Controlling the internal environment

3.1 Controlling the
internal environment
Think of some of the reactions that could be taking place inside
your body:
ÿ digestion of food
ÿ growth and repair
ÿ release of energy from the food you eat
ÿ manufacture of hormones that control development
ÿ destruction of wastes that are toxic to your cells.
Most of these reactions will produce heat as a by-product. Yet if the
temperature inside your body was to increase, everything would
stop. A very important part of homeostasis is temperature control.
Body temperature
Responding to change
Most of the time your body temperature is between 37°C and 38°C.
You are kept warm by all the activity occurring inside your body
(metabolism) which produces heat. Because you can maintain a
constant body temperature you are said to be endothermic. All
other mammals and birds are also endothermic.
Your temperature will vary slightly depending on the food you have
eaten, the amount of exercise you are doing, and the time of day.
Your temperature is at its lowest when you are asleep (especially at
night) and highest when you are awake and active. A ‘thermostat’ in
your brain sends messages to parts of your body that respond to a
change in your body temperature.
Oh, it’s hot!
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We usually respond to a warm environment by wearing lighter
clothing, by having more skin exposed to the air and by moving
into the shade. These are voluntary responses. However, there are
also involuntary responses from your body:
ÿ Heat from your body causes sweat (which is mostly water) to
evaporate. It takes a lot of heat to evaporate a small amount of
water, therefore this is a very effective cooling mechanism. One
litre of sweat, when it evaporates, removes about 209 kJ of heat
from the body. The rate at which heat is lost by evaporation will
depend on the difference in temperature between the body and
the surrounding air, and the relative humidity of the air.
ÿ Blood capillaries close to the skin dilate (increase in diameter) so
that more blood (carrying heat) can reach the skin surface. This
is called vasodilation. The extra blood near the surface makes
your skin more red.
Excess heat is carried by the blood to the skin surface where it is
used to evaporate the sweat. When you produce very large amounts
of heat—for example, when you exercise—then you have to get rid
of that heat more rapidly so that you can maintain a constant
body temperature.
figure 3.1 When you are running a lot
of heat is produced in your body. Heat is
lost from blood close to the body surface
and through the evaporation of sweat.
Responding to change
149
SCIENCE
in
actiON
> The meltdown man
Mark Dorrity was a keen athlete who included a 4 km run in his daily exercise routine as well as a
1 km swim about three times each week. He was fit. In 1988 he entered an 8 km fun run in Wagga
Wagga, NSW. The run was cancelled by the organisers because the temperature was expected to
be 42°C. Mark decided to do the run anyway. Unfortunately, this turned out to be a serious error
of judgment. During the run Mark collapsed suffering heat exhaustion and dehydration. He was
rushed to hospital where doctors battled to reduce his soaring body temperature which reached a
dangerous 42.8°C. Mark survived the ordeal, but he did not come away unscathed.
Normal human body temperature is 37°C and when the body’s temperature becomes too high, blood
proteins become denatured and the blood coagulates (this is similar to the curdling of boiled milk).
When this happens the blood can no longer pass through the capillaries and so it cannot deliver
nutrients to the body cells or remove wastes from those cells. All parts of the body can be affected.
Mark might have sustained less damage if he had taken frequent drinks during the run, but he
became dehydrated and did not replace the lost fluid, so his blood became viscous (sticky and thick).
This reduced the blood flow through blood vessels and further reduced nutrient flow and waste
removal. This caused Mark’s heart to stop and, as a result, he also sustained some brain damage.
In addition, the overheating of Mark’s muscle cells resulted in a rare condition known as
‘rhabdomyolysis’. This is an extreme condition in which muscles become fatigued and dehydrated; the
muscle cells literally liquefy and die. Dead cells cannot be revived. The dead muscle tissue in Mark’s
left leg became gangrenous and was amputated. The dying muscle cells released toxic chemicals into
the bloodstream and caused kidney failure. Overall Mark was in a coma for three months.
RADIATIONFROM
THE3UN
CONDUCTION
FROMATMOSPHERE
EXHALEDAIR
HEAT
PRODUCTION
BY
METABOLISM
EVAPORATION
OFSWEAT
CONDUCTIONAND
RADIATIONTO
ENVIRONMENT
URINEANDFAECES
CONDUCTION
FROMGROUND
CONDUCTION
TOGROUND
figure 3.2 To maintain a constant body temperature
there must be a balance between the loss of heat to the
surrounding air and the heat gained by the body.
figure 3.3 Mark Dorrity made the mistake of running in around 42°C
heat; his muscles melted and he suffered kidney failure and rhabdomyolysis
which resulted in the loss of his leg and brain damage.
150
Responding to change
SCIENCE
work
EXPERIMENT
3 .1
> Investigation of heat exchange
with the atmosphere
Safety
Aim
To investigate factors that influence
the rate of heat exchange.
➤ Be careful when pouring
hot water.
Method
Materials
!
➤ electric jug
➤ 6 x thermometers
➤ 6 x 100 mL beakers
➤ water from the fridge
➤ marker pen or labels
Responding to change
1 Label five beakers, each with a different temperature: 4°C, 10°C, 20°C, 30°C and 40°C.
2 Into the beaker marked 4°C add 80 mL of water from the fridge. Using the thermometer measure
the temperature immediately and record the data.
3 Fill the remaining beakers each with 80 mL of water of the required temperature. You could do this
by using a mixture of water from the fridge, tap water and water heated using the electric jug.
4 Measure and record the temperatures in each beaker immediately. These are the temperatures for
time zero (0 min).
5 Record the temperature in each of the beakers every 2 minutes from the time when the water was
poured into the beaker for at least 20 min. You should have 11 records for each beaker
Note: If you have access to them, temperature probes could be used for this investigation.
Results
Present your results in a table and as a graph.
Discussion
chapter
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Have a look at the results obtained by other groups in the class. Discuss any major differences
and possible reasons for them. Describe and explain any patterns you can see in the data.
Relate the results you have collected to the impact on the human body of moving from one
environment to another.
Extension
Devise experiments to test the following:
➤ The effect of sweating on the rate of cooling.
➤ The rate of cooling in different relative humidities.
➤ The insulating effects of different types of clothing.
Now it’s cold!
If your body is surrounded by air or water that is a lot cooler than
your body temperature you will lose heat quickly. Our voluntary
response is to put on more layers of clothes to cover our skin. There
are also involuntary responses from your body:
ÿ Shivering is the rapid contraction and relaxation of your muscles;
any activity of the muscles produces heat inside your body.
ÿ Vasoconstriction is the constriction (reduction in diameter) of
the blood vessels near the surface of the skin, thus the amount
of heat carried to the skin is reduced. If the external temperature
is very cold, the blood flow to the extremities (fingers, toes, nose
and ears) will be reduced further and you can lose feeling in
them—your toes and fingers go numb.
Have you ever noticed that it is
easier to catch lizards on a cool
morning? Many animals, including
reptiles, are not able to keep their
body temperature constant. Instead
they have to rely on heat from the
environment to keep them warm;
they are ectothermic. On cool
mornings lizards sit on rocks sunning
themselves. They are not trying to
get a suntan. They are trying to raise
their body temperature enough so
that they can start hunting for food.
Responding to change
151
HAIR
ÿ Goose bumps result from the hairs on the body trying to stand
on end to trap a layer of air around the body as insulation. This
works well in animals with a lot of hair and in birds with a layer
of feathers; however, it is not very effective in humans.
HAIRFOLLICLE
MUSCLEATTACHEDTO
THESKINANDTOTHE
HAIRFOLLICLE
GOOSEBUMP
MUSCLE
CONTRACTS
figure 3.4 When you get cold, a
muscle attached to your skin and to
a hair contracts,
causing the hair to
contra
‘standd on end
end’. The bump on the skin
that we call a ‘goose bump’ is the
position of the contracted muscle.
"ODYTEMPERATURE #
Table 3.1
Body temperature (˚C)
POSSUM
45–46
40+
38+
PLATYPUS
Some of the effects of a change in internal temperature.
CAT
37
LIZARD
%XTERNALTEMPERATURE #
figure 3.5 The effect of external
temperature on the body temperatures
of different animals. The cat, possum
and platypus are endothermic. The
lizard
is ectothermic.
liz
35
32–34
28–30
25–27
Effect
death
hyperthermia
confusion, coma
fever, flushed appearance, excessive
sweating
normal
shivering
hypothermia
tiredness, confusion, loss of feeling,
paleness
coma, respiratory failure
death
The amazing filters
At the end of the story about Mark Dorrity it mentioned that his
kidneys failed. The kidneys are important organs in homeostasis. They
control both the salt and water balance within the body. You take in
water and salts through food and drink. The body also manufactures
about 350 mL of water per day as a product of cellular respiration. You
lose some water in the air you breathe out. You lose water and salts
through sweat and in the faeces you produce; however, most salts and
water are lost through urine. The body needs to balance its losses and
gains. The kidneys are the organs that produce urine and therefore can
control the amount of water and salt lost.
152
Responding to change
About a quarter of the blood that is pumped from the heart is sent to
the kidneys; this adds up to about 50 L/hour. Within the kidney are
millions of microscopic filters that remove harmful wastes (such as
urea), salts and water from the blood. The kidney returns to the
blood the salts, glucose and water needed by the body. Wastes, excess
salts and excess water pass from the kidneys into the bladder where
they are stored before they are released from the body as urine.
7ATERLOSS
52).%
37%!4
&!%#%3
"2%!4(
7ATERGAIN
%!4).'
$2).+).'
7ATERBALANCEUPSET
CELLSCANNOTWORKPROPERLY
DILUTEBLOOD
!$( IN
BLOODSTREAM
MOSTWATERIS
ABSORBEDBACK
INTOBLOOD
7ATERBALANCEMUSTBEKEPT
WITHINTHISNARROWRANGE
figure 3.6 Gains and losses of water by the body must be balanced. If
there is too much or too little water in the body it will not function correctly.
NO!$(IN
BLOODSTREAM
LITTLEWATERIS
ABSORBEDBACK
INTOBLOOD
CONCENTRATEDURINE
SMALLAMOUNT
DILUTEURINE
LARGEAMOUNT
Responding to change
CONCENTRATED
BLOOD
figure 3.7 The volume of urine excreted
by the kidneys is controlled by a hormone
(ADH) released from the pituitary gland.
Table 3.2
Substance Amount in blood (%) Amount in urine (%)
90–93
0.1
0.37
0.03
95
0
0.6
2
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water
glucose
chloride (salt)
urea
If you drink a lot more water than your body requires, large
amounts of light-coloured, dilute urine will be produced. If
your water intake is inadequate you produce dark-coloured,
concentrated urine. The amount of urine produced is controlled
by the antidiuretic hormone (ADH) which is released from the
pituitary gland.
The kidneys work so efficiently that we can survive with just one
fully functioning kidney. Failure of both kidneys is a disaster
because the blood can no longer be filtered and wastes accumulate
in the body. People with kidney failure have to undergo dialysis for
many hours each day and their only hope for long-term survival
is a kidney transplant.
A continuous energy supply
To provide energy for your body throughout the day your cells need
a continuous supply of glucose for cellular respiration. Too much
glucose makes your blood thick, meaning that it can move only
slowly through your blood vessels. Too little glucose makes you
Even when you are thinking you
are using up energy or burning up
kilojoules. Different activities burn
up different amounts of kilojoules.
Sitting in the classroom for just
over an hour uses up 100 kJ.
Responding to change
153
A FOODTAKEN
INTOBODY
BLOODGLUCOSE
LEVELRISES
NORMALLEVEL
OFBLOOD
GLUCOSE
PANCREAS
RELEASES
INSULININTO
THEBLOOD
'LYCOGENISFORMEDINTHE
LIVERFROMEXCESSGLUCOSE
4HISREMOVESGLUCOSE
FROMTHEBLOOD
B
EXERCISEUSESGLUCOSE
BLOODGLUCOSE
LEVELFALLS
NORMAL
LEVELOF
BLOOD
GLUCOSE
PANCREAS
RELEASES
GLUCAGON
INTOTHEBLOOD
'LYCOGENINTHELIVERIS
BROKENDOWN4HISADDS
GLUCOSETOTHEBLOOD
figure 3.8 (a) The body responds to
increased glucose levels by producing
the hormone insulin. Insulin causes
glucose to be removed from the blood
and stored for later use in the form of
glycogen. (b) When glucose levels in the
blood fall the hormone glucagon allows
the glucose stores to be accessed and
glucose is returned to the blood.
Worksheet 3.1
Recent advances in treating
diabetes describes many different
approaches to the treatment and
cure of this disease.
154
Responding to change
feel dizzy because you have insufficient energy. Glucose is carried
around the body dissolved in the blood plasma. It enters the blood
from the digestive tract and is absorbed by most body cells. Despite
this intake and usage, the levels in the blood do not alter very much
and a concentration of about 0.8–1 mg/mL is maintained. The
steady concentration is due to the action of two hormones: insulin
and glucagon. These hormones are made by groups of specialised
cells in the pancreas, called ‘islets’. When blood glucose levels
increase after eating, the pancreas releases insulin. Insulin causes
the liver and muscles to extract glucose from the bloodstream and
store it as glycogen. This lowers the glucose levels in the blood.
When glucose is taken from the bloodstream during activity, the
pancreas responds by releasing glucagon, which has the opposite
effect to insulin. So, by the controlled release of the two hormones,
the glucose levels can be kept fairly constant. This maintaining of a
stable internal environment is an example of homeostasis.
Diabetes
People with the disease diabetes are either not able to produce
insulin or their tissues are not able to respond to it. There is more
than one type of disorder known as diabetes. In type 1 diabetes,
the pancreas cannot produce insulin because the islets have been
destroyed by the body’s own immune system. This is referred to as
an ‘auto-immune reaction’. Why this happens is not known, but
it has nothing to do with lifestyle. There is a strong family link,
but a trigger such as a viral infection causes the immune system to
destroy the islets in the pancreas. Type 1 diabetes can occur at any
age, but it usually affects children and young adults. Just 10–15% of
all people with diabetes have type 1 diabetes.
Type 2 diabetes is a lifestyle disease and is strongly associated with
high blood pressure, high cholesterol and the classic apple-shaped
body where there is extra weight around the waist. The pancreas
of people with type 2 diabetes is making insulin, but their tissues
are resistant to it. The body responds by making more insulin.
Eventually it can’t make enough to maintain the glucose balance.
There is no single cause for developing type 2 diabetes, however,
there are well-known risk factors some of which are related to
heredity and cannot be changed. Other factors such as weight, level
of physical activity, the type of food we eat, and smoking are under
our control. Overweight or obese people have extra fat around their
internal organs. This fat is dynamic, releasing into the bloodstream
fatty acids that interfere with the uptake of insulin by the cells.
Also if large amounts of fat are stored in muscle then the muscle
cells become less sensitive to insulin. Failure of the cells to respond
to insulin leads to abnormal levels of glucose in the blood which
eventually destroys the pancreas and insulin production stops.
Type 2 diabetes is often controlled by diet, at least in the early
stages. However, in the later stages insulin has to be injected.
Diabetes can lead to serious complications such as blindness,
cardiovascular disease, stroke, kidney failure, and gangrene in
the legs.
SCIENCE
work
activity
3.2
> Balancing glucose
The blood glucose levels of two people after
consuming the same quantity of glucose.
Time after drinking
juice (min)
Questions
1 Which person suffers from diabetes? Explain.
2 Rapid-acting insulin can begin to work within
1 h. At what time should the diabetic person
have taken the injection?
3 What causes the non-diabetic person’s blood
glucose levels to fall?
4 Why did the diabetic person’s blood glucose
levels eventually fall?
5 What are the target cells for insulin?
6 Why do diabetics inject insulin into fat deposits
rather than directly into the bloodstream?
(Consider the rate of absorption.)
Questions
3 .1
1 What is homeostasis?
2 a Why is it important that our body temperature
remains constant?
b Describe two involuntary reactions that help
to keep our body temperature down.
c Describe two involuntary reactions that help
to keep our body temperature from dropping
too low.
3 Explain why sweating is such an efficient way of
losing body heat.
4 How do the kidneys contribute to homeostasis?
5 a How does glucose first enter the bloodstream?
b Why is it important that glucose is not
excreted?
6 a What is the major difference between type 1
and type 2 diabetes?
b What can you do to reduce your chances of
developing type 2 diabetes?
0
15
30
45
60
75
90
105
120
Blood glucose level
(mg/100 mL )
Matthew
Elly
86
110
140
115
90
80
84
85
85
85
125
170
190
210
210
200
180
145
Challenge Questions
Responding to change
Table 3.3
3 .1
7 What differences do you think might be in the
data in table 3.2 if the percentages came from
someone who ate a lot of salty food?
chapter
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03
Table 3.3 shows the blood glucose levels of
two people after consuming 50 g of glucose
in a can of drink. Plot the data from the table
into a graph. Put time on the horizontal axis.
8 a Describe the changes that take place if the
amount of water in our body is significantly
reduced.
b How does this affect the functioning of the
body?
9 Name the two hormones that help control
glucose levels in the body. Explain why two
hormones are required, not just one.
10 Draw a flow diagram showing the sequence of
events that occur when the levels of glucose in
the blood are high; for example, after a meal.
11 Prepare a consequence map of the events that
took place in Mark Dorrity’s muscle cells which
led to the condition he suffered known as
rhabdomyolysis.
Responding to change
155
w
e
i
v
e
r
r
e
t
p
a
03 ch
Key terms
Key ideas
anorexia nervosa
antibodies
antidiuretic hormone
antigen
bulimia
carcinogen
diabetes
ectothermic
endothermic
glucagon
glycogen
goose bumps
homeostasis
host
immunity
insulin
line of defence
lymphatic system
lymphocytes
macronutrients
macrophages
non-infectious disease
over-nutrition
parasite
pathogen
phagocytes
under-nutrition
vaccinations
vasoconstriction
vasodilation
vector
1 Construct a concept map illustrating the relationships between: first
line of defence, second line of defence, last line of defence, phagocytes,
macrophages, lymphocytes, antibodies, the lymphatic system, antigen,
immunity, vaccinations.
2 You have been provided with the answers in the crossword.
Your challenge is to make up the clues.
1
V
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C
T
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2
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5
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8
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10
11
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Worksheet 3.4
Lines of Defence is a copy
of this worksheet for you
to complete.
Questions
1 Pus in a wound can be seen as a good sign.
What does the appearance of pus tell us?
2 A vector, in relation to disease, is:
A an organism that carries the disease
B usually a biting insect
C a fungus that affects the skin
D an organism that carries disease
3 Antibodies are:
A chemical compounds produced by fungi and
used to kill bacteria
B foreign protein that enters the bloodstream
C a reaction of the body to organ transplants
D chemical compounds produced by the body
to counter some antigens.
Responding to change
169
4 The greatest problem in combating viral disease is:
A the rate of mutation
B culturing the viruses
C identifying the viruses responsible
D the absence of any cure for viral infections.
5 What can we do to help maintain the health of
our kidneys?
6 Classify the following as prevention or cure:
a Placing an antiseptic ointment on a fresh cut.
b Having a vaccination against cholera before
going overseas.
c Taking antibiotics when you have a sore throat.
d Washing your hands after going to the toilet.
e Isolating in quarantine an exotic bird that has
been found in luggage by a customs official.
7 Name the vitamin or mineral (left column) that
is lacking in people suffering from each of the
diseases (right column) listed in the table.
iron
rickets
vitamin A
anaemia
iodine
night-blindness
vitamin C
goitre
vitamin D
scurvy
8 Work with a partner to draw up a set of guidelines
for the running of fun runs and marathons. Give
reasons for each guideline you set. Divide your
guidelines into two lists:
a Environmental conditions that must be met for
such an event to go ahead.
b Precautions that should be put in place to ensure
the well-being of participants.
9 Normal core body temperature in humans is about
37°C. This is the optimal temperature for enzymecontrolled chemical processes within cells to occur.
What do you expect happened to the chemical
reactions within Mark’s muscle cells when his body
temperature reached 42.8°C? Explain.
10 In Europe, measles was thought of as a mild childhood
disease. Research the effect of measles on the
Australian Aboriginal population when Europeans first
came to this country. Provide an explanation for what
happened. Parents today are a lot more concerned
about the effects of measles and an immunisation
has been developed. Explain why people are more
concerned about their children suffering from measles
now than they were in the past?
170
Responding to change
11 Research the reasons for the increased incidence of
diabetes in Australia. Then prepare a pamphlet for
students of your age (14–15 year olds) explaining
the reasons and suggesting actions they could take
to minimise the chances of developing the disease
in the future.
12 Design a pamphlet or a multimedia presentation
explaining why immunisation is important.
13 An organism that carries a parasite from host to
host is called a vector.
a Using library or Internet resources, find out the
vectors for sleeping sickness and malaria.
b Draw a diagram showing details of the life cycle
of the organisms that cause these two diseases.
14 An experiment was carried out to find out whether
heating cabbage affected the amount of vitamin C
in it. The cabbage was put in a saucepan, covered
with water and brought to the boil. Samples of the
cabbage were tested at 10 minute intervals to find
their vitamin C content. The following table shows
the results.
Time after
boiling (min)
Vitamin C
(mg/per 100 g)
0
50
10
20
30
40
50
60
70
75
80
50
50
50
50
50
50
30
5
0
a Plot these results onto a graph.
b What does the graph show? Suggest reasons
for this.
c What advice would you give to people
cooking cabbage?
15 Consider the following two statements about bacteria.
a All bacteria cause disease.
b Life on Earth depends on bacteria for survival.
Decide whether they are true statements or
false statements. Provide a justification for
your decisions.
review
18 a Research the roles that Louis Pasteur,
Joseph Lister, Edward Jenner and
Alexander Fleming played in the control
and prevention of disease.
b Prepare a poster or PowerPoint presentation
to be displayed in your school.
19 Some diseases that have been common in
the past are no longer a major problem. There
have been a number of discoveries that have
led to the reduced incidence of some diseases:
ÿ antiseptics
ÿ antibiotics
ÿ the importance of personal hygiene
ÿ immunisation
ÿ improved community health.
Gather information about one of these areas.
Compare the situation in the past with the
current situation. Identify any individuals
or groups that had a major impact on
developments. Suggest actions that you
think should be taken to improve the
situation in the future.
chapter
16 In 1912, before anyone knew about vitamins, a
scientist performed two experiments using two
groups of young rats.
First experiment
Group A: rats were fed highly purified carbohydrate,
fat, minerals and water. The food contained no
vitamins although scientists did not know this.
Group B: rats were fed the same diet, but with
a few drops of milk added. Group A rats stopped
growing and lost weight. Group B rats grew
steadily and gained weight.
Second experiment
The milk was removed from the diet of the Group B
rats and added to the diet of the Group A rats.
Group A gained weight and Group B rats stopped
growing and lost weight.
These results told the scientists two important
things about milk.
a What are these two things?
b Why was the second experiment necessary?
17 The following diagram shows the life cycle of
the beef tapeworm. Suggest an effective way
of controlling the spread of tapeworm.
INGUT
AHEADPOPSOUT
OFTHEBLADDER
HEADATTACHES
TOWALLOFGUT
INFECTEDMEAT
EATENBYHUMAN
(5-!.
PRIMARYHOST
#/7
INTERMEDIATEHOST
LARVAHATCHES
INCOWSGUT
SEGMENTSTOWARDS
THEBACKBECOME
FULLOFEGGS
SEGMENTS
LOADEDWITH
EGGSPASSOUT
WITHFAECES
EGGSEATEN
BYCOW
LARVABORES
INTOABLOOD
VESSEL
LARVAFORMSBLADDER
INCOWSMUSCLES
Responding to change
171