Blood glucose regulation: WACE Year 12 Biology
“Explain how insulin and glucagon regulate blood glucose concentration by negative feedback”
Blood glucose is kept within a narrow range by two hormones from the pancreas acting on the liver. When glucose is high, insulin lowers it by promoting uptake and storage as glycogen. When glucose is low, glucagon raises it by triggering the breakdown of glycogen back to glucose. The two hormones work in opposition through negative feedback.
What this dot point is asking
SCSA wants you to name the hormones and organs involved, explain the negative feedback loop in both directions, and connect a failure of this control to diabetes. A strong answer treats the response to high and low glucose as two complementary halves of one system.
Why blood glucose must be controlled
Glucose is the main fuel for cellular respiration, so cells need a steady supply. Too little glucose starves cells, especially brain cells, of energy; too much damages tissues over time. Keeping blood glucose stable is therefore a vital example of homeostasis, controlled by the endocrine system.
The control system
The pancreas monitors blood glucose and releases hormones in response. The liver is the main effector organ, storing and releasing glucose. The two key hormones act in opposite directions:
- Insulin lowers blood glucose.
- Glucagon raises blood glucose.
Insulin and glucagon are antagonistic: they have opposite effects on the same variable. Having two opposing hormones lets the body correct blood glucose whether it is too high or too low, giving fine and rapid control in both directions.
Response to high blood glucose
After a meal, blood glucose rises. The pancreas detects this and releases insulin. Insulin causes:
- body cells to take up more glucose from the blood,
- the liver to convert glucose into glycogen for storage.
As glucose is removed from the blood, the level falls back toward normal, and insulin release decreases. This is negative feedback.
Response to low blood glucose
Between meals or during exercise, blood glucose falls. The pancreas detects this and releases glucagon. Glucagon causes:
- the liver to break down stored glycogen back into glucose,
- glucose to be released into the blood.
As glucose rises back toward normal, glucagon release decreases. Again, this is negative feedback.
Trace the negative feedback loop
A student eats a large lunch and blood glucose rises sharply. The pancreas detects the rise and secretes insulin. Insulin stimulates body cells to absorb glucose and the liver to store it as glycogen. Blood glucose falls back to the set point, the pancreas detects this, and insulin secretion slows. The variable has been returned to normal by a response that opposed the original rise.
When control fails: diabetes
Diabetes is a failure of blood glucose control. In type 1 diabetes the pancreas does not produce enough insulin, so glucose cannot be moved into cells or stored and blood glucose stays dangerously high. In type 2 diabetes cells become less responsive to insulin. Diabetes shows what happens when a negative feedback system breaks: the variable is no longer corrected and the body is harmed.
Insulin: a pancreatic hormone that lowers blood glucose. Glucagon: a pancreatic hormone that raises blood glucose. Glycogen: the storage form of glucose in the liver. Antagonistic hormones: hormones with opposite effects on the same variable.
Reading a blood glucose graph
A common exam stimulus is a graph of blood glucose concentration over several hours, showing peaks after meals and troughs between them. To interpret it, link each feature to the hormone responsible. At a peak just after eating, glucose is high, so insulin secretion is high and the line then falls as glucose is taken up and stored. In a trough between meals or during exercise, glucose is low, so glucagon secretion rises and the line climbs back toward the set point. The line oscillating gently around a steady set point, rather than drifting up or down, is the visible signature of a working negative feedback system. A line that rises after a meal and fails to come back down indicates a loss of insulin action, as in diabetes.
Why this matters for survival
Stable blood glucose keeps cells supplied with fuel regardless of when an animal last ate, letting it survive periods of fasting and bursts of activity. The insulin and glucagon loop is one of the clearest examples of negative feedback and the endocrine control of homeostasis, and the consequences of its failure in diabetes make its importance vivid.
- Swapping insulin and glucagon
- Insulin lowers glucose (after eating); glucagon raises it (when fasting).
- Saying insulin breaks down glycogen
- Insulin promotes glycogen storage; glucagon promotes its breakdown.
- Forgetting the liver
- The liver is the main store and source of glucose; the pancreas releases the hormones.
- Calling glucose control positive feedback
- It is negative feedback, opposing the change to restore the set point.
Exam-style questions
Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
WACE 2022-style7 marksDescribe the negative feedback response that returns blood glucose to its set point after it rises following a meal, naming the gland, the hormone, the target organ and the storage molecule, and explain why the response is described as negative feedback.Show worked answer →
A 7 mark describe answer needs the full ordered pathway plus the negative feedback definition.
- Stimulus
- Blood glucose rises above the set point as glucose is absorbed after a meal.
- Gland and hormone
- The pancreas detects the rise and secretes insulin into the blood.
- Target organ and effect
- Insulin acts on the liver and on body cells, making the liver and muscle take up glucose and convert it to glycogen for storage, and body cells take up and use more glucose.
- Return
- As glucose moves out of the blood, the concentration falls back toward the set point, which switches off insulin secretion.
- Why negative feedback
- The response (lowering glucose) opposes the original change (raised glucose), restoring the variable toward its set point. A response that counteracts the stimulus is negative feedback.
Markers reward the pancreas, insulin, liver as target, glycogen as the storage molecule and the explicit opposes-the-change definition.
WACE 2024-style5 marksExplain how type 1 diabetes results from a failure of blood glucose regulation, and predict what happens to blood glucose after a meal in an untreated person with type 1 diabetes.Show worked answer →
A 5 mark answer needs the cause plus the predicted blood-glucose response.
- Cause
- In type 1 diabetes the beta cells of the pancreas are destroyed, so little or no insulin is produced. Without insulin, the liver and body cells cannot take up and store glucose efficiently.
- After a meal
- Glucose is absorbed and blood glucose rises, but because there is no insulin the negative feedback loop cannot operate: glucose is not removed into cells or stored as glycogen. Blood glucose therefore stays abnormally high (hyperglycaemia) for a prolonged time instead of returning to the set point, and glucose may appear in the urine.
- Link
- This shows what happens when a negative feedback system fails: the variable is no longer corrected.
Markers reward the lack of insulin from damaged beta cells, the failure of glucose uptake or storage and the prediction of prolonged high blood glucose.