4.9.2Additional lessons
Regulation of Blood Glucose — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 80 of 101
Part 1 of 4The Pancreas and Its Hormones
Islets of Langerhans
- Islets of Langerhans Clusters of endocrine cells in the pancreas that secrete hormones directly into the blood,
- as opposed to the exocrine tissue that makes digestive enzymes.
β cells
- β cells These cells detect a rise in blood glucose and secrete insulin, which lowers the glucose concentration.
α cells
- α cells These cells detect a fall in blood glucose and secrete glucagon, which raises the glucose concentration.
Target organs
- Target organs The liver is the main target of both hormones, together with muscle and fat tissue for insulin.
Part 2 of 4Actions of Insulin and Glucagon
Actions of Insulin and Glucagon
Insulin
- Insulin It makes liver, muscle and fat cells take up more glucose from the blood by increasing the number of glucose transporters in the membrane.
Glycogenesis
- Glycogenesis Insulin also stimulates the liver and muscles to convert glucose into glycogen for storage, lowering blood glucose.
Glucagon
- Glucagon It acts mainly on the liver, where it stimulates glycogenolysis, the breakdown of glycogen to glucose, which is released into the blood.
Gluconeogenesis
- Gluconeogenesis The liver can also make new glucose from non-carbohydrate sources such as amino acids, helping to raise blood glucose in fasting.
Antagonism
- Antagonism Because insulin and glucagon have opposite effects, they work as an antagonistic pair that keeps glucose near its set point.
| Condition | Hormone released | Response | Effect on glucose |
|---|---|---|---|
| After a meal | Insulin | Uptake and glycogen storage | Falls |
| Between meals | Glucagon | Glycogen breakdown | Rises |
Part 3 of 4Diabetes Mellitus
Diabetes is a failure of blood glucose control.
Type 1
- Type 1 The immune system destroys the β cells, so little or no insulin is made;
- it often begins in childhood and is treated with insulin injections.
Type 2
- Type 2 Cells respond poorly to insulin because of reduced sensitivity of receptors, and it is linked to obesity, inactivity and genetics.
Management of type 2
- Management of type 2 It is controlled by a diet low in rapidly absorbed carbohydrate, exercise, weight loss and sometimes drugs that reduce blood glucose.
Blood tests
- Blood tests Glucose tolerance tests follow how quickly blood glucose returns to normal after a drink of glucose, and slow recovery indicates diabetes.
Symptoms
- Symptoms High glucose causes thirst, frequent urination and tiredness, because glucose passes into the urine and draws water with it.
Part 4 of 4Exam Checklist & Tips
4.9.2 – Key Points for the Exam
- Insulin A hormone from β cells that lowers blood glucose.
- Glucagon A hormone from α cells that raises blood glucose.
- Glycogen A branched storage polysaccharide of glucose in liver and muscle.
- Diabetes mellitus A condition in which blood glucose is not properly controlled.
Common Mistakes
- Stating that glucagon turns glucose into glycogen; it is insulin that does so.
- Saying that insulin 'breaks down' glucose rather than causing its uptake and storage.
- Mixing the causes of type 1 (no insulin made) and type 2 (cells less responsive).
- Confusing glycogen, the storage molecule, with glucagon, the hormone.
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