Glucose is taken in a test tube in the form of solution. Next, a vial of insulin is added to the contents of test tube. After about a couple of hour, a suitable test could detect no change in the amount of glucose in test tube. How is this possible?
Insulin has nothing to act upon inside the test tube, meaning, insulin can only do its job when there are tissues to respond to its signals.
It is a key player in glucose homeostasis where its primary function is to initiate the uptake of glucose into cells when it senses high levels of glucose in peripheral circulation.
Normal blood glucose concentration is around ~
In your test tube, you have just insulin, glucose and nothing else. Since insulin acts on other tissues, you will likely see no change in the amount of glucose in the test tube.