In COPD there is chronic hypoxia that is particularly obvious in vascular tissues such as the lips or nail beds (cyanosis). Poorly perfused areas exposed to chronic hypoxia have decreased metabolic energy for tissue maintenance and repair. Which of the following is an important reason for this?
|A||Increased hexokinase activity owing to increased oxidative phosphorylation|
|B||Increased ethanol formation form pyruvate on changing from anaerobic to aerobic metabolism|
|C||Increased glucose utilization via the pentose phosphate pathway on changing from anaerobic to aerobic metabolism|
|D||Decreased ATP generation and increased glucose utilization on changing from aerobic to anaerobic metabolism.|
a. The exposure of tissues to chronic hypoxia makes them rely more on anaerobic metabolism for the generation of energy as ATP and other high-energy phosphates.
b. Most tissues except for red blood cells can metabolize glucose under anaerobic or aerobic conditions (red blood cells do not have mitochondria for electron transport and must rely on other tissues to generate glucose back from lactate).
c. In most tissues, a switch from aerobic to anaerobic metabolism greatly increases glucose utilization and decreases energy production.
d. A reduction of glucose utilization under anaerobic conditions in bacteria is known as the Pasteur effect after its discoverer, Under aerobic conditions, the cell can produce a net gain in moles of ATP formed per mole of glucose utilized that can be as high as 18 times that produced under anaerobic conditions.
e. Thus the cell generates more energy and requires less glucose under aerobic conditions.
f. Such increased ATP concentrations, together with the release of citrate from the citric acid cycle under aerobic conditions, allosterically inhibit the key regulatory enzyme of the glycolytic pathway, phosphofructokinase. Decreased phosphofructokinase activity decreases metabolism of glucose by glycolysis.