Question

In an experimental study, blood glucose levels were elevated to 2--3 times the normal and maintained at that level. What is the most likely pattern of insulin secretion in response?

• A. Rapid rise followed by a fall
• B. Gradual rise followed by a fall
• C. Remains persistently elevated
• D. Initial rise followed by sustained elevation

Hint:

Insulin response to sustained glucose is biphasic: early rapid peak followed by sustained secretion.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question tests the understanding of the "biphasic" nature of insulin secretion from pancreatic beta cells in response to a sustained glucose stimulus.
Step 2: Detailed Explanation:

First Phase: When glucose levels rise sharply, there is an immediate, rapid burst of insulin release that peaks within 3–5 minutes. This is called the "first phase" of secretion.

Mechanism of Phase 1: This phase represents the release of pre-formed insulin that is already stored in "docked" granules near the beta cell membrane, ready for immediate exocytosis.

Second Phase: If the glucose level remains high (as in this experiment), the initial burst is followed by a slight dip and then a sustained, gradual rise in insulin secretion that continues as long as the glucose remains elevated.

Mechanism of Phase 2: This phase involves the release of additional stored insulin from deeper granules as well as the new synthesis of proinsulin and insulin by the beta cells.

Clinical Significance: In Type 2 Diabetes, the first phase of insulin secretion is typically lost very early in the disease process, leading to significant post-prandial hyperglycemia.

Step 3: Final Answer:
A sustained high glucose level results in a biphasic response: an initial rapid rise followed by a sustained, secondary elevation of insulin.