respiratory gas transport n.
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RESPIRATORY GAS TRANSPORT
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  1. RESPIRATORY GAS TRANSPORT

  2. OXYGEN TRANSPORT • 98.5% oxygen in arterial blood is bound to hemoglobin and 1.5% is dissolved in plasma • Each heme group of 4 globin chains in a hemoglobin molecule may bind O2 • After binding with O2, hemoglobin changes shape to allow further uptake (positive feedback) • An oxyhemoglobin dissociation curve shows relationship between hemoglobin saturation and oxygen partial pressure - PO2.

  3. Oxyhemoglobin Dissociation Curve

  4. CARBON DIOXIDE TRANSPORT • 90% as carbonic acid in plasma CO2 + H2O  H2CO3  HCO3-+ H+ • 5% as carbaminohemoglobin (HbCO2)- binds to amino groups of Hb (and plasma proteins) • 5% as dissolved gas in plasma

  5. SYSTEMIC GAS EXCHANGE • CO2 loading • carbonic anhydrase in RBC catalyzes • CO2 + H2O  H2CO3  HCO3-+ H+ • chloride shift • keeps reaction proceeding, exchanges HCO3-for Cl- (H+ binds to hemoglobin) • O2 unloading • H+ binding to HbO2 causes  affinity for O2 • Hb arrives 97% saturated, but leaves 75% saturated(venous reserve) • Utilization coefficient (amount of oxygen Hb has released) is 22%

  6. ALVEOLAR GAS EXCHANGE • Reactions are the reverse of systemic gas exchange • O2 loading & CO2 unloading • as Hb loads O2 its affinity for H+ decreases, H+ dissociates from Hb and binds with HCO3- • CO2 + H2O  H2CO3  HCO3-+ H+ • reverse chloride shift • HCO3-diffuses back into RBC in exchange for Cl-and free CO2 diffuses into alveoli to be exhaled

  7. Alveolar Gas Exchange

  8. Systemic Gas Exchange

  9. FACTORS FAVORING OXYGEN UNLOADING • Metabolic needs of tissues affect O2 unloading (HbO2 releases O2) • Low ambient PO2: tissue has  PO2 • Increased temperature of tissue • Bohr effect: tissue has  CO2, which raises H+ and lowers pH • bisphosphoglycerate (BPG):BPG produced by RBCs as a metabolic intermediate binds to Hb and causes HbO2 to release O2 •  body temp. (fever), TH, GH, testosterone, and epinephrine raise BPG and cause O2 unloading

  10. Oxygen Dissociation & pH Active tissue - more O2 released Bohr effect: release of O2 in response to low pH

  11. FACTORS FAVORING CARBON DIOXIDE LOADING • Metabolic needs of tissues affect CO2 loading • Haldane effect: low level of oxyhemoglobin(HbO2) enables blood to transport more CO2 • HbO2 does not bind CO2 as well as deoxyhemoglobin (HHb) does. • HHb binds more H+ than HbO2- The CO2 + H2O  HCO3-+ H+ reaction therefore shifts to the right

  12. CHEMORECEPTORS • Monitor pH, PCO2, PO2 of body fluids • Peripheral chemoreceptors • aortic bodies - signal medulla by vagus nerves • carotid bodies - signal medulla by glossopharyngeal nerves • Central chemoreceptors on surface of medulla • primarily monitor pH of cerebrospinal fluid

  13. Peripheral Chemoreceptor Pathways

  14. DIRECT CARBONDIOXIDE EFFECT ON CHEMORECEPTORS •  CO2 may directly stimulate peripheral chemoreceptors and trigger  ventilation more quickly than central chemoreceptors

  15. DIRECT EFFECT OF OXYGEN ON CHEMORECEPTORS • Usually, oxygen has little effect on chemoreceptors. • Chronic hypoxemia, PO < 60 mmHg, as is associated with emphysema & pneumonia may cause increased ventilation .