Unit 2: The Continuation of Life

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Unit 2 The Continuation of Life
Higher Human Biology

• Chapter 24
• Regulating Mechanisms

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• Learning Intentions

• Success Criteria

• To know how the heart rate is regulated.

• Outline the principle of negative feedback
• Explain how heart rate is controlled with
  reference to the role of hormonal and nervous
  system

3
Human Internal Environment
A humans internal environment is the millions of
body cells and the tissue fluid that bathes
them. For a healthy body, all body parts must
work together keeping the internal environment
within tolerable limits. e.g. Human body must be
maintained at 37C to provide optimum conditions
for enzyme controlled reactions The features of
the internal environment are controlled by
homeostasis.
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Homeostasis
HOMEOSTASIS is the maintenance of the bodys
internal environment within certain tolerable
limits despite changes in the bodys external
environment (or changes in the bodys rate of
activity).
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The value of Homeostasis
Homeostasis is of survival value because it
maintains the bodys internal environment at a
relatively steady optimum state. If the body is
exposed to extremely adverse conditions (e.g.
freezing temperatures or absolutely no water)
homeostasis will eventually break down, which in
extreme cases can be fatal.
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8. Negative Feedback Control
When a factor affecting the bodys internal
environment deviates from its norm (or set-point)
the body responds to correct the change.
Image source www.hw.ac.uk
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8. Negative Feedback Control Receptors detect
change and send messages to effectors.

• The change in the factor is detected by
  receptors.
• These send out nerve or hormonal messages which
  are received by effectors.
• The effectors then bring about certain responses
  which counteract the original deviation from the
  norm and return it to a set point.

Image source www.hw.ac.uk

• This corrective homeostatic mechanism is called
  NEGATIVE FEEDBACK CONTROL.
• It provides the stable environmental conditions
  needed by the bodys community of living cells to
  function efficiently and survive.

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9. Control of Heart Rate Pacemaker
Although the heartbeat is initiated by the
pacemaker tissue also known as a Sino-atrial node
(SAN). However, heart rate is not set at a fixed
pace. Heart rate can be altered by nervous and
hormonal activity both of which exert control
over rate (though not initiation) of heartbeat.
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The Nervous System
The nervous system is a network of specialised
cells that communicate information about an
individuals surroundings and itself. It
processes this information and causes reactions
in other parts of the body.

Image source www.drstandley.com
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Control of Heart rate. The Autonomic Nervous
System

• The autonomic nervous system (ANS) controls
  involuntary responses to stimuli by the body.
• Autonomic nerves serve
• heart muscle
• smooth muscle
• Glands
• all internal organs.
• The ANS acts on these various effectors to
  maintain
• homeostasis within the body (parasympathetic
  branch)
• response to stress the "fight or flight"
  response (sympathetic branch)

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Parasympathetic v Sympathetic
homeostasis
response to stress
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The Autonomic Nervous System The Vagus Nerve

• The vagus nerve is the longest nerve in the body,
  and one of the most important. It sends commands
  to, and takes information from many important
  organs including the heart and lungs.

People have two vagus nerves, one for each side,
running roughly parallel from the medulla in the
brain to the bowels.
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• Control of Heart Rate
• Autonomic nervous control

The heart is part of the autonomic nervous
system. It has branches of 2 parts of the
autonomic nervous system. These 2 pathways have
opposite effects on heart rate (are
antagonistic).
Heart rate is regulated by control centres within
the medulla of the brain.
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• Control of Heart Rate
• Autonomic nervous control

The sympathetic cardiac nerves carry nerve
impulses from the cardio-accelerator centre of
the brain to the heart.
The cardio-inhibitor centre sends nerve impulses
via the parasympathetic vagus nerve.
Image source http//courses.scholar.hw.ac.uk
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Two antagonistic pathways

• The sympathetic and parasympathetic pathways are
  antagonistic to one another. i.e. They have an
  opposite effect on heart rate.
• An increase in the number of nerve impulses
  conducted to the to the pacemaker by the
  sympathetic nerve causes an increase in heart
  rate.
• An increase in the number of nerve impulses
  conducted to the to the pacemaker by the
  parasympathetic nerve causes a decrease in heart
  rate.

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B. Control of Heart Rate Hormonal Control
The adrenal glands produce the hormone
adrenaline, which also affects heart rate.
During exercise or stress.
Sympathetic nervous system causes the adrenal
glands to release adrenaline
At pacemaker adrenaline causes an increase in
the rate of cardiac impulses
Increase in heart rate
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• Learning Intentions

• Success Criteria

• To know how the heart rate is regulated and the
  effects of exercise on the cardiovascular and
  respiratory systems.

• Analyse graphs showing distribution of blood to
  tissues at rest and during exercise
• Calculate cardiac output under different
  conditions

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Control of the Heart. C. Exercise

• Vigorous exercise can cause huge changes of the
  bodys internal environment.
• The metabolic rate increases in the muscles that
  are working hard.
• need more oxygen
• need more glucose
• produce more CO2.
• The body adjusts to meet these demands
  and returns to normal a.s.a.p

Breathing rate depth increases to increase
ventilation this promotes O2 uptake and CO2
removal
View the Scholar animation http//courses.scholar
.hw.ac.uk/vle/scholar/session.controller?actionvi
ewContentcontentGUID92be7024-6e80-a2da-455b-e306
b499a29a
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Carbon dioxide as the stimulus
Experiments show (see Torrance p188) high levels
of CO2 acts as the stimulus to trigger an
increase in breathing rate. The graph below
shows the results!
Only the abnormal air type 2 is found to cause
breathing rate to increase sharply. It is
concluded that it is the high level of CO2 in the
abnormal air that acts as a stimulus triggering
increased rate of breathing.
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Carbon dioxide as the stimulus, Cont

• Further experiments show
• Depth of breathing also increases in response to
  inhalation of air rich in CO2. ,
• In a person under going strenuous exercise it is
  the increased level of CO2 in the bloodstream
  that acts as the main stimulus for bringing about
  an increase in rate and depth of breathing.

Oxygen as a stimulus

• It is worth noting that experiments also show
  that severe lack of oxygen will eventually also
  cause an increased rate and depth of breathing.

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The effect of Exercise on the Respiratory System
Homeostatic control Part 1

• Chemoreceptor's in the carotid arteries and aorta
  are sensitive to the concentrations of CO2 in the
  bloodstream. A rise in CO2 levels during vigorous
  exercise causes these sensory cells to send an
  increased number of nerve impulses to the
  respiratory control centre in the medulla.

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The effect of Exercise on the Respiratory System
Homeostatic control Part 2!

• This region of the brain responds by sending a
  greater number of nerve impulses to the
  intercostal muscles and diaphragm. The subsequent
  increased activity of these structures brings
  about an increase in rate and depth of breathing.
• Excess CO2 is removed and the internal
  environment is kept within tolerable limits.

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SUMMARY The effect of Exercise on the
Respiratory System Homeostatic control
More nerve impulses sent to respiratory control
centre in medulla
Chemoreceptors in cartoid arteries aorta detect
CO2 concentration
More nerve impulses sent to intercostal muscles
and diaphragm
An example of negative feedback control
Breathing rate depth increases causing a return
to normal CO2 concentration
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B. Effect of exercise on cardiovascular system
Heart rate (pulse) number of cardiac cycles per
min
Stroke volume volume of blood expelled by each
ventricle on contraction
Cardiac output volume of blood pumped out of a
ventricle per min
All of these increase with exercise and even more
with strenuous exercise
The stronger the contraction the higher the
stroke volume
Cardiac output
Heart rate
Stroke volume

X
To convert ml to litres
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Task!!!
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Try this calculation! These figures actually show
the effect of exercise on cardiac output for the
average adult human!
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Effect of exercise on cardiovascular system

• The cardio-accelerator centre in the medulla
  sends impulses via the sympathetic nerves in the
  heart making it beat more often and powerfully.
• This increase in both heart rate and stroke
  volume brings about the increase the total
  cardiac input needed to boost delivery of
  oxygenated blood to respiring tissues and to
  return deoxygenated blood to the lungs.
• During very strenuous exercise, the cardiac
  output of an average person can increase by X5.
  This is mainly due to the increased heart rate.

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Control of local distribution of blood

• All parts of the body require an adequate supply
  of blood to function efficiently. But the
  demands by each part are not constant.
• At rest the vegetative functions (digestion,
  urine production etc.) are promoted.
• When the body undergoes strenuous activity
  much blood is diverted to the skeletal muscles
  (for extra O2 and glucose).

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Control of local distribution of blood
During exercise
Chemoreceptors detect CO2 concentration
Nerve impulses sent to cardio-accelerator centre
in medulla
Nerve impulses sent to arterioles in abdominal
organs cause muscles in arteriole wall to
contract to restrict blood flow
Nerve impulses sent to arterioles in working
muscles causing arteriole wall to relax to
increase blood flow
An example of negative feedback control
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Distribution of blood to tissues during exercise
During exercise blood flow to various parts of
the body changes.
Tissue Change due to exercise Reason
Heart Increase to meet its demand for more glucose and oxygen
Brain None Basic energy demands of cells not affected
Kidneys Decrease kidney processes can be postponed until the exercise is finished
Skin Increase allow the heat produced in muscles to be radiated from the surface of the skin
Intestines liver Decrease processes of digestion and absorption can be postponed until the exercise is finished
Skeletal muscles Increase to meet their demands for more glucose and oxygen
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Task Torrance-TYK pg192 Qu 1-3
32

• Learning Intentions

• Success Criteria

• To know how the heart rate is regulated and the
  effects of exercise on the cardiovascular and
  respiratory systems.
• To know how blood sugar levels and body
  temperature are regulated.
• .

• Explain how blood sugar level is controlled by
  the hormones insulin, glucagon and adrenalin.
• Analyse glucose tolerance curves of normal and
  diabetic subjects

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Regulation of Blood Glucose Concentration
Blood sugar level must be kept within a certain
range to provide the energy needed by cells for

• Synthesis of DNA, proteins and other complex
  molecules.
• Active uptake of ions.
• Muscle contraction.

Cells are therefore constantly using up the blood
sugar.
To ensure a regular supply regardless of food
consumed the body uses homeostasis!
Image source library.tedankara.k12.tr
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Liver as a storehouse

• About 100g of glucose is stored as GLYCOGEN in
  the liver. Glucose can be added or removed from
  this reservoir if stored carbohydrate depending
  on supply and demand.

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Control of blood sugar Insulin and glucagon

• Insulin and glucagon are two hormones that
  control how much glucose (sugar) is in the blood
• These hormones are made in the pancreas.
• Your pancreas contains small groups of cells
  called the islets (or islands) of Langerhans.

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Pancreas

• When you eat a meal, the amount of sugar in your
  blood rises. The cells in your pancreas react by
  making more insulin.
• When your blood sugar levels are low, the cells
  in your pancreas react by making more glucagon.

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What does insulin do?

• After digestion, glucose enters your bloodstream.
• The Islets of Langerhans in the pancreas detects
  an increase in blood sugar level.
• These cells produce the hormone insulin, which is
  then transported to the liver in the bloodstream.
• Insulin activates an enzyme to catalyse the
  reaction
• glucose
  glycogen
• This decreases the blood sugar level.
• Glycogen, a long chain carbohydrate, is stored in
  the liver until it is needed e.g. when you are
  sleeping

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What does glucagon do?

• Glucagon stops your blood glucose level from
  dropping too low.
• When you exercise, your body uses the glucose in
  your blood to power your muscles. Your pancreas
  senses that you're using up your glucose supply.
• As your blood glucose level drops, your pancreas
  stops making insulin and your pancreas makes
  glucagon
• Glucagon activates an enzyme in your liver which
  catalyses the following reaction
• Glycogen
  Glucose
• These activities push up the amount of glucose in
  your blood.

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Control of blood sugar
40
Task, can you place the boxes into the
appropriate places in the table below!
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Watch this
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Adrenaline Stress Response
The adrenal glands produce the hormone adrenaline
in an emergency when the body needs a quick
supply of glucose (for fight or
flight) Adrenaline is secreted by the adrenal
gland and inhibits the secretion of insulin and
promotes the breakdown of glycogen to glucose,
overriding the normal homeostatic control.
When the crisis is over the normal homeostatic
control then returns the blood sugar level to
its norm.
Image source www.rch.org.au
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Alternative Homeostasis
All factors controlled by homeostasis can be
represented by a standard diagram.
When a factor deviates from the norm and is
returned to normal it often overshoots the mark,
which triggers the reverse set of corrective
mechanisms.
So factors in a state of dynamic equilibrium are
constantly wavering on either side of the norm.
This is usually represented by 2 linked circuits.
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Diabetes
Diabetics suffering from Diabetes mellitus can
not produce enough (if any) insulin which causes
their blood sugar level to get too high. Because
of this the kidneys can not reabsorb all of the
glucose from the glomerular filtrate and so
glucose is excreted in the urine.
Diabetes used to be fatal but can now be treated
with a carefully controlled diet or insulin
injections.
Image source
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Glucose Tolerance Test
Glucose tolerance is the capacity of the blood to
deal with the glucose we eat. It depends on the
bodys ability to produce enough insulin.
A known mass of glucose is drunk. Then the level
of glucose in the blood is monitored graphed to
give a glucose tolerance curve.
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Glucose Tolerance Curves
Glucose level remains high
Severe diabetic insulin injections and
carefully controlled diet needed
Mild diabetic condition controlled by diet
Delayed response
Glucose level returns to normal quickly
Not diabetic - Insulin production normal
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Watch this!!!
http//www.bbc.co.uk/learningzone/clips/the-effect
-of-high-sugar-intake-on-blood-sugar-levels/5371.h
tml
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• Learning Intentions

• Success Criteria

• To know how the heart rate is regulated and the
  effects of exercise on the cardiovascular and
  respiratory systems.
• To know how blood sugar levels and body
  temperature are regulated.

• Explain how temperature is controlled with
  reference to
• The role of the hypothalamus
• Nerve communication between the hypothalamus and
  effectors
• Involuntary and voluntary responses
• Changes in ability to control body temperature
  with age

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Control of Body Temperature

• Core body temperature must remain at 37oC
• Careful control of the blood supply to the skin
  can do this by reducing blood flow to the colder
  extremities in cool conditions.

50
Regulation of Body Temperature

• Another example of homeostasis is the bodys
  regulation of body temperature.
• The hypothalamus (the bodys temp-monitoring
  centre)monitors body temperature in two ways

1. It contains central thermoreceptors which are
   sensitive to temperature changes in the blood,
   allowing detection of the bodys core
   temperature.
2. It acts as a thermostat by detecting nerve
   impulses from thermoreceptors in the skin (this
   conveys info about the surface temp of the body).

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Regulation of Body Temperature
The hypothalamus sends nerve impulses to the
effectors allowing the body to correct
overcooling or overheating by

1. Production of sweat.
2. Control of body hairs.
3. Vasodilation or Vasoconstriction of blood flow in
   the skin

Image source www.pg.com
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Role of the Skin
The skin plays a leading role in temperature
regulation. In response to nerve impulses from
the hypothalamus the skin can act as both a
receptor and an effector.
Image source images.encarta.msn.com
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Role of the Skin

• The skin helps to correct overheating of the
  body by
• Increasing the rate of sweating.
• Vasodilation

• The skin help to correct overcooling of the body
  by
• Decreasing the sweat of sweating.
• Vasoconstriction
• Contraction of erector muscles

54
Correcting and heat loss and gain 1 3 .
Sweating - Why sweat?
Sweat glands dampen the skin. This loses heat by
causing evaporation of the sweat
1. When we sweat, heat energy from the body
causes water from sweat to evaporate which cools
the body.
3. When we are cold sweating in inhibited to
conserve heat.
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Sweating under pressure!
Sweating caused by heat
Sweating caused by muscular contraction
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FYI Nine Sweaty Facts

• Humans are the most prolific sweaters in the
  entire animal kingdom
• Sweating is accomplished through specialized
  sweat glands
• These glands are found in the dermis and
  epidermis, distributed all over the body, except
  for the margins of the limbs, sex organs, and ear
  drums
• They average between 150 and 340 glands/cm2 of
  skin for a total of between 2,000,000 and
  5,000,000
• Add them all together and you get a hole the size
  of your mouth
• The sweat glands are innervated by the
  sympathetic nervous system
• When a rise in core temperature is detected by
  the hypothalamus, impulses to the sympathetic
  system cause an increase in sweat output
• The sweat gland consists of a deep coiled portion
  and a duct that opens on the skin
• The duct aids in the re-absorption of
  electrolytes, mainly sodium and chloride, in the
  sweat so that the fluid discharged onto the skin
  has had the electrolyte concentration reduced by
  a factor of about 20

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2. Correct overheating Vasodilatation
When we get too hot arterioles leading to the
skin become dilated, which allows lots of blood
to flow near the skins surface and a loss of heat
from the blood by radiation.
FYI Red skin indicates vasodilatation, Alcohol
increases this hence rosy cheeks after a few
tipples!
View the animation Scholar Unit 2, Figure 6.10
Vasodilation and vasoconstriction
http//courses.scholar.hw.ac.uk/vle/scholar/sessio
n.controller?actionviewContentbacksearchconten
tGUID8062401e-bfa9-4231-9508-4b6df971a8b6
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4. Correct overcooling Vasoconstriction
When we are cold arterioles leading to the skin
become constricted, which reduces the flow of
blood to the skins surface so only a little heat
is lost from the blood by radiation.
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5 Preventing overcooling Contraction of erector
muscles
In a cold environment we need to reduce heat
loss. This system is more efficient in furry
animals than in humans.
Nerve impulses from the hypothalamus cause the
erector muscles in our skin contract causing the
hair (or feathers in birds) to rise up. This
increases the layer of insulating air trapped by
them so keeps the body warm.
hairs erect
erector muscles relaxed
erector muscles contracted
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hair
Surface of skin
Hair muscle
Contraction of this muscle makes the hair stand
on end, trapping more insulating air.
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Summary Body Temperature
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Activity Complete the table using the given terms
63
ANSWERS
64
Quick Quiz
65
Answers
66
Investigating response to sudden heat loss
If one hand is plunged into icy water the
temperature of that hand will drop, as will the
temperature of the other hand (this is measured
with a device called a THERMISTOR this can take a
measurement every 30 seconds) . It is therefore
concluded when heat is lost from one extremity,
there is a compensatory reduction in temperature
that occurs in the matching extremity.
This helps to conserve the temperature of the
bodys core so that the bodys core temperature
will stay the same. Extremities vary in
temperature much more than the bodys core.
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Role of other effectors in temperature regulation
These other effectors help temperature regulation
by generating heat when it is needed
Shivering by skeletal muscles muscle
contractions which generate heat energy, helping
return temperature to normal
Liver high metabolic activity produces heat and
helps to maintain body temperature

• Hormones increase metabolic rate
• release of adrenaline during sudden exposure to
  cold temperatures
• release of thyroxin

68
Voluntary Responses for temperature regulation.
Temperature regulation mechanisms controlled by
the hypothalamus are subconscious and
involuntary.
However body temperature is also controlled by
voluntary responses e.g.
When body temperature drops (or rises) nerve
impulses pass the information to the thinking
part of the brain (the cerebrum), which makes the
person feel cold (or hot) and react.
69
Coping with heat and cold

• Factors Affecting Thermal Acclimation
• Age
• Both infants and elderly have lessened ability to
  acclimatize to heat or cold
• Body size and shape
• The surface area to weight ratio will affect the
  level of acclimatization attainable
• Body composition
• Subcutaneous adipose deposits (fat) insulate the
  core and make it more difficult to dissipate heat
  in hot or easier to retain heat in the cold

70
Involuntary responses

• The mechanisms of temperature regulation
  discussed thus far have all been involuntary
  responses, which are controlled at a subconscious
  level by the hypothalamus.

71
Voluntary Responses
However body temperature is also controlled by
voluntary responses e.g.
When body temperature drops (or rises) nerve
impulses pass the information to the thinking
part of the brain (the cerebrum), which makes the
person feel cold (or hot) and react.
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Watch this
73

• Learning Intentions

• Success Criteria

• To know how body temperature is regulated.

• Discuss Hypothermia in infancy old age

74
Temperature regulation in infants

• The exposed area of a small animal relative to
  its volume is greater than that of a larger
  animal of similar shape.
• So the relative surface area of a baby is greater
  than an adults. So a baby would suffer more heat
  loss than an adult.

• Babys involuntary responses to decrease in
  temperature
• vasoconstriction of skins blood vessels
• increase in metabolic rate in brown fat
  (adipose) tissue (more supplied with blood
  vessels than white fat)

Brown fat deposits are found in newborns and
hibernating mammals, and can produce heat to warm
the body.
75
Hypothermia
Hypothermia is caused when the bodys core
temperature drops to a dangerously low
temperature.
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Critical Temperature
The lower critical temperature is the external
temperature (27oC) when a naked adults body can
only just manage to maintain normal body
temperature.
Any temperature below this needs heat energy to
be generated by metabolism to keep the body at
37oC.
As babies have a larger surface area they are
more susceptible to the effects of cold
temperature and have a higher critical
temperature adults.
If a newborn baby is exposed to cold
temperatures, it will use up its limited food
reserves to keep the body warm and once these are
used up its core body temperature will drop.
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Hypothermia in Babies
Temperatures that are uncomfortably cold, but
tolerable, for adults can cause hypothermia or
even death in babies because their bodys
temperature regulation mechanisms are not fully
developed.
Pre-term (premature) babies are even more
susceptible to hypothermia because

• Their temperature regulation
• mechanisms are even less developed.
• Small size, so larger relative surface area to
  loose heat.
• Higher critical temperature burn food reserves
  at higher temperatures than normal.
• Small food reserves which run out quickly.

78
Hypothermia in the Elderly

• The elderly are more susceptible to hypothermia
  because
• Their temperature regulation mechanisms are less
  efficient
• Blood vessels fail to undergo vasoconstriction
  when exposed to cold temperatures
• Fail to shiver when cold

• They have a slower rate of metabolism so dont
  generate heat needed to keep body warm
• They are less active so dont generate heat
  through movement
• Body temperature drops when you sit for long
  periods in a cold room

79
Breakdown of homeostasis
Homeostasis only works in certain limits!!
If exposed to an extreme environmental condition
for a long time the negative feedback control
breaks down.
For example, the elderly often fail to realise
the signs of hypothermia so dont take corrective
action (e.g. turning up the heating). If their
homeostatic temperature control has broken down
their body cant recover on its own. They become
hypothermic and need urgent medical attention.
80
Task Torrance-TYK pg199 Qu 1-3
81
Task Torrance AYK pg199/202 Qus 1-6
82
Essay style Questions Scholar

• Give an account of hormonal control of the
  regulation of blood sugar levels.

83
ANSWER Give an account of hormonal control of
the regulation of blood sugar levels. (10)

• Each numbered point is worth 1 mark. The
  information in brackets is not a required part of
  the
• Correct facts (8 marks)
• Insulin is secreted by the pancreas/islets of
  Langerhans when blood glucose/sugar levels are
  high
• Insulin controls/causes the conversion of blood
  glucose/sugar into glycogen (not 'converts')
• Glycogen is stored in the liver
• When blood glucose/sugar levels return to normal,
  insulin production decreases
• Glucagon is secreted by the pancreas/islets of
  Langerhans when blood glucose/sugar levels are
  low
• Glucagon controls/causes the conversion of
  glycogen to glucose (not 'converts')
• When blood glucose/sugar levels return to normal,
  glucagon production decreases
• This type of control is known as negative
  feedback control (mark if given for either
  insulin or glucagon, but not both)
• In emergency situations, (the hormone) adrenaline
  is secreted by the adrenal glands
• Adrenaline overrides the action of insulin
• Once the emergency is over, adrenaline levels
  return to normal
• and the homeostatic control (by insulin and
  glucagon) is regained
• Coherence (1 mark)
• One mark is given if at least 5 relevant points
  provided.
• Relevance (1 mark)

84
SQA Past Paper 2012

• Qu 2b. Describe involuntary mechanisms of
  temperature control. (10).

85
SQA Past Paper 2008

• Give an account of temperature regulation in cold
  conditions under the
• following headings
• (i) voluntary responses (3)
• (ii) involuntary responses (5)
• (iii) hypothermia (2)