Topic 14.4 · Supplement
Blood Glucose Control and Type 1 Diabetes
Blood glucose concentration is controlled by two hormones working as exact opposites on the same organ — the liver — with the pancreas deciding which one to release depending on which direction the correction needs to go.
When blood glucose is too high
After a carbohydrate-containing meal, blood glucose concentration rises. In response, the pancreas secretes insulin. Insulin acts on the liver, causing it to remove glucose from the blood and convert it into glycogen for storage. As glucose is taken out of the blood and locked away as glycogen, blood glucose concentration falls back towards its set point.
When blood glucose is too low
After glucose has been used up during activity, blood glucose concentration falls. This time the pancreas secretes glucagon, which acts on the liver in the opposite direction: stored glycogen is converted back into glucose, and that glucose is released into the blood, raising blood glucose concentration back towards its set point.
Put the two mechanisms side by side and the logic is symmetrical: insulin converts glucose into glycogen and lowers blood glucose; glucagon converts glycogen back into glucose and raises it. They are exact opposites, acting on the same organ, and together they form the negative feedback loop described in general terms on the homeostasispage. It’s worth keeping the two hormone actions the right way round under exam pressure — a swapped pair reverses the whole answer even if every other detail is correct.
One further pair worth separating carefully: glucagon is a hormone secreted by the pancreas, while glycogen is the storage carbohydrate held in the liver that glucagon acts on. The two words look and sound almost identical, which is exactly why they get confused, but they are completely different substances doing completely different jobs — one is a signal, the other is what gets stored or released because of that signal.
Type 1 diabetes
In Type 1 diabetes, the body cannot produce sufficient insulin to regulate blood glucose normally. The required treatment outline is insulin replacement, commonly by injection, alongside monitoring blood glucose so that insulin can be supplied in suitable amounts. The insulin supplied this way allows blood glucose concentration to be brought back under control, including by promoting the same conversion of glucose to glycogen in the liver described above — the treatment works because it’s replacing the exact hormone the body isn’t making enough of, not because it’s doing something entirely new. Detailed study of Type 2 diabetes is not part of this syllabus requirement, so it’s worth keeping your answer focused on insulin replacement and monitoring rather than broadening into causes or treatments that belong to Type 2.