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Homeostasis: 3. Diabetes type 1 and diabetes type 2 - problems with insulin and how to make sure your blood sugar levels are safely normal

Doc Brown's Biology exam study revision notes

There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index of notes on homeostasis: Blood sugar level control, insulin, diabetes

(3) Diabetes - health issues with insulin production and how to regulate it if need be



Insulin reduces the concentration of glucose in your blood - triggers the conversion of glucose into glycogen - your principal chemical potential energy store.

Lack of insulin can lead to dangerously high glucose levels in your blood.

See (1) The need to control the blood sugar level - health issues

What is diabetes?

Diabetes conditions occur in people whose body, for one reason or another, does not produce enough insulin to adequately control the level of glucose in the bloodstream.

Diabetes is the failure of the homeostasis control system described in the previous section i.e. the negative feedback system based on the hormones insulin and glucagon - diagram below.

Type 1 Diabetes - caused by insulin deficiency

Type 1 diabetes is a disease in which a person’s blood glucose concentration may rise to a high level because the pancreas does not produce enough of the hormone insulin.

What causes type 1 diabetes? The insulin producing cells are destroyed - this can be due to an autoimmune condition in which the immune system mistakenly attacks the body's own healthy cells.

Type 1 diabetes is caused by a lack of insulin, the hormone which controls the level of glucose in the blood - too little may be produced or non at all - a potentially dangerous situation.

Without insulin secretion the blood glucose level to rise to potentially lethal levels.

graph of glucose levels after taking a sugar drink type 1 diabetic non-diabetic gcse biology igcseWithout insulin, the body's cells are unable to utilise glucose, whose level becomes dangerously high and excreted in the urine.

The graph on the right compares the glucose concentration in the blood after a Type 1 diabetic and a non-diabetic person after each is given a sugary drink.

The diabetic, not producing insulin, has no control over the glucose level which rises well above that normally required. It remains too high, but can be lowered if insulin is injected into the body.

The non-diabetic produces insulin from the pancreas in response to the rising concentration of glucose, which goes well above normal. The glucose level then falls back to normal as the body's cells take up the glucose (respiration or glycogen formation).

Note that if the supply of glucose is inadequate, the body's cells use fat and protein as alternative energy supplies.

If the diabetes is not controlled, a person can lose weight and lead to kidney failure and death.

Type 1 diabetes may be controlled partially by careful attention to diet and exercise, BUT injection of insulin, usually into the subcutaneous fat is required- insulin therapy must always be applied to type 1 diabetes patients.

Type 1 diabetes can be controlled by two strategies, and both may be required ..

There is NO CURE for Type 1 diabetes and it cannot be prevented.

(i) Avoid too much sugary foods and carbohydrates in the diet, sugars in particular, will cause a rapid rise in glucose levels which is difficult to remove without the presence of sufficient insulin - but diet management is not enough to cope with Type 1 diabetes.

(ii) Insulin therapy - injecting insulin, perhaps several times a day at meal times, which will make the liver and muscles remove excess glucose from the digested food - this makes sure the excess glucose is converted to glycogen, reducing the concentration in the blood.

This is an inconvenient, but very effective way, of keeping the blood sugar level in check.

The insulin is usually injected into the subcutaneous fatty tissue just under the skin.

You cannot take insulin orally as a pill or tablet because the enzymes in your stomach break it down before it can reach the bloodstream.

The amount of insulin required varies from individual to another - it depends on the body mass, diet and exercise they take - injecting too much insulin could lead to too low a level of glucose in the blood.

In Type 1 diabetes, the level of physical activity and diet affect the amount of insulin required.

The amount of insulin required by injection depends on the person's diet and level of physical activity.

A diabetic should minimise food rich in simple carbohydrates like glucose which can cause quite a rapid increase in blood sugar.

As well as controlling carbohydrate intake, taking regular exercise helps to use up some of the excess glucose from the blood.

It is dangerous to inject too much insulin because that could lead to dangerously low levels of glucose.

Insulin injections can greatly help diabetics in providing the necessary insulin but it can never be as successful as a properly functioning normal pancreas and diabetics can suffer from long-term health problems.

A healthy balanced diet, regular eating and regular exercise will both help to keep a diabetic in good health and minimise the amount of insulin needed.

Diabetics can have a pancreas transplant which, if successful, can theoretically avoid the need for insulin, but there is always the danger tissue rejection and costly immunosuppressive drugs must be taken (with the added complication of serious side-effects).

Monitoring your blood sugar levels

You can do a blood sugar level check by doing a finger-prick test, or by using an electronic blood sugar monitor called a flash glucose monitor or CGM.

You can do this several times a day – helping you keep an eye on your levels as you go about your life and help you work out what to eat and how much insulin medication to take.

Footnote on source of insulin

Insulin was once extracted from the pancreas of a pig or cow, but human insulin is now made genetic engineering and doesn't give the side effects experienced from patients using animal insulin.

I remember a class debate on the merits and ethical issues concerning the use of genetic modification (GM) engineering. A diabetic in the class took to task another student trying to take the 'moral high ground' in arguing how wrong it was to use GM for medical purposes (or any other purpose - on the grounds it was interfering with nature). So, can I please point out the millions of diabetic patients around the world whose lives are so much more improved by a 'slow release' genetic modification of the hormone insulin.

Type 2 Diabetes - caused by insulin resistance

Type 2 diabetes is caused by a person becoming resistant to their own insulin.

The type 2 diabetes condition is

(i) When the pancreas doesn't make enough insulin to enable the body to respond effectively to rising glucose levels.

(ii) The person has become resistant to insulin so the body doesn't even respond appropriately to any of the hormone insulin present - its as if the body's cells have lost their sensitivity to changes

and both will cause the blood sugar level to rise to potentially lethal levels.

Test for Type 2 diabetes

One test is to ask the patient to refrain from eating and drinking for ~10 hours and the glucose level in the blood measured.

The patient is then given glucose and their blood reanalysed for its concentration 2 hours later.

If the patient's tolerance to glucose is lowered, the glucose will be above an acceptable level.

Type 2 diabetes can be controlled by eating a healthy balanced diet, regular eating, regular exercise and losing weight if necessary.

Being overweight increases your chance of developing type 2 diabetes, obesity is considered to be potentially a major risk factor in the onset of diabetes disease.

As well as a poor diet of too much fat and carbohydrates (often 'fast food'), lack of exercise can be another contributing factor.

Sadly, in the UK, there are rising numbers of diabetes Type 2 cases being recognised.

It is estimated, in the UK, about 3 in 10 children are obese.

Type 2 diabetes patients should make an effort to control the amount of carbohydrates in their food and take regular exercise - both strategies can help reduce the glucose sugar level in the blood.

Some Type 2 diabetics take medication or insulin to help control this diabetic condition - but insulin therapy is more associated with type 1 diabetes.


There is some correlation between obesity and Type 2 diabetes.

Obese people have an increased risk to develop type 2 diabetes.

There are two ratio indexes used as a measure of obesity.

They are both described in detail in the last section on this page.

Obese people (BMI > 30) do run the risk of developing type 2 diabetes,

and if their BMI is over 30, then action should be taken.

Body Mass Index (BMI) = (body mass in kg) / (height in m)2

Footnote on the food and drinks industry

Many drinks, processed foods and snacks contain too much sugar, but they are very popular.

Governments, with some success, have tried to get manufactures to reduce the sugar content in food.

How, and should we, enforce changes on manufacturers to control our diet?

Isn't there an ethical responsibility for manufacturers to produce more healthy food?

Cafes, restaurants and school/factory canteens should provide healthy food that contributes to a healthy diet.

One idea is to impose a 'sugar tax' on the cost of sugar rich foods or directly on food companies that produce them.

However, such a tax might disproportionately affect the poorest people in society, where statistics show they are the most at risk from diabetes - some of the most unhealthy food is also the cheapest and most children like 'snacky' foods too (as do many of us adults, but it is occasionally a relatively harmful lifestyle choice!).

Measures of obesity  (just one measure of healthiness and well-being)

However, people outside the limits of the indexes described below, i.e. overweight or obese, could be more susceptible to diabetes than the average person.


There is no such thing as the 'perfect weight', we come in all shapes and sizes, but there are limits within which we should be to be healthy!

In the medical profession, a doctor can't just simply that somebody is overweight, without reference to some kind of statistical index, usually by one/both of the ratios described below.

Equally healthy people can have quite different weights, but there are some reasonably good indicators as to when your weight is not what it should be 'ideally'.

In rich developed countries we are often dealing with 'overweight' people eating too much rich fatty food.

The negative health effects of being overweight and obese, many of which can be fatal include: high blood pressure (hypertension), high LDL cholesterol or high levels of triglycerides, Type 2 diabetes, coronary heart disease, stroke and gallbladder disease.

The Body Mass Index

The body mass index is a 'rough' guide to help the medical profession decide whether you are underweight, normal, overweight or obese - based on your height and height.

The higher your BMI the more fat you are carrying - but not necessarily unhealthily.

Body Mass Index (BMI) = (body mass in kg) / (height in m)2

When measured, you then consult a table of BMI values to se where you fit in!

Table of BMI values (from

Body mass index Weight description
less than 18.5 underweight
18.5 to 24.9 normal
25.0 to 29.9 overweight
30.0 to 40.0 moderately obese
over 40.0 very obese

If you eat too much fatty sugary foods and don't take enough exercise, most people will put on weight and too much of it. You are taking in too much energy rich food for your daily needs.

The excess energy releasing food is stored as fat and gives you a raised BMI value.

Having a higher than normal BMI value increases your risk of developing type 2 diabetes.

Note of caution: Having a high BMI is not always unhealthy e.g. athletes train hard to build up extra muscle which is heavier than fat, so they will tend to have higher than 'normal' BMI values and would not be classed as overweight.

The waist-to-hip ratio

Where the body stores fat is quite important.

If a lot of fat is stored around the abdomen you get a 'fat tummy' and this is associated with an increased risk of developing type 2 diabetes - hence the importance of diet and exercise.

Comparing the circumferences of waist and hips is another measure of whether you are 'overweight' and concentrates around one area where we can accumulate to much fat - the 'tummy'.

waist-to-hip ratio = circumference of waist (cm) / circumference of hips (cm)

The higher your waist-to-hip ratio the more fatty tissue you are carrying around the middle of your body.

When measured, you then consult a table of BMI values to se where you fit in!

Table of waste-to-hip ratios (from

Health risk

waist-to-hip ratio (women)

waist-to-hip ratio (men


less than 0.81

less than 0.96


0.81 to 0.85

0.96 to 1.00

high (overweight)

over 0.86

over 1.00

If you are female and your waist-to-hip ratio is over 0.86 you are classed as overweight.

If you are male and your waist-to-hip ratio is over 1.00 you are classed as overweight.

If you are above the moderate waist-to-hip ratio values you are carrying too much fat around your 'middle' - referred to as abdominal obesity.

Having a higher than normal waist-to-hip ratio increases your risk of developing type 2 diabetes.

Keywords, phrases and learning objectives for this part on ?

This page will help you answer questions like e.g. What are glucagon and insulin?  What do they do in your body? What is the difference between type 1 diabetes and type 2 diabetes?

Know what diabetes is and the difference between type 1 diabetes and type 2 diabetes.

Know diabetes is about insulin production (deficiency) and resulting health issues and insulin is required to ensure blood sugar levels are safely normal.

Know that diabetes treatments and strategies include insulin therapy injection, avoiding sugary foods, monitoring blood sugar levels e.g. with a finger prick test and an electronic flash glucose monitor.



INDEX of biology notes on homeostasis: Control of blood sugar level - insulin and diabetes


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