Metabolism
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Summary - why do we need to eat and how do we survive between meals?
Total energy expenditure for a 70 kg adult is between 8 - 12 MJ /day, depending on physical activity. Approximately 70% of this is required even at rest, when not performing physical activity.
What processes account for this resting energy expenditure?
Even at rest there is some work being performed by muscles - to maintain circulation and breathing and generally maintain muscle tone.
Sodium, potassium and calcium ions are transported across cell membranes and between intracellular compartments by active transport, which is energy requiring.
There is continual breakdown of tissue proteins and replacement synthesis - both processes are energy requiring.
Many enzyme catalysed reactions are endothermic and require an input of energy.
The pie chart below shows the percentage of resting energy expenditure for different functions
