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School BIOLOGY Notes: Control of blood sugar level, insulin, diabetes

Homeostasis -  control of blood sugar level - insulin and diabetes type 1 and type 2 diabetes - diet, obesity and body-mass index

See also homeostasis - water content control - urea - kidney function

See also homeostasis - thermoregulation and temperature control

 Doc Brown's school biology revision notes: GCSE biology, IGCSE  biology, O level biology,  ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old students of biology

 This page will help you answer questions like e.g. How does the body regulate temperature?  How does the body control blood sugar level   What are glucagon and insulin?  What do they do? What is the difference between type 1 and type 2 diabetes?



Homeostasis control in the human body

Homeostasis is a word that is sometimes used to describe your bodily functions that try to maintain a stable constant internal environment including the factors listed above.

Know that internal conditions that are controlled in the body include blood sugar level.


 

Sugar level control - the need to control the concentration of blood glucose

The blood sugar levels must be adequate to provide the cells with a constant supply of energy to meet their needs.

When sugary or carbohydrate foods are digested in the small intestine, the blood sugar levels rise as the sugar is absorbed from the gut into the bloodstream.

Your normal cell metabolism uses and removes the sugar in your normal energy releasing chemistry - respiration.

If you are not doing much physical work your blood sugar level will tend to rise.

Insulin reduces the concentration of glucose in your blood.

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

Excess glucose can be to glycogen and stored in the liver and in your muscles, the glycogen which can be converted back to glucose for use during exercise.

When the glycogen stores are 'full', the excess glucose is converted to, and stored as, lipid fats.

If you are doing some demanding physical exercise your blood sugar level tends to fall as the sugar is consumed.

During exercise a number of changes take place e.g. the heart rate increases and the rate and depth of breathing increases.

These changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen for energy from respiration and also increase the rate of removal of carbon dioxide - the waste product.

Glycogen is produced and stored and released for conversion to glucose on a supply and demand basis.

If there is surplus glucose and physical activity is low, more glycogen is produced.

The more you physically exercise, the greater the glucose demand, if this exceeds what is available in the blood stream, then the glycogen reserves are called upon to fill the energy gap.

 

The blood glucose level is monitored and controlled by the pancreas which produces the hormone insulin.

The pancreas secretes enzymes that digest carbohydrates, proteins and lipid fats.

It can be dangerous if your blood sugar levels become too high or too low, so your blood sugar level is regulated by the hormone insulin made in the pancreas, which enables your body to have a regular supply of sugar for energy from respiration.

Changes in the blood glucose level are monitored by the pancreas, which produces the hormone insulin, which allows the glucose to move from the blood into the cells and stored as glycogen.

A second hormone, glucagon, is produced in the pancreas when blood glucose levels fall.

Glucagon causes glycogen to be converted back into glucose and released into the blood for respiration.

 

So, the level of glucose in the blood must be kept steady and your automatic monitoring systems keeps a check on any changes.

This is done by the pancreas using the hormones insulin and glycogen in a negative feedback cycle.

Note that the metabolism of glucose is controlled by three hormones, here it is insulin and glucagon maintaining the balanced level of glucose in the blood, but there is also the action of adrenaline on the liver in our body's 'fight or flight' response.

 


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The negative feedback mechanism for controlling the concentration of blood glucose

For glucose level read 'the blood concentration of the sugar glucose' C6H12O6

The pancreas is always checking on the concentration of glucose in the blood that flows through it.

(a) If your glucose level in the blood is too high the 1st hormone insulin is secreted by the pancreas.

After a meal the glucose concentration in the blood rises and insulin causes it to move into the cells in the body for respiration.

BUT, the insulin also causes cells in liver and muscle to convert some of the glucose into glycogen - an chemical energy store.

So, prompted by the pancreas detecting a high level of blood sugar, the insulin secreted promotes cellular uptake of glucose for respiration AND the formation of glycogen.

If the glucose concentration is too high, the pancreas secretes insulin.

Therefore, the conversion of glucose to glycogen, reduces the glucose concentration in the blood.

When the glucose level reduces, insulin is no longer secreted by the pancreas and the conversion of glucose to glycogen stops and the blood glucose level is stabilised.

(b) If the pancreas detects your blood glucose level is too low the 2nd hormone glucagon is secreted by the pancreas into the bloodstream.

Glucagon makes the liver and muscle cells convert glycogen into glucose and transported to where it is needed.

So the blood level of glucose increases - it needs to if you are engaged in vigorous exercise!

When the glucose concentration reaches an appropriate level, secretion of either insulin or glucagon stops and so does the interconversion of glycogen and glucose, thus stabilising the glucose level.

Note:

(i) Don't mix up or misspell the hormone glucagon and the 'energy store' glycogen!

(ii) Insulin hormone reduces glucose level and glucagon hormone increases glucose level.

(iii) When two effectors or substances work in opposite ways to restore something in the body to normal, they are said to be antagonistic.

The two hormones insulin and glucagon are working antagonistically because they have opposite effects, but both effects are trying to return the glucose level to normal.

The control of blood sugar levels is described below in terms of a 'homeostasis mechanism' - a 'negative feedback mechanism' using both a tabular and graphical representation of the process.

The homeostasis negative feedback system for glucose level control

(a) The homeostasis negative feedback system for too high a glucose level - insulin is added (b) The homeostasis negative feedback system for too low a glucose level - glucagon added
1. The pancreas detects the blood sugar level is too high. 1. The pancreas detects the blood sugar level is too low.
2. Insulin is secreted by the pancreas to mix with the excess glucose. 2. Glucagon is secreted by the pancreas.
3. The excess glucose is now moved from the blood into liver and muscle cells - triggered by the insulin. 3. There is too little glucose but there is glycogen stored in the liver
4. The glucose level is now reduced to the appropriate level. 4. The secreted glucagon triggers the breakdown of glycogen into glucose sugar - using the liver's energy store.
5. Overall the secreted insulin makes the liver turn the excess glucose into glycogen - effectively a store of chemical potential energy for future use. 5. Overall the glucose level is increased in the blood to meet the respiration demands of the body.
This is all automatically done by the organism's complex control systems and enables the organism e.g. your body, to maintain as near as possible the 'ideal' glucose level for healthy life!

BUT it all depends on insulin production - and there may be diabetic problems - read on

 

A simplified graphical representation of controlling the concentration of glucose in blood.

Both the hormones insulin and glucagon are made and secreted from the pancreas.


Diabetes - problems with insulin and how to regulate it if need be

Introduction

Reminders

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.

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.


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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.

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 by careful attention to diet, exercise, and by injecting insulin usually into the subcutaneous fat - 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).

 

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.

 


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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!).

 

See also Keeping healthy - non-communicable diseases - risk factors  gcse biology revision notes

and the 'measures of obesity' notes below


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

Introduction

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, but in poorer underdeveloped countries we are dealing 'underweight' people, particularly young children suffering from malnutrition.

Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.

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 https://www.vertex42.com/ExcelTemplates/bmi-chart.html)

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.

Note from 2020 on the covid-19 flue pandemic: Research has shown that obese people are more likely to be seriously ill with the virus than non-obese people - more severe fever, more likely to be hospitalised and more likely to die!

 

The waist-to-hip ratio should also be taken into consideration (see below).

 

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 https://www.healthline.com/health/waist-to-hip-ratio)

Health risk waist-to-hip ratio (women) waist-to-hip ratio (men
low less than 0.81 less than 0.96
moderate 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.


Practical work in to help develop your skills and understanding may have included the following:

demonstrating blood testing (using meters)

Be able to evaluate modern methods of treating diabetes.


Homeostasis notes index:

Homeostasis - introduction to how it functions (negative feedback systems explained)

Homeostasis - control of blood sugar level - insulin and diabetes

Homeostasis - osmoregulation, ADH, water control, urea and ion concentrations and kidney function, dialysis

Homeostasis - thermoregulation, control of temperature


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Other general HUMAN BIOLOGY revision notes

Introduction to the organisation of cells => tissues => organs => organ systems (e.g. in humans)

Examples of surfaces for the exchange of substances in animal organisms   gcse biology revision notes

See also Enzymes - section on digestion and synthesis  gcse biology revision notes

The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

The brain - what the different parts do and the dangers if damaged gcse biology revision notes

An introduction to the nervous system including the reflex arc  gcse biology revision notes

Hormone systems - Introduction to the endocrine system - adrenaline & thyroxine hormones  gcse biology revision

Hormone systems - menstrual cycle, contraception, fertility treatments  gcse biology revision notes

Respiration - aerobic and anaerobic in plants and animals.  gcse biology revision notes

Keeping healthy - communicable diseases - pathogen infections   gcse biology revision notes

Keeping healthy - non-communicable diseases - risk factors for e.g. cancers   gcse biology revision notes

Keeping healthy - diet and exercise  gcse biology revision notes

Keeping healthy - defence against pathogens, infectious diseases, vaccination, drugs, monoclonal antibodies

See also Culturing microorganisms like bacteria - testing antibiotics/antiseptics  gcse biology revision

Food tests for reducing sugars, starch, proteins and lipids  gcse biology revision notes

The eye - structure and function - correction of vision defects  gcse biology revision notes

Optics - lens types (convex, concave, uses), experiments, ray diagrams, correction of eye defects (gcse physics)


Doc Brown's School Biology Revision Notes

IGCSE revision notes control of blood sugar levels insulin diabetes KS4 biology Science notes on control of blood sugar levels insulin diabetes GCSE biology guide notes on control of blood sugar levels insulin diabetes for schools colleges academies science course tutors images pictures diagrams for control of blood sugar levels insulin diabetes science revision notes on control of blood sugar levels insulin diabetes for revising biology modules biology topics notes to help on understanding of control of blood sugar levels insulin diabetes university courses in biological science careers in science biology jobs in the pharmaceutical industry biological laboratory assistant apprenticeships technical internships in biology USA US grade 8 grade 9 grade10 AQA GCSE 9-1 biology science notes on control of blood sugar levels insulin diabetes GCSE notes on control of blood sugar levels insulin diabetes Edexcel GCSE 9-1 biology science notes on control of blood sugar levels insulin diabetes for OCR GCSE 9-1 21st century biology science notes on control of blood sugar levels insulin diabetes OCR GCSE 9-1 Gateway  biology science notes on control of blood sugar levels insulin diabetes WJEC gcse science CCEA/CEA gcse science Be able to explain how blood glucose levels are regulated by insulin and excess blood glucose is converted to glycogen in the liver The blood sugar levels – to provide the cells with a constant supply of energy. When sugary or carbohydrate foods are digested the blood sugar levels rise as the sugar is absorbed from the gut into the bloodstream. Your normal cell metabolism uses, and hence removes, the sugar in your normal energy releasing chemistry. If you are not doing much physical work your blood sugar level will tend to rise. If you are doing some demanding physical exercise your blood sugar level tend to fall as the sugar is consumed. It can be dangerous if your blood sugar levels become too high or too low, so your blood sugar level is regulated by the hormone insulin, which enables your body to have a regular supply of sugar for a secure supply of energy. During exercise a number of changes take place eg the heart rate increases and the rate and depth of breathing increases. These changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen for energy from respiration and also increase the rate of removal of carbon dioxide - the waste product. The muscles store glucose as glycogen, which can then be converted back to glucose for use during exercise. Glycogen is produced and stored and released for conversion to glucose on a supply and demand basis. If there is surplus glucose and physical activity is low, more glycogen is produced. The more you physically exercise, the greater the glucose demand, if this exceeds what is available in the blood stream, then the glycogen reserves are called upon to fill the energy gap.  blood glucose regulation This regulates the concentration of glucose (needed constantly for energy from respiration) in the blood stream. The blood sugar levels – to provide the cells with a constant supply of energy. When sugary or carbohydrate foods are digested the blood sugar levels rise as the sugar is absorbed from the gut into the bloodstream. Your cell metabolism uses and hence removes the sugar in your normal energy releasing chemistry. If you are not doing much physical work your blood sugar level will tend to rise. If you are doing some demanding physical exercise your blood sugar level tend to fall. It can be dangerous if your blood sugar levels become too high or too low, so your blood sugar level is regulated by the hormone insulin, which enables your body to have a regular supply of sugar for a secure supply of energy. Be able to explain how blood glucose levels are regulated by glucagon causing the conversion of glycogen to glucose If your glucose level in the blood is too high the 1st hormone insulin is secreted by the pancreas. Insulin makes the liver turn glucose into glycogen. Therefore, the conversion of glucose to glycogen, reduces the glucose concentration in the blood. When the glucose level reduces, insulin is no longer secreted by the pancreas and the conversion of glucose to glycogen stops and the blood glucose level is stabilised. 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. If your glucose level is too low the 2nd hormone glucagon is secreted by the pancreas. Glucagon makes the liver convert glycogen into glucose. So the blood level of glucose increases. When the glucose concentration reaches an appropriate level, secretion of glucagon stops and so does the conversion of glycogen to glucose stabilising the glucose level. Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections. In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes. You should be able to compare Type 1 and Type 2 diabetes and explain how they can be treated. You should be able to extract information and interpret data from graphs that show the effect of insulin in blood glucose levels in both people with diabetes and people without diabetes. If the blood glucose concentration is too low, the pancreas produces glucagon that causes glycogen to be converted into glucose and released into the blood. You should be able to explain how glucagon interacts with insulin in a negative feedback cycle to control blood glucose (sugar) levels in the body. Be able to evaluate information around the relationship between obesity and diabetes, and make recommendations taking into account social and ethical issues.

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