical level and involuntary breathing starts – good or bad? Example Free diving – apnea while underwater Shallow water blackout: Oxygen reaches critical low level and go unconscious / involuntary breathing starts. And/or CO2 reaches critical high level / involuntary breathing starts. If still underwater when involuntary breathing starts – drowning risk. Apnea: trainable Average person breath hold: ~30 sec – 2 min. Records: Breathing air before starting apnea: ~11 min breath hold. Breathing pure oxygen before starting apnea: ~24 min breath hold.