Hormonal Coordination in Humans » Diabetes

When blood glucose control fails

In the last lesson you saw how the pancreas and insulin keep blood glucose concentration steady. Diabetes is what happens when that control system does not work properly. There are two main types, and they have different causes.

In both types, the blood glucose concentration can rise to a level that is much too high. Left untreated, this is harmful to the body, so people with diabetes need to manage their condition every day.

Key terms:

• Diabetes: a disorder in which the blood glucose concentration is not controlled properly.
• Type 1 diabetes: a disorder in which the pancreas fails to produce sufficient insulin.
• Type 2 diabetes: a disorder in which the body cells no longer respond to the insulin produced by the pancreas.
• Obesity: being extremely overweight, with a very high amount of body fat.

Type 1 diabetes

In Type 1 diabetes, the pancreas fails to produce sufficient insulin. With too little insulin, glucose cannot move from the blood into the cells properly. After a meal, glucose is absorbed into the blood, but nothing brings the level back down.

The result is uncontrolled high blood glucose levels. The person's blood glucose concentration climbs and stays high.

Type 1 diabetes is normally treated with insulin injections. The injected insulin does the job the pancreas cannot do: it causes glucose to move from the blood into the cells, so the blood glucose concentration falls.

Type 2 diabetes

Type 2 diabetes is different. The pancreas still produces insulin, but the body cells no longer respond to it. Insulin is in the blood, but the cells do not take in glucose as they should, so the blood glucose concentration stays too high.

Common treatments are:

• a carbohydrate controlled diet, so that less glucose enters the blood from food;
• an exercise regime, because active muscles use up glucose.

Obesity is a risk factor for Type 2 diabetes. Remember from Lifestyle and Non-Communicable Diseases that a risk factor only raises the chance of a disease. People who are obese are more likely to develop Type 2 diabetes, but it does not mean that every obese person will get it.

Comparing Type 1 and Type 2

You should be able to compare the two types and explain how each is treated. Use this table to revise.

Feature	Type 1	Type 2
What goes wrong	The pancreas fails to produce sufficient insulin	The body cells no longer respond to insulin
Blood glucose	High, because too little insulin moves glucose into cells	High, because cells do not respond to the insulin
Normal treatment	Insulin injections	Carbohydrate controlled diet and exercise regime
Obesity	Not a risk factor given for this type	A risk factor

The key difference is where the fault is. In Type 1 the fault is in the pancreas, which does not make enough insulin. In Type 2 the fault is in the cells, which do not respond to insulin.

This also explains the treatments. Insulin injections replace the insulin that is missing in Type 1. In Type 2 the insulin is already there, so the treatments focus on the glucose itself: less glucose coming in from food, and more being used up by exercise.

Reading graphs of blood glucose

You may be given a graph showing blood glucose concentration over time after a person eats a meal containing glucose. Often the graph has two lines: one for a person without diabetes and one for a person with diabetes.

Here is a set of example data, as it might appear on a graph:

Time after the meal (hours)	Without diabetes (mg per 100 cm3)	With diabetes (mg per 100 cm3)
0	90	150
1	130	260
2	100	240
3	90	200

When you describe a graph like this, follow these steps:

1. Look at the starting values. The person with diabetes already has a higher blood glucose concentration.
2. Look at the highest point. Both lines rise after the meal, but the line for diabetes rises higher (260 compared with 130).
3. Look at the fall. Without diabetes, the level falls back to 90 within three hours. With diabetes, it stays high and falls slowly.

The line for a person without diabetes falls quickly because insulin causes glucose to move into the cells. The slow fall for a person with diabetes shows that insulin is missing or not working.

If a person with Type 1 diabetes has an insulin injection, the graph would show a faster fall in blood glucose, because the injected insulin causes glucose to move into the cells. Always quote values from the graph, with units, to support what you say.

Evaluating information about obesity and diabetes

You may be asked to look at information about obesity and diabetes and make a judgement. Obesity is a risk factor for Type 2 diabetes, so health advice often recommends a balanced diet and regular exercise. When you evaluate this kind of information, think about:

• Evidence: does the data show a link between obesity and Type 2 diabetes, and how many people were studied?
• Correlation or cause: a link in the data does not on its own prove that one thing causes the other.
• Social factors: food choices and exercise are affected by things like cost, time and what food is available.
• Ethical issues: for example, how far should a health service, or the government, tell people what to eat?

A good evaluation gives points on both sides and then reaches a conclusion using the evidence.

Exam-style question

(a) Describe the cause of Type 1 diabetes. [1 mark]

(b) A person with Type 2 diabetes produces insulin but still has a high blood glucose concentration. Explain why. [2 marks]

(c) Give two ways in which Type 2 diabetes can be treated. [2 marks]