4.9.2Additional lessons

Regulation of Blood Glucose — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 80 of 101

📚 IB Biology HL Hub / Topical Revision

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Part 1 of 4The Pancreas and Its Hormones

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

These cells detect a rise in blood glucose and secrete insulin, which lowers the glucose concentration.

α cells

These cells detect a fall in blood glucose and secrete glucagon, which raises the glucose concentration.

Target organs

The liver is the main target of both hormones, together with muscle and fat tissue for insulin.

Actions of Insulin and Glucagon

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

Insulin also stimulates the liver and muscles to convert glucose into glycogen for storage, lowering blood glucose.

Glucagon

It acts mainly on the liver, where it stimulates glycogenolysis, the breakdown of glycogen to glucose, which is released into the blood.

Gluconeogenesis

The liver can also make new glucose from non-carbohydrate sources such as amino acids, helping to raise blood glucose in fasting.

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

Diabetes is a failure of blood glucose control.

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

Cells respond poorly to insulin because of reduced sensitivity of receptors, and it is linked to obesity, inactivity and genetics.

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

Glucose tolerance tests follow how quickly blood glucose returns to normal after a drink of glucose, and slow recovery indicates diabetes.

Symptoms

High glucose causes thirst, frequent urination and tiredness, because glucose passes into the urine and draws water with it.

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.

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.

Last updated: 28 October 2026