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Homeostasis - control of blood sugar level
- insulin and diabetes type 1 and type 2 diabetes - diet, obesity and body-mass
index
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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.
Sub-index for page
(a)
The need to control the blood sugar
level
(b)
The negative feedback mechanism for controlling the concentration
of blood glucose
(c)
Type 1 and 2 Diabetes - problems with insulin and how to
regulate it if need be
(d) Measures of
obesity (just one measure of healthiness and
well-being)
See
also homeostasis - water content control - urea -
kidney function
See
also homeostasis - thermoregulation and temperature control
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(a) 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.
TOP OF PAGE
and sub-index
(b) 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.
TOP OF PAGE
and sub-index
(c) 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.
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.
 Without 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).
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!).
See also
Keeping healthy - non-communicable diseases
- risk factors gcse
biology revision notes
and the 'measures
of obesity' notes below
TOP OF PAGE
and sub-index
(d) Measures of obesity (just 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.
TOP OF PAGE
and sub-index
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
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)
IGCSE revision notes control of blood sugar levels
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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
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