How does the body keep blood glucose within a safe range?
Explain how insulin and glucagon regulate blood glucose by negative feedback, and how diabetes disrupts this
The pancreas regulates blood glucose by negative feedback: insulin lowers high glucose and glucagon raises low glucose; diabetes results from faulty insulin production or response.
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What this dot point is asking
You need to name the control gland and hormones, explain the two opposing feedback responses, and explain the two main types of diabetes as a failure of this control.
The variable and its control centre
Blood glucose concentration must be kept within a narrow range. Too high (hyperglycaemia) damages tissues and changes water balance; too low (hypoglycaemia) starves cells, especially brain cells, of energy.
The control centre is the pancreas, which monitors blood glucose and releases two opposing hormones from its islet cells: insulin and glucagon. Their main target is the liver.
Response to high blood glucose
After a meal, blood glucose rises above the set point:
- The pancreas detects the rise and releases insulin into the blood.
- Insulin makes liver and muscle cells take up glucose and convert it to glycogen for storage (and promotes glucose use by cells).
- Blood glucose falls back toward the set point, and insulin release decreases.
Response to low blood glucose
Between meals or during exercise, blood glucose falls below the set point:
- The pancreas detects the fall and releases glucagon.
- Glucagon makes the liver break stored glycogen back down into glucose, which is released into the blood.
- Blood glucose rises back toward the set point, and glucagon release decreases.
Diabetes
Diabetes mellitus is a failure of blood glucose regulation, so glucose stays dangerously high.
- Type 1 diabetes: the pancreas cannot produce enough (or any) insulin, often because the insulin-producing cells are destroyed by the immune system. It usually appears early in life and is managed with insulin injections.
- Type 2 diabetes: the pancreas produces insulin, but body cells become resistant and no longer respond to it properly. It is linked to lifestyle and diet and is often managed with diet, exercise and medication.
In both, glucose cannot be taken into cells effectively, so blood glucose remains high.
Exam-style practice questions
Practice questions written in the style of SACE Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2018 SACE Stage 22 marksCompare the action of insulin and glucagon in the regulation of blood sugar.Show worked answer →
A comparison needs a point about each hormone, showing they have opposite effects.
Insulin is released when blood glucose is high. It lowers blood glucose by stimulating body cells to take up glucose and by promoting the conversion of glucose to glycogen for storage in the liver.
Glucagon is released when blood glucose is low. It raises blood glucose by stimulating the liver to break down glycogen into glucose, which is released into the blood. The two hormones therefore act antagonistically to keep blood glucose within a stable range.
2018 SACE Stage 22 marksDescribe how a hormonal imbalance can result in diabetes.Show worked answer →
For 2 marks, link the hormone problem to high blood glucose.
In type 1 diabetes the pancreas produces little or no insulin, so body cells cannot take up glucose effectively and blood glucose stays high. In type 2 diabetes the pancreas may produce insulin but the target cells do not respond properly to it (insulin resistance).
In either case, the negative feedback control of blood glucose fails, so blood glucose remains elevated after eating, which is the characteristic of diabetes.