Blood glucose regulation
CIE A-Level BiologyΒ· 15.3(d), 15.3(e)Β· 15 min read
1. Why Regulate Blood Glucose?β β ββββ± 3 min
Healthy blood glucose is maintained between 4β6 mmol dmβ»Β³. Glucose is the primary respiratory substrate for most cells, especially brain cells which cannot use alternative fuels efficiently. Hypoglycaemia (low glucose) deprives cells of energy, causing confusion, coma and death. Hyperglycaemia (high glucose) lowers blood water potential, causing osmotic cell damage and long-term harm to blood vessels and nerves.
Normoglycaemia
The stable normal range of blood glucose concentration maintained by homeostatic mechanisms
Example:
A healthy person after an 8-hour fast has normoglycaemia between 4β6 mmol dmβ»Β³
Explain why untreated hyperglycaemia leads to dehydration.
- 1
High blood glucose increases the solute concentration of blood plasma, which lowers its water potential.
- 2
Water moves out of body cells into the blood plasma by osmosis, down the water potential gradient.
- 3
Increased blood volume causes the kidneys to produce larger volumes of urine to excrete excess water.
Exam tip:
Always reference water potential changes when explaining effects of high blood glucose β this is a common CIE marking point.
2. Response to High Blood Glucoseβ β ββββ± 5 min
After eating a carbohydrate-rich meal, blood glucose rises above the normal range. This change is detected by Ξ²-cells (beta cells) in the islets of Langerhans, endocrine tissue in the pancreas. Ξ²-cells secrete insulin into the bloodstream.
Insulin
A hormone that lowers blood glucose by increasing glucose uptake, utilisation and storage in target tissues
Increases number of GLUT4 glucose transporters on cell surfaces, raising glucose uptake
Activates glycogenesis (glucose β glycogen) for storage in liver and muscle
Increases glycolysis (glucose breakdown for respiration)
Inhibits glycogenolysis and gluconeogenesis (glucose production)
Describe how the body corrects a rise in blood glucose after a meal.
- 1
A rise in blood glucose above normal is detected by Ξ²-cells in the pancreatic islets of Langerhans.
- 2
Ξ²-cells secrete increased amounts of insulin into the bloodstream, which travels to target tissues (liver, muscle, adipose).
- 3
Insulin binds to cell surface receptors, triggering intracellular responses that increase glucose uptake and storage, lowering blood glucose.
- 4
Once blood glucose returns to normal, negative feedback reduces insulin secretion to stop the response.
3. Response to Low Blood Glucoseβ β β βββ± 4 min
When blood glucose falls below normal (between meals, after exercise), the change is detected by Ξ±-cells (alpha cells) in the pancreatic islets of Langerhans. Ξ±-cells secrete the hormone glucagon, whose main target tissue is the liver.
Glucagon
A hormone that raises blood glucose by activating glycogen breakdown and glucose synthesis in the liver
Activates glycogenolysis: breakdown of stored glycogen into glucose
Activates gluconeogenesis: synthesis of glucose from non-carbohydrate sources
Inhibits glycogenesis to prevent glucose storage
How do insulin and glucagon work together to maintain stable blood glucose?
- 1
Both are secreted by the pancreas in response to changes in blood glucose, acting via negative feedback.
- 2
Insulin (from Ξ²-cells when glucose is high) lowers blood glucose, while glucagon (from Ξ±-cells when glucose is low) raises blood glucose.
- 3
They have antagonistic (opposing) effects that counteract each other to keep glucose within a narrow normal range.
4. Diabetes Mellitusβ β β βββ± 3 min
Diabetes mellitus is a disorder where blood glucose regulation fails, causing chronic hyperglycaemia. There are two distinct main types, which CIE examiners frequently ask to compare:
Feature | Type 1 Diabetes | Type 2 Diabetes |
|---|---|---|
Cause | Autoimmune destruction of Ξ²-cells, no insulin produced | Target cell insulin resistance, Ξ²-cell dysfunction over time |
Typical onset | Childhood/early adolescence | Adulthood, linked to obesity |
Treatment | Insulin injections + controlled diet | Diet/exercise, oral drugs, eventual insulin |
Prevalence | ~10% of all diabetes cases | ~90% of all diabetes cases |
Why is glucose found in the urine of people with untreated diabetes?
- 1
Blood glucose rises far above the maximum reabsorption threshold of kidney nephrons.
- 2
Excess glucose cannot be reabsorbed from the filtrate back into the blood, so it remains in urine.
- 3
Glucose lowers the water potential of the filtrate, so more water remains in urine, causing increased urine output.
Exam tip:
Practice drawing a full negative feedback diagram for blood glucose regulation, this is a common 5-6 mark question.
5. Common Pitfalls
Wrong move:
Confusing glycogenesis, glycogenolysis and gluconeogenesis
Why:
Similar terms are often mixed up in exam answers
Correct move:
Remember the suffix: genesis = creation: glycogenesis = create glycogen; lysis = breakdown: glycogenolysis = break down glycogen; gluconeogenesis = create new glucose from non-carbs
Wrong move:
Stating glucagon is produced by the liver
Why:
Confusing the site of secretion with the target tissue
Correct move:
Glucagon is secreted by Ξ±-cells in the pancreas; the liver is its main target tissue
Wrong move:
Claiming Type 2 diabetes is caused by insufficient insulin
Why:
Early Type 2 diabetes is not caused by low insulin levels
Correct move:
Type 2 diabetes is caused by insulin resistance (target cells do not respond to insulin); insulin levels may even be elevated initially
Wrong move:
Forgetting to mention negative feedback
Why:
Blood glucose regulation is a classic example of negative feedback, which is always a marking point
Correct move:
Always state that once blood glucose returns to normal, hormone secretion is reduced to stop the response
Wrong move:
Only mentioning insulin when describing glucose regulation
Why:
Students often forget the role of glucagon in raising blood glucose
Correct move:
Always include both insulin (lowering) and glucagon (raising) in any full description of glucose regulation
6. Quick Reference Cheatsheet
Process / Condition | Key fact | Control |
|---|---|---|
Glycogenesis | Glucose β glycogen (storage) | Activated by insulin |
Glycogenolysis | Glycogen β glucose | Activated by glucagon, adrenaline |
Gluconeogenesis | Glucose from non-carbs | Activated by glucagon |
Type 1 Diabetes | No insulin produced | Treated with insulin injections |
Type 2 Diabetes | Insulin resistance | Managed with diet/exercise |
Normal range | 4β6 mmol dmβ»Β³ | Negative feedback |
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2022 Β· 11
Multiple choice on insulin action
- 2023 Β· 22
Essay on glucose regulation
- 2024 Β· 13
Compare Type 1 and 2 diabetes
Going deeper
What's Next
Blood glucose regulation is one of the most frequently tested examples of homeostasis in CIE A-Level Biology. Mastering this topic builds a strong foundation for understanding other homeostatic control systems, which follow the same core principles of negative feedback, hormone action and cell signalling. Extended response questions often ask for comparisons between different homeostatic mechanisms, so understanding the key patterns here will help you answer those questions effectively. The next topics build on this knowledge to explore other key homeostatic systems in the human body.