Oxygen-Hemoglobin Dissociation Curve

Pharmacology / Cardio & Renal / Heart Failure Drugs

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The Oxygen-hemoglobin Dissociation Curve describes the relationship between partial pressure of oxygen (PO2) and the percentage of hemoglobin saturation with oxygen. Hemoglobin, a tetramer protein in red blood cells, carries oxygen from the lungs to tissues through reversible binding. The curve has a sigmoidal shape, with the steep portion indicating rapid increase in % saturation and the flattened portion representing a plateau in % saturation. Oxygen binding to hemoglobin follows positive cooperativity, where the affinity for oxygen increases as more oxygen binds. P50 refers to the partial pressure of oxygen at which 50% of hemoglobin is saturated.

The Bohr effect describes the inverse relationship between acidity, PCO2, and hemoglobin's affinity for oxygen. A right-shift in the curve favors oxygen unloading and occurs with increased temperature, acidity, PCO2, and 2,3-DPG levels. A left-shift favors oxygen loading in the lungs, occurring when pH increases, PCO2 decreases, and temperature decreases. Fetal hemoglobin, Hemoglobin F, exhibits a left-shift for efficient oxygen transport across the placenta. Binding of carbon monoxide (CO) to hemoglobin results in a down-shift & left-shift of the curve, increasing the affinity of hemoglobin for oxygen.

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1. Raft - Hemoglobin is a protein in red blood cells that carries oxygen from the lungs to the tissues (reversible binding)
2. 4 rafts - Hemoglobin is a tetramer composed of four heme subunits with a total four O2 binding sites
3. Fraction of rafts carrying O2 - Percent hemoglobin saturation (i.e., % of heme binding sites occupied by O2 vs. total amount of binding sites)
4. S-wave - Oxy-hgb dissociation curve has a sigmoidal shape (i.e., as PO2 increases, % saturation follows a sigmoidal pattern)
5. Steep wave - Steep portion of oxy-hgb dissociation curve corresponds to a rapid increase in % saturation (i.e., from PO2 of 0 to 40 mm of Hg)
6. Flattened wave - Flattened portion of oxy-hgb dissociation curve corresponds to a plateauing in % saturation (i.e., from PO2 of 50 to 100 mm of Hg)
7. Cooperative oxygen team - The affinity of heme for oxygen follows positive cooperativity (i.e., as oxygen binding increases, affinity for oxygen increases)
8. 50 wind gust at vertical axis - P50 is the partial pressure of oxygen at which 50% of hemoglobin is saturated (i.e., ↑ P50 → ↓ affinity → right-shift; ↓ P50 → ↑ affinity → left-shift)
9. Lung vest + oxygen loading - In the lungs, hemoglobin has high affinity for oxygen → O2 loading occurs in the lungs (i.e., flat portion of oxy-hgb curve)
10. Offloading oxygen down the dock - In the tissues, hemoglobin has a lower affinity for oxygen → O2 unloading occurs in the tissues
11. Right wave + unloaded cargo - Right-shift in the oxy-hgb curve favors O2 unloading (i.e., increased P50 & reduced affinity)
12. Acid volcano + smoke cloud - ↑ acidity & ↑ PCO2 influence right-shift of oxy-hgb dissociation curve
13. Inversely running boar - The inverse relationship of PCO2 and acidity with hemoglobin’s affinity for oxygen is also known as the Bohr effect
14. Hot lava - ↑ temperature → right-shift → oxygen unloading
15. 2nd & 3rd raised sail - ↑ 2,3-DPG → binds deoxyhemoglobin → ↓ affinity → right-shift → O2 unloading
16. Left wave + tightly loaded cargo - Left-shift in the oxy-hgb curve favors O2 loading in the lungs, but is less favorable for unloading in the tissues (i.e., decreased P50 & increased affinity)
17. Basic soap + low smoke cloud - The Bohr effect dictates that left-shift will happen when pH increases and PCO2 decreases
18. Extinguished fire - ↓ temperature → left-shift → discourages oxygen unloading
19. Sinking boat with 2nd & 3rd raised sail - ↓ 2,3-DPG → left-shift → discourages O2 unloading
20. Pregnant person - Hemoglobin F, fetal hemoglobin → left-shift; ↑ affinity for O2 facilitates O2 transport across placenta
21. Cardboard cargo + smaller left wave - Carboxyhemoglobin-O2-Hgb dissociation curve
22. Stunted top of wave + left-shift - Binding of CO to Hgb → down-shift & left-shift (i.e., ↑ affinity of hemoglobin for oxygen)