Control of Blood Glucose and Diabetes

Your blood carries glucose, a sugar your cells use as fuel for respiration. The amount of glucose in the blood must be kept within a narrow range: too high or too low and cells stop working properly.

The organ that monitors and controls blood glucose concentration is the pancreas. It constantly checks how much glucose is dissolved in the blood and responds by releasing hormones — chemical messengers carried in the blood — that push the level back to normal.

Blood glucose concentration is monitored and controlled by the pancreas.

Glucose levels rise and fall throughout the day:

• After a meal containing carbohydrate, glucose is absorbed from the gut into the blood, so the level rises.
• During exercise or between meals, cells use glucose for respiration, so the level falls.

The pancreas detects these changes and corrects them. The two hormones it uses are insulin (lowers blood glucose) and glucagon (raises blood glucose). Insulin is required for everyone; glucagon is Higher Tier only.

When blood glucose is too high, the pancreas detects this and produces the hormone insulin.

Insulin causes glucose to move out of the blood and into the body's cells. In two places — the liver and the muscles — any excess glucose is then converted into glycogen, an insoluble storage molecule, and held in store. The result is that the blood glucose concentration falls back toward normal.

When blood glucose is too high, the pancreas releases insulin, which causes glucose to move from the blood into cells. In the liver and muscles, excess glucose is converted to glycogen for storage.

Two effects of insulin lower the blood glucose level:

Effect of insulin	What happens	Result
Glucose into cells	Glucose moves from blood into body cells	Cells use it for respiration
Glycogen storage	Liver and muscle cells convert excess glucose to glycogen	Glucose removed from blood and stored

Do not confuse the spellings. Glucose is the sugar that circulates in the blood. Glycogen is the larger storage molecule made from many glucose units, kept in the liver and muscles. Insulin is the hormone that triggers the change — it is not the store itself.

Trace what happens, step by step, when you eat a meal rich in carbohydrate.

So the correcting hormone here is insulin, and the two things it does are: move glucose into cells, and store the excess as glycogen in the liver and muscles.

An exam question may give a graph of blood glucose over time after a meal. In a person without diabetes, the level rises after eating, then drops back to normal within a couple of hours as insulin acts. A sharp rise that stays high and does not come back down is a sign that insulin is missing or not working — the basis of diabetes, covered later in this lesson.

(Higher Tier only — the role of glucagon and the full negative-feedback loop below are required only for the Higher Tier paper.)

Insulin handles the "too high" case. The opposite problem — blood glucose too low — needs the opposite hormone.

When blood glucose is too low, the pancreas produces a second hormone, glucagon. Glucagon causes glycogen stored in the liver to be converted back into glucose, which is then released into the blood. This raises the blood glucose concentration back toward normal.

(Higher Tier only) When blood glucose is too low, the pancreas releases glucagon, which causes glycogen to be converted back into glucose and released into the blood.

The two hormones do opposite jobs, both made by the pancreas:

Hormone	Released when glucose is	Effect on glucose	Net result
Insulin	Too high	Glucose → cells; excess glucose → glycogen (stored)	Blood glucose falls
Glucagon	Too low	Glycogen → glucose (released into blood)	Blood glucose rises

A common slip is to mix up the two hormone names because they look alike. A memory hook: gluc-A-gon Adds glucose to the blood; insulin puts it into cells.

(Higher Tier only — this complete loop, showing how glucagon interacts with insulin, is a Higher Tier requirement.)

Insulin and glucagon work together in a negative feedback cycle: whenever the level moves away from normal, the body acts to reverse the change and bring it back. Trace the response to low blood glucose — for example, after exercise has used up glucose:

Step by step for the low-glucose case:

Because each hormone reverses the change that triggered it, the level is held steady around the norm. That is what "negative" means in negative feedback: the response opposes the original change.

Diabetes is a condition in which blood glucose cannot be controlled properly. There are two types, with different causes.

• Type 1 diabetes — the pancreas produces little or no insulin. Without enough insulin, glucose is not moved into cells or stored, so blood glucose stays uncontrolled and high. It is normally treated with insulin injections (taken so the level drops after meals), alongside attention to diet and exercise.
• Type 2 diabetes — the pancreas still makes insulin, but the body cells no longer respond to it. Glucose therefore stays in the blood. Obesity is a risk factor. It is commonly treated with a carbohydrate-controlled diet and an exercise regime.

Feature	Type 1	Type 2
Cause	Pancreas produces little or no insulin	Body cells no longer respond to insulin
Insulin present?	Insufficient / none	Present, but ineffective
Typical onset	Often in childhood / younger people	More common later in life
Risk factor named by AQA	—	Obesity
Usual treatment	Insulin injections	Carbohydrate-controlled diet + exercise

Type 1 = not enough insulin (treat with injections). Type 2 = cells ignore the insulin (treat with diet and exercise; obesity is a risk factor).

(Extra context — not required by AQA 8461.) Type 2 diabetes is sometimes managed with tablets such as metformin when diet and exercise are not enough. AQA only requires the diet-and-exercise treatment.

1. Saying insulin raises blood glucose

Insulin lowers blood glucose: it moves glucose from the blood into cells and triggers storage as glycogen in the liver and muscles. The hormone that raises blood glucose is glucagon (Higher Tier).

2. Confusing glucose with glycogen

Glucose is the soluble sugar carried in the blood. Glycogen is the insoluble store made from many glucose molecules, kept in the liver and muscles. Write the correct word — markers treat them as different terms.

3. Mixing up the two hormone names

Insulin and glucagon are both made by the pancreas but do opposite jobs. Glucagon raises blood glucose by turning glycogen back into glucose; insulin lowers it. Mixing the names reverses the whole answer.

4. Confusing the causes of Type 1 and Type 2

Type 1 = the pancreas does not make enough insulin. Type 2 = the cells stop responding to the insulin that is made. Stating that Type 2 means "no insulin is produced" is wrong.

5. Matching the wrong treatment to the type

Type 1 is treated with insulin injections because the body lacks insulin. Type 2 is usually managed with a carbohydrate-controlled diet and exercise. Do not assume every diabetic uses injections.

6. Forgetting glycogen storage happens in the liver and muscles

When insulin acts, excess glucose is converted to glycogen specifically in the liver and muscle cells. Name these locations rather than saying glucose is just "stored somewhere".