Higher Insulin-Glucagon Negative Feedback in Detail

Higher Insulin-Glucagon Negative Feedback in Detail

At higher tier, you are expected to know the detailed negative feedback mechanisms for both hormones and to describe HbA1c testing:

Detailed insulin pathway:

• High blood glucose → detected by beta cells in islets of Langerhans (pancreas)
• Insulin secreted → binds to insulin receptors on liver and muscle cell surfaces
• Glycogenesis: glucose → glycogen (storage); cells also increase glucose uptake for respiration
• Blood glucose falls → beta cells reduce insulin secretion → negative feedback complete

Detailed glucagon pathway:

• Low blood glucose → detected by alpha cells in islets of Langerhans (pancreas)
• Glucagon secreted → binds to glucagon receptors on liver cells
• Glycogenolysis: glycogen → glucose; glucose released into blood
• Blood glucose rises → alpha cells reduce glucagon secretion → negative feedback complete

HbA1c testing: Glycated haemoglobin (HbA1c) is a form of haemoglobin that has glucose permanently bound to it. The proportion of HbA1c in the blood reflects the average blood glucose level over the previous 2–3 months. A high HbA1c indicates persistently elevated blood glucose — a strong indicator of poorly controlled diabetes. HbA1c testing provides a more reliable long-term measure than a single glucose reading, which can vary throughout the day.