B28: Control of Blood Glucose
Blood glucose regulation with insulin and glucagon, Type 1 and Type 2 diabetes, negative feedback, and the role of the pancreas and liver for GCSE Biology.
Key Definitions
- Insulin – a hormone produced by the pancreas that lowers blood glucose by promoting glucose uptake and glycogen storage.
- Glucagon – a hormone produced by the pancreas that raises blood glucose by promoting glycogen breakdown in the liver.
- Glycogen – a polymer of glucose that is the main carbohydrate storage molecule in animals, stored in the liver and muscles.
- Type 1 diabetes – a condition where the pancreas does not produce insulin, treated with insulin injections.
- Type 2 diabetes – a condition where the body's cells do not respond properly to insulin (insulin resistance), linked to obesity.
Blood Glucose Regulation
The body needs to maintain blood glucose concentration within a narrow range. Eating raises blood glucose; exercise and fasting lower it. The pancreas monitors blood glucose and responds by releasing insulin or glucagon.
When Blood Glucose Is Too High
- The pancreas detects the rise in blood glucose.
- The pancreas secretes insulin into the blood.
- Insulin travels to the liver and muscles (target organs).
- The liver takes up glucose and converts it to glycogen for storage (glycogenesis).
- Muscle cells also take up glucose and store it as glycogen.
- Blood glucose concentration falls back to normal.
When Blood Glucose Is Too Low
- The pancreas detects the fall in blood glucose.
- The pancreas secretes glucagon into the blood.
- Glucagon travels to the liver (target organ).
- The liver breaks down glycogen back into glucose (glycogenolysis) and releases it into the blood.
- Blood glucose concentration rises back to normal.
Blood Glucose Regulation Summary
Glucose too high: Pancreas → Insulin → Liver stores glucose as glycogen → Blood glucose falls
Glucose too low: Pancreas → Glucagon → Liver breaks glycogen to glucose → Blood glucose rises
Negative Feedback in Blood Glucose Control
The regulation of blood glucose is an example of negative feedback. When blood glucose rises, insulin reduces it (reversing the change). When blood glucose falls, glucagon increases it (reversing the change). The response always opposes the direction of the original change, restoring the optimum level.
Worked Example 1 – Blood Glucose After a Meal
Question: After eating a large meal, blood glucose rises. Explain how the body brings it back to normal.
Solution: The pancreas detects the rise in blood glucose and secretes insulin into the blood. Insulin stimulates the liver and muscles to take up glucose from the blood. The liver converts excess glucose into glycogen for storage. This removes glucose from the blood, causing blood glucose concentration to fall back to normal. This is an example of negative feedback.
Worked Example 2 – Blood Glucose During Exercise
Question: During vigorous exercise, blood glucose falls. Explain how the body raises it back to normal.
Solution: The pancreas detects the fall in blood glucose and secretes glucagon into the blood. Glucagon travels to the liver, where it stimulates the breakdown of stored glycogen back into glucose. The liver releases this glucose into the blood, causing blood glucose concentration to rise back to normal. This is an example of negative feedback.
Type 1 Diabetes
- Cause: The pancreas does not produce insulin (usually because the insulin-producing cells have been destroyed by the immune system – an autoimmune disease).
- Effect: Blood glucose rises to dangerously high levels after eating because glucose cannot be taken up by cells. The kidneys excrete excess glucose in urine, causing frequent urination and thirst. Without treatment, it can be fatal.
- Treatment: Insulin injections before meals to lower blood glucose. Blood glucose must be monitored regularly. Diet and exercise also help manage the condition.
- Onset: Usually develops in childhood or young adulthood.
Worked Example 3 – Type 1 Diabetes
Question: A person with Type 1 diabetes eats a meal but does not inject insulin. Explain what happens to their blood glucose and why this is dangerous.
Solution: After the meal, blood glucose rises. In a person with Type 1 diabetes, the pancreas does not produce insulin, so the blood glucose continues to rise. Without insulin, the liver and muscles cannot take up glucose and convert it to glycogen. The kidneys excrete excess glucose in urine, causing frequent urination and dehydration (thirst). If blood glucose remains very high (hyperglycaemia), it can lead to coma and death. This is why people with Type 1 diabetes must inject insulin to help regulate their blood glucose.
Type 2 Diabetes
- Cause: The body's cells become resistant to insulin – they do not respond properly to the insulin that is produced. The pancreas may also produce less insulin over time.
- Risk factors: Strongly linked to obesity (being overweight), lack of exercise, poor diet, and genetics. More common in older adults but increasingly seen in younger people.
- Effect: Blood glucose remains too high because cells do not respond to insulin effectively.
- Treatment: Initially managed through diet, exercise, and weight loss. If these are insufficient, medication (e.g. metformin) may be prescribed. In some cases, insulin injections become necessary.
| Feature | Type 1 Diabetes | Type 2 Diabetes |
|---|---|---|
| Cause | Pancreas does not produce insulin (autoimmune) | Cells are resistant to insulin |
| Typical age of onset | Childhood / young adulthood | Adults (increasingly in younger people) |
| Risk factors | Genetics, autoimmune factors | Obesity, poor diet, lack of exercise, genetics |
| Treatment | Insulin injections | Diet, exercise, weight loss, medication, sometimes insulin |
| Prevention | Cannot be prevented | Can often be prevented or delayed through lifestyle |
Worked Example 4 – Type 2 Diabetes and Lifestyle
Question: Explain how obesity is linked to Type 2 diabetes and how lifestyle changes can help manage the condition.
Solution: Obesity is the major risk factor for Type 2 diabetes. Excess body fat, particularly around the abdomen, causes the body's cells to become resistant to insulin. This means that even though the pancreas produces insulin, the cells do not respond to it effectively, so glucose cannot be taken up from the blood and blood glucose remains too high. Lifestyle changes that can help manage Type 2 diabetes include: losing weight (reduces insulin resistance), regular exercise (muscles use glucose during activity, lowering blood glucose), and a balanced diet low in sugar and refined carbohydrates (reduces spikes in blood glucose after eating). These changes can sometimes reverse Type 2 diabetes in its early stages.
Worked Example 5 – Comparing Insulin and Glucagon
Question: Compare the roles of insulin and glucagon in blood glucose regulation.
Solution:
| Feature | Insulin | Glucagon |
|---|---|---|
| Produced by | Pancreas (beta cells) | Pancreas (alpha cells) |
| Released when | Blood glucose is too high | Blood glucose is too low |
| Effect on blood glucose | Lowers it | Raises it |
| Action on liver | Converts glucose to glycogen (storage) | Converts glycogen to glucose (release) |
| Action on muscles | Promotes glucose uptake and glycogen storage | No direct effect on muscles |
| Type of feedback | Negative feedback | Negative feedback |
Practice Questions
Foundation
Q1. Describe the role of insulin in controlling blood glucose concentration.
Show Answer
When blood glucose is too high, the pancreas secretes insulin into the blood. Insulin stimulates the liver and muscles to take up glucose from the blood. The liver converts excess glucose into glycogen for storage. This causes blood glucose concentration to fall back to normal.
Higher
Q2. Explain how glucagon raises blood glucose concentration when it falls too low.
Show Answer
When blood glucose is too low, the pancreas secretes glucagon into the blood. Glucagon travels to the liver, where it stimulates the breakdown of stored glycogen back into glucose. The liver releases this glucose into the blood, causing blood glucose concentration to rise back to normal. This is an example of negative feedback.
Foundation
Q3. Compare Type 1 and Type 2 diabetes in terms of cause and treatment.
Show Answer
Type 1: Caused by the pancreas not producing insulin (autoimmune destruction of insulin-producing cells). Treated with insulin injections. Type 2: Caused by the body's cells becoming resistant to insulin. Treated initially with diet, exercise, and weight loss, and medication if needed.
Foundation
Q4. Explain how obesity is a risk factor for Type 2 diabetes.
Show Answer
Excess body fat, particularly around the abdomen, causes the body's cells to become resistant to insulin. This means the cells do not respond effectively to insulin, so glucose cannot be taken up from the blood efficiently. Blood glucose remains too high, leading to Type 2 diabetes. Losing weight can reduce insulin resistance and help manage or even reverse the condition.
Higher
Q5. Explain how the regulation of blood glucose is an example of negative feedback.
Show Answer
Negative feedback works by reversing a change to restore the optimum. When blood glucose rises above normal, the pancreas releases insulin, which lowers blood glucose back towards normal – reversing the increase. When blood glucose falls below normal, the pancreas releases glucagon, which raises blood glucose back towards normal – reversing the decrease. In both cases, the response acts in the opposite direction to the change, which is the defining feature of negative feedback.
Exam Tips
- Always link insulin to lowering blood glucose and glucagon to raising it – do not mix these up.
- When describing blood glucose regulation, always name the pancreas as the organ that detects the change and releases the hormone.
- Type 1 = no insulin produced; Type 2 = insulin resistance. Remember this key difference.
- Type 2 diabetes is linked to obesity and lifestyle – this is a very common exam point.
- Blood glucose regulation is a classic example of negative feedback – always mention this in your answer.
🔢 Maths Skills
Mathematical Skills
Interpreting blood glucose graphs: read values from the y-axis (blood glucose concentration in mmol/L) and time from the x-axis. Identify normal range (typically 4–7 mmol/L), and describe what happens after eating (rise, peak, then return to normal via insulin). Calculate the change in blood glucose: peak minus baseline. Compare graphs for diabetic and non-diabetic individuals and explain the differences.
⚠️ Common Misconceptions
Watch Out!
1. Wrong: Type 1 diabetes is caused by lifestyle or diet. Correct: Type 1 is an autoimmune disease — the immune system destroys insulin-producing cells in the pancreas. It is not caused by diet or obesity.
2. Wrong: Type 2 diabetes always needs insulin injections. Correct: Type 2 is often managed through diet, exercise, and weight loss alone. Medication (e.g. metformin) may be needed, and insulin injections are only necessary in some cases.
✍️ 6-Mark Question
Extended Answer
6 marks: Explain blood glucose regulation and compare Type 1 and Type 2 diabetes.
Blood glucose is regulated by the pancreas through negative feedback. When blood glucose rises after a meal, the pancreas secretes insulin, which stimulates the liver and muscles to take up glucose and convert it to glycogen for storage, lowering blood glucose back to normal. When blood glucose falls (e.g. during exercise or fasting), the pancreas secretes glucagon, which stimulates the liver to break down glycogen into glucose and release it into the blood, raising blood glucose back to normal. Type 1 diabetes is caused by the destruction of insulin-producing cells in the pancreas (autoimmune), so no insulin is produced. It typically begins in childhood and is treated with insulin injections. It cannot be prevented. Type 2 diabetes is caused by insulin resistance — the body's cells do not respond properly to insulin. It is strongly linked to obesity and lifestyle, typically develops in adults, and is initially treated with diet, exercise, and weight loss. Type 2 can often be prevented or delayed through healthy lifestyle choices, whereas Type 1 cannot.
Mark scheme: 1 mark for insulin role when glucose is high; 1 mark for glucagon role when glucose is low; 1 mark for negative feedback; 1 mark for Type 1 cause and treatment; 1 mark for Type 2 cause and treatment; 1 mark for a clear comparison point (e.g. prevention, age of onset, or lifestyle link).
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
The table shows blood glucose data (mmol/L) over 3 hours after a glucose drink:
| Time (hours) | Person A (no diabetes) | Person B (untreated Type 2) |
|---|---|---|
| 0 | 5.0 | 7.8 |
| 0.5 | 7.5 | 12.1 |
| 1 | 8.2 | 14.6 |
| 1.5 | 6.4 | 13.0 |
| 2 | 5.2 | 10.5 |
| 2.5 | 4.8 | 8.8 |
| 3 | 4.9 | 7.6 |
(a) Calculate the maximum change in blood glucose for each person. (b) Explain why Person B's blood glucose takes longer to return to normal. (c) Evaluate whether Person B's data alone is enough to diagnose Type 2 diabetes — what other information would be useful?
Answers: (a) Person A: 8.2 – 5.0 = 3.2 mmol/L rise; Person B: 14.6 – 7.8 = 6.8 mmol/L rise. (b) Person B's cells are resistant to insulin, so glucose uptake is slower, and the pancreas may not produce enough insulin to cope. (c) One data set is insufficient — you would need fasting glucose tests on multiple days, HbA1c levels, information on lifestyle, BMI, and family history to confirm the diagnosis and distinguish from Type 1.
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🎬 Video Resources
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