Oxygen Transport and Hemoglobin Dissociation Curve - Anatomy and Physiology

1. Arterial blood is 98 percent saturated and venous blood returning at rest is 75 percent saturated. By how many percentage points did saturation fall in the tissues?

   23 percentage points ($98 - 75$), meaning roughly one quarter of the bound O2 is unloaded at rest.

2. What is the physiological advantage of the flat upper plateau of the oxygen-hemoglobin curve?

   Saturation stays near maximal even if alveolar PO2 falls moderately, for example at mild altitude, protecting O2 loading.

3. Which four changes shift the oxygen-hemoglobin dissociation curve to the right?

   Increased PCO2, increased H+ (lower pH), increased temperature, and increased 2,3-BPG.

4. Approximately what percentage of oxygen in arterial blood is carried bound to hemoglobin?

   About 98 percent. Only about 1.5 to 2 percent travels dissolved in plasma.

5. What is the P50 of hemoglobin, and what is its approximate normal value in adults?

   The PO2 at which hemoglobin is 50 percent saturated, about 27 mmHg. A higher P50 indicates a right shift (lower affinity).

6. What is the Bohr effect?

   The decrease in hemoglobin's O2 affinity caused by higher CO2 and H+, which promotes O2 unloading in active tissues.

7. How does fetal hemoglobin's O2 affinity compare with adult hemoglobin, and why does it matter?

   It is higher (curve shifted left), which lets fetal blood take up O2 from maternal blood across the placenta.

8. Blood contains 15 g/dL hemoglobin, and each gram binds 1.34 mL O2 when fully saturated. What is the maximum O2 bound per dL?

   About 20.1 mL O2 per dL, because $15 \times 1.34 = 20.1$.

9. Why is the oxygen-hemoglobin dissociation curve sigmoid (S-shaped)?

   Cooperative binding: each O2 that binds increases hemoglobin's affinity for the next O2 molecule.

10. How many O2 molecules can one hemoglobin molecule carry?

    Four, one bound to the iron of each of its four heme groups.

11. How does carbon monoxide impair oxygen transport?

    It binds heme with far higher affinity than O2, reducing carrying capacity, and shifts the curve left so remaining O2 is unloaded less readily.

12. What does a rightward shift of the oxygen-hemoglobin curve mean for oxygen delivery?

    Hemoglobin's affinity for O2 decreases, so more O2 is unloaded to tissues at a given PO2.

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