3. Physiology
        3.9. Metabolism and Nutrition
3.9.1. Metabolism

Metabolism

Units

Calorie (cal)

1 cal = energy required to raise the temperature of 1g of water from 15 degree C to 16 degree C.

1 Cal = 1 kcal = 1000 cal

Covertion to Joule

1 calorie = 4.1868 J

 

Glucose conversion

1mole of glucose
= 180gram

Glucose level of
180mg/dL = 10mmol/L

Caloric value

Carbohydrate = 4.1 kcal/g

Fat = 9.3 kcal/g

Protein = 4.1 kcal/g
* Outside body, when measured with bomb calorimeter
--> protein = 5.3 kcal/g
* Difference is due to end product being urea and other nitrogenous compounds

Respiratory quotient

Respiratory quotient (RQ) = the ratio of CO2 produced to O2 consumed in steady state.

Respiratory exchange ratio (R) = the ratio of CO2 produced to O2 consumed at any given time, whether or not equilibrium has been reached.

RQ

RQ of carbohydrate = 1.0

RQ of fat = 0.7 (because extra O2 is needed for the formation of H2O)

RQ of protein = 0.82 (average value)

RQ of an organ

... is determined by the metabolic process occurring in them.

RQ of brain = 0.97 to 0.99
* Carbohydrate is the main, but not the only fuel

RQ of stomach = negative
* Negative CO2 output because of acid secretion

Metabolic rate

Isotonic muscle contraction is about 50% efficient.

Essentially all isometric contraction appears as heat and no work is done.

Measurement

Basal metabolic rate is measured:

Measured indirectly.

O2 consumption is measured using oxygen-filled spirometer and a CO2 absorber.

Conversion: 4.82 kcal/L of O2 consumed
* [WG21:p284]

Correlates well with body surface area

Factors affecting metabolic rate

Specific dynamic action

[WG21:p284]

In providing 100 cal worth of energy, metabolic rate increase by:

Energy transfer

High energy phosphate compounds

The most important - adenosine triphosphate (ATP)

Others include:

Hydrogen acceptors

After picking up hydrogen

NADP+ and NADPH

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