Metabolism
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Overheating after overdosing on E - and slimming by taking dinitrophenol
IET
overdosed on on Ecstasy (MDMA = methylenedioxymethamphetamine) at a rave.
She become hyperthermic, and hyperventilated.
What is happening to increase her rate of oxygen consumption and her body temperature?
The increased rate of oxygen consumption and the increase in body temperature suggest that she is oxidising more metabolic fuel - we have already seen that each litre of oxygen consumed is equivalent to 20 kJ of energy expenditure - and whether this energy expenditure is associated with physical work or not, there will be an increase in heat output from the body.
What we have to consider is how it is possible for MDMA to increase the rate at which metabolic fuels are being oxidised, so leading to excessive heat production, and hence hyperthermia.
What is the main way in which the oxidation of metabolic fuels is controlled?
The aim of oxidising metabolic fuels, and hence the aim of energy yielding metabolism, is to permit the phosphorylation of ADP to ATP, so permitting the various energy requiring processes (ion transport, muscle contraction, protein synthesis and endothermic reactions) to occur. Therefore it would seem obvious that the main controlling factor over the rate at which metabolic fuels are oxidised is the need for ATP. In turn, the need to phosphorylate ADP to ATP is signalled by the availability of ADP to be phosphorylated.
So, the main factor controlling the oxidation of metabolic fuels is the utilisation of ATP in energy requiring processes.
Remember that although the total amount of (ATP = ADP) in the body is only about 5 grams, the total amount of ATP formed from ADP, and the total amount of ATP utilised each day is about equal to body weight, some 70 kg.
How can we measure the rate at which metabolic fuels are being oxidised?
We
have seen in the jogging exercise that total energy expenditure can be measured
by measuring oxygen consumption - regardless of the mixture of fuels being oxidised,
each litre of oxygen consumed is equivalent to expenditure of 20 kJ. Therefore
we can determine the rate at which fuels are being oxidised by measuring oxygen
consumption.
We can measure oxygen consumption in the whole body, in isolated cells and tissues, and indeed in isolated subcellular compartments (the mitochondrion is the main subcellular organelle that consumes oxygen). This means that we can investigate energy metabolism and he oxidation of fuels not only in the whole body but also in isolated cells and tissues, and isolated mitochondria.
If we want to consider the oxidation of metabolic fuels linked to formation of ATP from ADP and inorganic phosphate, we need to consider the steps involved.
What are the chemical processes of oxidation and reduction?
Does oxidation necessarily involve oxygen?
Chemically, oxidation is the process of removing electrons from a molecule - either electrons alone or, more commonly with organic compounds, removal of electrons and hydrogen ions (protons), so that oxidation of organic compounds is the removal of hydrogen. The addition of oxygen (from oxygen itself or from water) is also oxidation.
Reduction is the reverse - the addition of electrons, either alone or, more commonly with organic compounds, addition of electrons and hydrogen ions (protons), so that reduction of organic compounds is the addition of hydrogen. The removal of oxygen (commonly as water) is also reduction.
The addition or removal of electrons, alone or together with hydrogen ions, does not involve oxygen.