Metabolism
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A respiratory physiology practical class - and beyond
PN had a physiology practical class on respiratory physiology, and the first exercise involved measuring the relative amounts of nitrogen, oxygen, and carbon dioxide in inhaled and exhaled air. The results were as follows:
inhaled |
exhaled |
|
| nitrogen | 78% |
78% |
| oxygen | 21% |
17% |
| carbon dioxide | 0.04% |
4.0% |
How and where has the oxygen been consumed?
Where has the carbon dioxide come from?
The oxygen has been consumed in the oxidation of metabolic fuels, mainly glucose and fatty acids, in various tissues, and the carbon dioxide is the product of that oxidation.
What are the three ways in which an organic compound may be oxidised?
removal of hydrogen
removal of electrons
addition of oxygen
What is the most common way in which metabolites are oxidised?
By removal of hydrogen onto an intermediate hydrogen carrier (or coenzyme), either NAD (nicotinamide adenine dinucleotide) or a flavin. See the exercise on overheating after overdosing on E later on for more on these coenzymes.
During the practical class it was also noticed that the exhaled air contained considerably more water vapour than inhaled air. Just over 1 mL more water was collected from exhaled air per minute than was present in the air in the laboratory.
This led to a separate experiment in which PN and several friends measured their intake of fluids, the water content of their food and the volume of urine passed each day for three days.