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Respiratory Physiology

Respiratory Physiology. The primary function of the respiratory system is to exchange O2 and CO2 between blood and air. 1) Mostly covered in Lab; Control of Air Flow. Gas exchange (2,4) and Transport (3) Oxygen & Carbon Dioxide. Air must FLOW through airways to Alveoli

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Respiratory Physiology

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  1. Respiratory Physiology The primary function of the respiratory system is to exchange O2 and CO2 between blood and air 1) Mostly covered in Lab; Control of Air Flow Gas exchange (2,4) and Transport (3) Oxygen & Carbon Dioxide

  2. Air must FLOW through airways to Alveoli Alveoli are where gas exchange between air & blood occurs

  3. Factors affecting air flow Costs Energy > Diaphragm Contraction! Pulmonary Surfactant – decreases ST required to expand alveoli during inspiration 1) Pressure needed to expand sphere (alveoli) Pressure = Surface Tension Alveolar Radius Very Small>>>>>Huge Pressure Needed

  4. Medical Relevance of Surfactant Normal Infant Infant Respiratory Distress Syndrome (IRDS) Premature infants (< 32 weeks), leading cause of infant mortality in US

  5. Factors affecting Airflow 2) Airway Resistance = 1/ airway diameter Resistance increases as airway diameter decreases Smooth Muscle Smooth Muscle control: ANS, Hormones & Local Chemicals

  6. Smooth Muscle control: ANS, Hormones & Local Chemicals Bronchoconstriction (contraction of smooth muscle) ANS – Parasympathetic > acetylcholine > muscarinicreceptors (weak) Local – Histamines due to irritation or damage Bronchodilation (relaxation of smooth muscle) Hormonal -Epinephrine (adrenal) > β2 receptors (Epi-Pen for bee sting!) Local– high CO2 during expiration

  7. Alveolar-Blood Interface Membrane between Alveoli & Capillary is VERY VERY THIN …..increases diffusion rate

  8. Simple Diffusion & Partial Pressures Rate of Diffusion = Concentration Gradient Gas Concentrations are represented by Partial Pressures! High P Low P Diffusion is best over VERY VERY short distances…..that is why alveoli-blood interface is so thin

  9. Diffusion between Alveoli & Blood: OXYGEN Blood leaving Lungs has High PO2 Blood entering Lungs has Low PO2 Blood leaving Tissue has Low PO2 Blood entering Tissue has High PO2

  10. Diseases affecting O2 Diffusion

  11. Oxygen Transport in Blood • O2 diffuses into blood from Alveoli • 98% of diffused oxygen enter RBC • binds to Hemoglobin (Hb) • 3) 2% of oxygen remains in plasma • 4) At tissue, Hb + O2 dissociate • 5) O2 dissolves through plasma into ISF 1 3 2 4 5 Hemoglobin in RBC allows blood to carry 5000% more oxygen!

  12. Anemia: too few RBC 1) Iron Deficiency = no heme 2) B12 or Folate Deficiency = reduced DNA synthesis 3) Sickle Cell: hereditary

  13. Erythropoetin (EPO) EPO = Hormone controlling RBC synthesis Blood Doping = synthetic EPO supplement = more RBC = more O2 carrying capacity

  14. Diffusion between Alveoli & Blood: CO2 Blood entering Lungs has High PCO2 Blood leaving Lungs has Low PCO2 Blood entering Tissue has Low PCO2 Blood leaving Tissue has High PCO2

  15. Carbon Dioxide Transport in Blood 1) Dissolved CO2 ~ 7% • Diffusion from tissues to capillaries • Diffusion from venous blood to alveolar air

  16. Carbon Dioxide Transport in Blood 2) Hemoglobin transport ~ 23% 1 2 • CO2 diffuses into blood from tissues • CO2 binds to Hemoglobin (Hb) • 3) In lungs, Hb + CO2 dissociate • 4) CO2 dissolves into plasma and • diffuses to air in alveoli 4 3

  17. Carbon Dioxide Transport in Blood • CO2 dissolves into plasma • CO2 enters RBC and combines with water • Converted to HCO3- & Hb-H+ • by CARBONIC ANHYDRASE (CA) • 4) Cl- ion is exchanged for HCO3- • in CHLORIDE SHIFT • 5) HCO3- is carried in plasma to lungs • 6) Reverse of 3 & 4 • 7) CO2 dissolves in plasma and diffuses • to alveolar air 1 3) Bicarbonate Ion ~ 70% 4 2 3 5 7 6 HCO3- (Bicarbonate) is the most important pH buffer in blood Chloride Shift maintains RBC membrane electrical neutrality Hb-H+ helps maintain pH by using extra H+ ion from 2)

  18. Poor CO2 elimination – Respiratory dysfunction Why is removing CO2 important? Elevated CO2 = Hypercapnia Acidosis leads to denatured proteins & depressed brain function Elevated H+ leads to acidic blood Causes of Resp. Dys.: COPD, Emphysema, Musc Dystrophy, Asthma, Alcohol Use

  19. Control of Ventilation Chemoreceptor pathwaysALWAYS overrideVoluntary pathways You can’t hold you breath until you die! This is why you drown!!!!

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