OGT Glucose Metabolism and Physiology 2 — Questions and Answers
Question 1: What is the role of the incretin hormone GLP-1 during an oral glucose tolerance test?
- Stimulates gastric emptying
- Suppresses insulin secretion
- Enhances glucose-stimulated insulin secretion and suppresses glucagon (Correct answer)
- Promotes hepatic glucose output
Correct answer: Enhances glucose-stimulated insulin secretion and suppresses glucagon
GLP-1 (glucagon-like peptide-1) is released from intestinal L-cells during oral glucose ingestion and amplifies insulin secretion while suppressing glucagon, lowering post-meal glucose.
Question 2: Why does an oral glucose load produce a greater insulin response than the same glucose given intravenously?
- Oral absorption is faster
- The incretin effect amplifies pancreatic insulin secretion (Correct answer)
- Intravenous glucose bypasses the liver
- Oral glucose stimulates cortisol release
Correct answer: The incretin effect amplifies pancreatic insulin secretion
Gut-derived incretin hormones (GLP-1, GIP) released during oral glucose ingestion amplify insulin secretion, producing a greater response than IV glucose — known as the 'incretin effect.'
Question 3: In type 2 diabetes, impaired glucose tolerance is primarily driven by which two defects?
- Excess glucagon and low cortisol
- Insulin resistance and progressive beta-cell dysfunction (Correct answer)
- Over-secretion of insulin and low glucagon
- Renal glucose wasting and excess GLP-1
Correct answer: Insulin resistance and progressive beta-cell dysfunction
Type 2 diabetes results from a combination of peripheral insulin resistance (primarily in muscle and liver) and inadequate compensatory insulin secretion due to beta-cell dysfunction.
Question 4: Which substrate does the brain preferentially use for energy, making stable blood glucose critical?
- Fatty acids
- Ketone bodies
- Glucose (Correct answer)
- Amino acids
Correct answer: Glucose
Under normal conditions the brain relies almost exclusively on glucose as its energy substrate, requiring tightly regulated blood glucose levels.
Question 5: What is the normal renal glucose threshold at which glucosuria (glucose in urine) appears?
- ~100 mg/dL
- ~140 mg/dL
- ~180 mg/dL (Correct answer)
- ~250 mg/dL
Correct answer: ~180 mg/dL
Glucose appears in the urine when plasma glucose exceeds approximately 180 mg/dL, the renal tubular reabsorption threshold.
Question 6: Insulin resistance in peripheral tissues results in which metabolic consequence during an OGTT?
- Rapid return to fasting glucose levels
- Prolonged elevation of post-load plasma glucose (Correct answer)
- Decreased glucagon secretion
- Enhanced GLP-1 release
Correct answer: Prolonged elevation of post-load plasma glucose
When peripheral tissues resist insulin's glucose-uptake signal, post-load glucose remains elevated longer, resulting in an abnormal OGTT curve.
OGT Glucose Metabolism and Physiology 2
What is the role of the incretin hormone GLP-1 during an oral glucose tolerance test?