Which of the following oxygen-hemoglobin dissociation curves corresponds to blood during resting (dark purple line) and during exercise ( light purple line) ?
**Core Concept**
The oxygen-hemoglobin dissociation curve is a graphical representation of the relationship between the partial pressure of oxygen (pO2) and the saturation of hemoglobin with oxygen (SaO2). During exercise, the body requires increased oxygen delivery to meet the higher metabolic demands of the muscles, leading to changes in the oxygen-hemoglobin dissociation curve.
**Why the Correct Answer is Right**
During exercise, the body increases blood flow to the muscles, which decreases the pH (becomes more acidic) and increases the temperature of the blood. These changes shift the oxygen-hemoglobin dissociation curve to the right, indicating that hemoglobin releases oxygen more easily to the tissues. This allows for increased oxygen delivery to the exercising muscles. The curve also shifts downward, reflecting the decreased affinity of hemoglobin for oxygen. In contrast, the resting curve is shifted to the left, indicating a higher affinity of hemoglobin for oxygen, which is more suitable for the lower metabolic demands of the resting state.
**Why Each Wrong Option is Incorrect**
**Option A:** This curve does not accurately represent the changes in the oxygen-hemoglobin dissociation curve during exercise. The curve is shifted to the left, indicating a higher affinity of hemoglobin for oxygen, which is not characteristic of the exercising state.
**Option B:** This curve is a normal oxygen-hemoglobin dissociation curve and does not reflect the changes that occur during exercise.
**Option C:** This curve is shifted to the right, but it does not accurately represent the downward shift that occurs during exercise.
**Clinical Pearl / High-Yield Fact**
During exercise, the body's increased demand for oxygen is met by a combination of increased cardiac output, increased blood flow to the muscles, and a rightward shift of the oxygen-hemoglobin dissociation curve.
**Correct Answer:** C