Below is an example of a Glucose Tolerance Test (GTT) Prior to taking the GTT, p

Question

Below is an example of a Glucose Tolerance Test (GTT)

Prior to taking the GTT, patients are required to do an overnight fast of at least 8 hours. However, the level of blood/plasma glucose during an overnight fast is not 0. What is a possible explanation for how blood glucose levels are maintained during this time period?

a. Within minutes of not eating, liver immediately starts gluconeogenesis and releases glucose into the blood.

b. Adipose tissue breaks down fat and converts them to glucose to be released into the blood.

c. Liver metabolizes glycogen stores into glucose which is then released into the blood.

d. All organs and all cells in the body shift consumption from glucose to ketone bodies as an energy source.

e. ALL OF THE ABOVE. (That is, all answers above are possible)

Explanation / Answer

The correct option is................a. Within minutes of not eating, liver immediately starts gluconeogenesis and releases glucose into the blood.

Without taking night dinner, the liver glycogen levels fall dramatically. During night liver supplies the major portion of glucose needed, by breakdown of glycogen into glucose. By morning, there wont be any liver glycogen available due to night fasting. In order to check the hypoglycemia due to low blood glucose levels during fasting, gluconeogenesis takes place in liver. The glucose generated from non-carbohydrate substrates such as lactate, pyruvate, glycerol and amino acids have been converted to glucose through gluconeogenesis within liver. This helps in maintaining stable blood glucose level during fasting. This process is not under the control of insulin but under the control of stress hormones such as glucagon, adrenalin and growth hormone.

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