Blood glucose regulation - TCE Biology (Tasmania)
“Analyse glucose regulation in humans, including stimulus-response models, feedback loops and the associated hormones (insulin and glucagon) and organ structures”
Blood glucose is kept within a narrow range (about 4 to 8 mmol/L) by negative feedback. The pancreas acts as the receptor and control centre. When blood glucose rises, the pancreas releases insulin, which makes body cells take up glucose and the liver store it as glycogen, so glucose falls. When blood glucose falls, the pancreas releases glucagon, which makes the liver break glycogen down into glucose and release it into the blood, so glucose rises. In diabetes, this regulation fails because of a lack of insulin (type 1) or a poor response to it (type 2).
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What this dot point is asking
Glucose regulation is part of criterion 6 (Section C of the TASC exam). The external assessment specifications include the pancreas as receptor, the actions of insulin and glucagon, the effectors (cells take up glucose; the liver converts glucose to glycogen) and a general understanding of diabetes. GLUT transporters and naming the alpha and beta cells of the islets are not required.
Why blood glucose must be controlled
Glucose is the main fuel for cellular respiration, and the brain depends on a steady supply. Too little glucose (hypoglycaemia) deprives cells of energy; too much (hyperglycaemia) over long periods damages blood vessels, nerves and organs.
The feedback loops
Blood glucose rises (after a meal)
- Stimulus: blood glucose rises above the normal range.
- Receptor and control centre: the pancreas detects the rise.
- Message: the pancreas releases insulin into the blood.
- Effectors: liver, muscle and other body cells.
- Response: cells take up more glucose and use it in respiration; the liver and muscles convert glucose into glycogen for storage.
- Result: blood glucose falls back to normal and insulin release decreases.
Blood glucose falls (between meals, during exercise)
- Stimulus: blood glucose falls below the normal range.
- Receptor and control centre: the pancreas detects the fall.
- Message: the pancreas releases glucagon into the blood.
- Effector: the liver.
- Response: the liver breaks down glycogen into glucose and releases it into the blood.
- Result: blood glucose rises back to normal and glucagon release decreases.
Glucose is the sugar in the blood. Glycogen is the storage form in the liver and muscles. Glucagon is the hormone that triggers glycogen breakdown. TASC's 2025 assessment report noted that students often confused glycogen and glucagon, and sometimes reversed the roles of the liver and pancreas.
Diabetes (general understanding)
- Type 1 diabetes: the immune system destroys the insulin-producing cells of the pancreas, so little or no insulin is produced. It usually begins in childhood or young adulthood and is treated with insulin.
- Type 2 diabetes: body cells become less responsive to insulin (insulin resistance), and insulin production may also fall. It is linked to genetics and lifestyle factors such as physical inactivity and excess weight, and is managed with diet, exercise and medication.
In both types, glucose is not taken up efficiently from the blood, so blood glucose stays high after meals.
Two people drink the same glucose solution
Person A's blood glucose rises to about 8 mmol/L after 30 minutes and returns to about 5 mmol/L by 2 hours. Person B's rises to about 14 mmol/L and is still above 11 mmol/L at 2 hours.
- Person A: normal regulation; insulin released in response to the rise brings glucose back to the normal range.
- Person B: glucose stays high, consistent with diabetes: either too little insulin (type 1) or cells not responding to it (type 2).
- Link to the model: in Person B the negative feedback loop is not returning the variable to its set point.
Marker's note: describe the trend with values from the graph, then explain it with the hormone and effector.
- Naming the hypothalamus as the control centre
- For blood glucose it is the pancreas.
- Saying insulin breaks down glucose
- Insulin causes cells to take up glucose and the liver to store it as glycogen.
- Calling the pancreas an effector
- In the TASC model the pancreas is the receptor and control centre; the liver and body cells are the effectors.
Exam-style questions
Questions in the style of TASC 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.
Original5 marksExplain how blood glucose concentration is returned to normal after a meal rich in carbohydrate.Show worked answer →
One mark for each step, in order.
- Blood glucose rises above the normal range after the meal (stimulus).
- The pancreas detects the rise and releases the hormone insulin into the blood.
- Insulin travels in the blood to its target cells (effectors): liver, muscle and other body cells.
- Body cells take up more glucose from the blood and use it in respiration; the liver (and muscle) convert glucose to glycogen for storage.
- Blood glucose falls back towards the normal range, so the stimulus is reduced and less insulin is released (negative feedback).
Original4 marksDistinguish between type 1 and type 2 diabetes in terms of their cause and how each affects the regulation of blood glucose.Show worked answer →
Two marks for each type.
Type 1. The body's immune system destroys the insulin-producing cells of the pancreas, so little or no insulin is made. After a meal, cells cannot take up enough glucose and blood glucose stays high. It is managed with insulin injections or a pump.
Type 2. The body's cells respond poorly to insulin (insulin resistance), and the pancreas may not make enough to compensate. Glucose is not taken up efficiently, so blood glucose stays high. It is linked to lifestyle and genetic factors and is managed with diet, exercise and medication, sometimes including insulin.