Info
🌱 來自: Huppert’s Notes
Gas exchange🚧 施工中
Gas exchange
• Oxygen:
- Oxygen is transported in two forms: 1) Dissolved in blood; 2) Bound to Hgb (most important/majority)
• Hemoglobin: 2α2β subunits; heme moiety with iron-containing porphyrin
• O2 capacity refers to the maximum amount of O2 that can be bound to Hgb
- Upper limit of how much O2 can be carried by the blood
- Must be measured at 100% saturation
• O2 content refers to the total O2 carried in blood = Hgb-bound O2 + dissolved O2 = (1.34 × [Hgb] × % Sat) + (0.0031 + PaO2)
- Oxygen–Hgb dissociation curve is SIGMOIDAL (Figure 2.6)
FIGURE 2.6: Oxygen–hemoglobin dissociation curve. “Right shifts” in the curve allow oxygen to be released from hemoglobin more easily, whereas “left shifts” cause oxygen to bind hemoglobin more tightly. O2 = oxygen; P50 = oxygen tension at which hemoglobin is 50% saturated; PCO2 = partial pressure of carbon dioxide; H+ = hydrogen ions; 2,3-DPG = 2,3-diphosphoglyceric acid
• Shift L: Increased O2 affinity = ↓ PCO2, ↓ 2,3 DPG, ↓Exercise, ↓Temperature, ↓H+, Fetal Hb, CO
• Shift R: Lower O2 affinity = ↑ PCO2, Altitude, ↑ 2,3 DPG, Exercise, ↑ Temperature, (CADET), ↑H+
• Carbon dioxide:
- Carbon dioxide transport: 1) HCO3 formed by carbonic anhydrase (~90% of CO2), 2) Dissolved CO2, 3) Carbaminohemoglobin (i.e., Hgb-CO2)
- Hgb–CO2 dissociation curve is LINEAR
• In lungs, Hgb is oxygenated → Hgb–CO2 dissociation curve shifts right + down → CO2 unloads (Haldane effect)
• Variations/disruptions in Hgb function:
- Methemoglobinemia (Met-Hgb): Involves iron in Hgb converting from ferrous [Fe2+] to ferric [Fe3+] form, making it unable to bind oxygen. Medication culprits include dapsone, nitrates. Tx: Methylene blue.
- Carboxyhemoglobin (CO-Hgb): Product of reaction between carbon monoxide and hemoglobin; CO releases more slowly than CO2 from Hgb. Symptoms: Tiredness, dizziness, unconsciousness, death. Tx: Nonrebreather, hyperbaric chamber. Involve toxicology.