7.13–7.17Control of blood glucose concentration
Blood glucose concentration is monitored and controlled by the pancreas.
If the blood glucose concentration is too high, the pancreas produces the hormone insulin, which causes glucose to move from the blood into the cells. In liver and muscle cells, excess glucose is converted to glycogen for storage.
Higher tier only: if the blood glucose concentration is too low, the pancreas produces the hormone glucagon, which causes glycogen to be converted into glucose and released into the blood.
Insulin and glucagon work as a negative feedback cycle: a rise triggers insulin, which lowers it; a fall triggers glucagon, which raises it. Each hormone undoes the change that caused it to be released, which is what keeps the level roughly steady.
You should be able to interpret graphs showing the effect of insulin on blood glucose in people with and without diabetes. Read them the same way each time: find the meal, find how high the glucose rises, and find how long it takes to come back down. In a person without diabetes the peak is lower and the return is quicker, because insulin is released and acted on immediately.
Obesity is a risk factor for Type 2 diabetes, and questions here often ask for a recommendation as well as an explanation. Evaluating that means using the data on the relationship rather than assumptions about individuals, and recognising the social and ethical side: diet is shaped by cost, time and what food is available locally, so "tell people to eat better" is a weaker recommendation than one that changes what is easy to buy. Blame is not a treatment plan.
Common mistake
Insulin does not "break down" glucose. It causes glucose to move from the blood into cells, and causes the liver and muscles to convert the excess into glycogen. Glycogen and glucagon are also different things one letter apart: glycogen is the storage carbohydrate, glucagon is the hormone.
- Insulin
- the hormone produced by the pancreas when blood glucose concentration is too high, which causes glucose to move from the blood into the cells
- Glucagon
- the hormone produced by the pancreas when blood glucose concentration is too low, which causes glycogen to be converted into glucose and released into the blood
- Glycogen
- the storage carbohydrate that excess glucose is converted into in liver and muscle cells
Before you practise
- Blood glucose too high: the pancreas releases insulin, and glucose moves into cells and is stored as glycogen in the liver and muscles.
- Blood glucose too low: the pancreas releases glucagon, and glycogen is converted back to glucose.
- Type 1 diabetes is a failure to produce enough insulin, and is treated with insulin injections.
- Type 2 diabetes is the body's cells no longer responding to insulin, and is treated with a controlled diet, exercise and weight loss.
- Obesity is a risk factor for type 2 diabetes — a risk factor, not a cause.
- BMI = mass in kg ÷ (height in m)², and waist-to-hip ratio is waist ÷ hip; know which the question wants.