Overview
This lecture explains the oxygen-hemoglobin dissociation curve, demonstrating how oxygen is carried and released by hemoglobin in the blood, and how various factors shift this relationship.
Oxygen Transport and Hemoglobin
- Oxygen is primarily transported in blood by binding to hemoglobin in red blood cells.
- Each hemoglobin molecule has four subunits (two alpha, two beta), each able to bind one oxygen molecule via iron centers.
- Red blood cells have about 270 million hemoglobin molecules each.
- Hemoglobin's affinity for oxygen increases as more oxygen binds, a phenomenon called cooperativity.
- The percentage of hemoglobin bound to oxygen is called saturation, measured as SpO2 (from pulse oximetry) or arterial/venous blood gas.
Partial Pressure of Oxygen
- Partial pressure of oxygen (PaO2) reflects the amount of oxygen dissolved in the blood, not bound to hemoglobin.
- PaO2 indicates how much oxygen is available for hemoglobin binding.
- Dissolved oxygen contributes minimally to total oxygen delivery compared to hemoglobin-bound oxygen.
The Oxygen-Hemoglobin Dissociation Curve
- The curve plots PaO2 (x-axis) against hemoglobin saturation (y-axis) and has an S-shape (sigmoid).
- High PaO2 leads to high saturation; as PaO2 drops, saturation falls rapidly at lower pressures.
- In oxygen-rich environments (like lungs), hemoglobin binds oxygen more tightly; in low-oxygen tissues, it releases oxygen more readily.
- The curve shows what percent of hemoglobin is saturated at a given PaO2.
Shifts in the Dissociation Curve
- Right Shift: Hemoglobin releases oxygen more easily (lower affinity).
- Caused by: increased CO2, low pH (acidosis), increased 2,3-DPG, increased temperature.
- Occurs in actively metabolizing tissues, aiding oxygen delivery.
- Left Shift: Hemoglobin binds oxygen more tightly (higher affinity).
- Caused by: decreased CO2, high pH (alkalosis), decreased 2,3-DPG, decreased temperature, fetal hemoglobin.
- Occurs in the lungs or fetal circulation, aiding oxygen uptake.
- Shifts can be caused by disease states (e.g., acidosis, sepsis) and affect oxygen binding and release.
Key Terms & Definitions
- Hemoglobin — Protein in red blood cells that carries oxygen.
- SpO2 — Peripheral oxygen saturation, the percent of hemoglobin saturated with oxygen.
- PaO2 — Partial pressure of oxygen in arterial blood.
- Cooperativity — Increasing affinity of hemoglobin for oxygen as more subunits bind O2.
- 2,3-DPG — A byproduct of glycolysis that affects hemoglobin’s oxygen affinity.
- Right Shift — Decreased hemoglobin affinity for oxygen, easier release to tissues.
- Left Shift — Increased hemoglobin affinity for oxygen, less release to tissues.
Action Items / Next Steps
- Review causes and clinical implications of right and left shifts in the dissociation curve.
- Complete assigned quiz on this lesson to test understanding.
- Review oxygen delivery calculations if unfamiliar (as referenced in the lecture).