Muscle Myoglobin

As described in chapter 12, myoglobin is a red pigment found exclusively in striated muscle cells. In particular, slow-twitch, aerobically respiring skeletal fibers and cardiac muscle cells are rich in myoglobin. Myoglobin is similar to hemoglobin, but it has one heme rather than four; therefore, it can combine with only one molecule of oxygen.

Myoglobin has a higher affinity for oxygen than does hemoglobin, and its dissociation curve is therefore to the left of the oxyhemoglobin dissociation curve (fig. 16.37). The shape of the myoglobin curve is also different from the oxyhemoglobin

0 20 40 60 80 100 120

Po2 (mmHg)

Figure 16.37 A comparison of the dissociation curves for hemoglobin and myoglobin. Myoglobin is an oxygen-binding pigment in skeletal muscles. At the PO2 of venous blood, the myoglobin retains almost all of its oxygen, indicating that it has a higher affinity than hemoglobin for oxygen. The myoglobin, however, does release its oxygen at the very low PO2 values found inside the mitochondria.

0 20 40 60 80 100 120

Po2 (mmHg)

Figure 16.37 A comparison of the dissociation curves for hemoglobin and myoglobin. Myoglobin is an oxygen-binding pigment in skeletal muscles. At the PO2 of venous blood, the myoglobin retains almost all of its oxygen, indicating that it has a higher affinity than hemoglobin for oxygen. The myoglobin, however, does release its oxygen at the very low PO2 values found inside the mitochondria.

dissociation curve. The myoglobin curve is rectangular, indicating that oxygen will be released only when the PO2 becomes very low.

Since the PO2 in mitochondria is very low (because oxygen is incorporated into water here), myoglobin may act as a "go-between" in the transfer of oxygen from blood to the mitochondria within muscle cells. Myoglobin may also have an oxygen-storage function, which is of particular importance in the heart. During diastole, when the coronary blood flow is greatest, myoglobin can load up with oxygen. This stored oxygen can then be released during systole, when the coronary arteries are squeezed closed by the contracting myocardium.

Test Yourself Before You Continue

1. Use a graph to illustrate the effects of Po on the loading and unloading reactions.

2. Draw an oxyhemoglobin dissociation curve and label the POj values for arterial and venous blood under resting conditions. Use this graph to show the changes in unloading that occur during exercise.

3. Explain how changes in pH and temperature affect oxygen transport and state when such changes occur.

4. Explain how a person who is anemic or a person at high altitude could have an increase in the percent unloading of oxygen by hemoglobin.

Was this article helpful?

0 0
Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

Get My Free Ebook


Post a comment