5. Gas transport - Richard

• PaO2 (partial pressure) drives HbO2 (saturation)
• • When O2 is not bound to Hb (deoxyhemoglobin) - the globin unit for tightly bound in tense (T) configuration
  • Decrease Affinity
• • When O2 is first bound, the bond holding the globin unit are released --> relaxed (R) configuration, which exposes more O2 binding sites
  • Increase Affinity
• • Loading phase - there is increased binding of O2 to Hb
  • When PO2 is high (as in pulmonary capillaries) oxygen is loaded onto hemoglobin to form oxyhemoglobin
• • Unloading phase - there is decreased binding of O2 to Hb
  • When PO2 is low (as in tissue capillaries) large quantities of O2 are released or unloaded from hemoglobin in tissue capillaries
• • HIF-2 activation
  • Due to hypoxia caused by mutation or drugs
  • Will induces renal >>> hepatic erythropoietin (EPO) synthesis
  • Leading to increase in serum EPO levels
  • Stimulation of erythropoiesis
• what can be beneficial to O2 unloading at tissue levels?

  reduction of Hb-O2 affinity
• What can cause increase in 2,3-BPG?

  • hyperventilation
  • increase CO2 removal
  • increase in blood pH
  • increase glycolysis
• An increase in pH stimulates glycolysis - contributing to increase concentration of 2,3 DPG
• A decrease in pH of the blood decreases affinity of Hb for O2.

  
• • Increase acidity = decrease pH - oxygen-hemoglobin dissociation curve shifts to right
  • decreasing affinity of hemoglobin for blood

  
• What can cause blood to become more acidic?

  exercise
• The Bohr effect describes

  • hemoglobin lower affinity for oxygen secondary to increase partial pressure of carbon dioxide or decrease blood pH

  
• • CO binds Hb to form carboxyhemoglobin (HbCO)
  • HgB + CO --> HbCO
• oxygen-hemoglobin dissociation curve

  • Shift to right - lower affinity
  • Shift to left - higher affinity
• • Myoglobin
  • Expressed in skeletal muscle
  • Binds 1 mol of O2 - instead of 4
  • Lack of cooperative binding (curve is not sigmoid)
  • Has higher affinity for O2 (curve is shifted to left)
  • O2 is released from myoglobin only at low PO2
• 15 grams of hemoglobin in each 100 milliliters of blood

  • Each gram of hemoglobin can bind a maximum of 1.34 milliliter of O2
  • What is the oxygen carrying capacity of hemoglobin?   
  • 15 x 1.34 equal about 20 milliliter of blood
• • Carbon monoxide is dangerous
  • CO is undetectable being
  • Odorless
  • Colorless
  • Nonirritating gas
• CO is undetectable

  • PaO2 is normal - no feedback signaling to indicate that oxygen content is low
  • no cyanosis - CO blood is bright red
  • ABG analyzer - SaO2 based on PaO2
  • Pulse oximetry
  • SpO2 is dependent on optical absorption but since O2 and CO have the same color - SpO2 = normal
• • In CO poisoning, O2 carrying capacity of Hb is reduced, therefore total blood O2 content are reduced
  • **PaO2 is unaffected
• How do you treat CO poisoning

  • Give pure O2
  • O2 at higher alveolar pressure can displace CO
  • Administer CO2 to stimulate respiratory center to increase alveolar ventilation
  • Reducing alveolar CO
• increase CO2 = decrease blood pH
• Chloride shift

  • HCO3- ions diffuse out of RBC facilitated by Cl-HCO3 exchanger
  • Chloride ions move inward --> electrical neutrality maintained
  • Venous RBC - has higher Cl- compared to arterial RBC
  • Venous RBC have a slightly larger volume than arterial RBC
  • Venous plasma has lower Cl- than arterial plasma