Transcript temperature regulation

How does varying temperature affect
the speed of woodlice?
Sarah, Eliza and Lydia
Temp (oC)
Distance
travelled
(cm)
Time taken
(s)
0
10
16
20
10
5
40
10
Pip, Jack and Lewis
23
Temp (oC)
Distance
travelled
(cm)
Time taken
(s)
0
10
17
20
10
12
40
10
8
Speed (m/s)
Speed (m/s)
Calculate the speed for each set of results. (2)
Describe and suggest reasons to the trends with
each set of results (5)
Temperature Regulation
By the end of the lesson you will be able
to:
(d) define the terms negative feedback, positive
feedback and homeostasis;
(e) explain the principles of homeostasis in
terms of receptors, effectors and negative
feedback;
(f) describe the physiological and behavioural
responses that maintain a constant core body
temperature in ectotherms and endotherms,
with reference to peripheral temperature
receptors, the hypothalamus and effectors in
skin and muscles.
Feedback Mechanisms
Feedback Mechanisms  examples
negative feedback,
(in physiology) a decrease in function in
response to a stimulus. For example, the
secretion of follicle-stimulating hormone
decreases as the amount of circulating
oestrogen increases.
positive feedback,
(in physiology) an increase in function in
response to a stimulus. For example,
micturition increases after the flow of urine has
started, and the uterus contracts more
frequently and with greater strength after it has
begun to contract in labour.
Positive Feedback Mechanisms
Homeostatic systems utilising positive feedback exhibit two primary
characteristics:
1. Time limitation – Processes in the body that must be completed within a
constrained time frame are usually modified by positive feedback.
2. Intensification of stress – During a positive feedback process, the initial
imbalance or stress is intensified rather than reduced as it is in negative
feedback.
Typical Positive Feedback Process
Stress
Intensifies
Sensor
Control Center
Effector
Homeostatic Regulation of Child Birth through
Positive Feedback
Pressure of Fetus on
the Uterine Wall
Nerve endings in the uterine
wall carry afferent messages
to the Hypothalamus
Intensifies
Increasing strength of
uterine contractions
Production and Release
of Oxytocin into the
Blood
The birth of the child will bring this process to a close. Other
examples of positive feedback regulation occur during milk
letdown and blood clotting.
Glossary
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Maintain – keep up.
Constant – the same.
Internal – inside the body.
Environment – surroundings of the body.
What is Homeostasis?

Body cells work best if they have the correct
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Temperature
Water levels
Glucose concentration
Your body has mechanisms to keep the cells
in a constant environment.
What is Homeostasis?
The maintenance of
a constant
environment in the
body is called
Homeostasis
Controlling body temperature
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All mammals maintain a constant body
temperature.
Human beings have a body temperature of
about 37ºC.
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E.g. If your body is in a hot environment your
body temperature is 37ºC
If your body is in a cold environment your body
temperature is still 37ºC
The Transfer of thermal energy
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Controlling body temperature
Animals with a large surface area compared to
their volume will lose heat faster than animals
with a small surface area.
Volume = _______
Volume = _______
Surface area = ______
Surface area = ______
Volume : Surface area
ratio = ___________
Volume : Surface area
ratio = ___________
Controlling body temperature
Volume : Surface
area ratio = 1:6
For every 1 unit
of heat made,
heat is lost out
of 6 sides
Volume : Surface
area ratio = 1:5
For every 1 unit
of heat made,
heat is lost out
of 5 sides
Controlling body temperature
Volume : Surface
area ratio = 1:6
Volume : Surface
area ratio = 1:5
The bigger the
Volume : Surface Area ratio
is, the faster heat will be lost.
Penguins huddling to keep warm
Why do we need to regulate:
Internal body temperature
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To provide the optimum conditions for
enzyme-catalysed reactions to be
carried out.
Body Temperature
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Normal internal body temperature
is 370C.
Temperatures above this:
denature enzymes and block
metabolic pathways
Temperatures below this:
slow down metabolism and affect
the brain.
Water Bath
Temperature set on thermostat
Too cool? Heater kicks on and temperature goes up
Too warm? Heater stays off until bath cools down
Constant checking and turning on and off
Control of homeostasis
through feedback
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Feedback system- cycle of events in which the
status of a body condition is continually
monitored, evaluated, changed, re-monitored,
re-evaluated, etc.
3 basic components of a feedback system
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1) receptor
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2) control centre
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sensor that responds to changes (stimuli)
sets range of values, evaluates input and sends
output
3) effector
–
receives output from control centre and
produces a response
Body Temperature Control
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The hypothalamus
acts as a thermostat
and receives nerve
impulses from heat
and cold
thermoreceptors in
the skin.
There are also
receptors in the
hypothalamus- called
central
thermoreceptors.
These detect changes in
blood temperature.
Vasoconstriction and
Vasodilatation
Correction of overheating
1.
2.
3.
Detected by thermoreceptors in the
hypothalamus.
Causes vasodilation.
Sweating
Cooling down
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When it's hot and you
need to cool down,
muscles at each hair
relax.
Hairs lie close to the
skin.
Air does not act as an
insulating layer.
Sweating
How does it work?
Heat energy in the
body is used to
convert the water
in sweat to vapour
cooling down the
body.
What mechanisms are there to
cool the body down?
1.
Sweating

When your body is hot, sweat glands are
stimulated to release sweat.
The liquid sweat turns into a gas (it
evaporates)
To do this, it needs heat.
It gets that heat from your skin.
As your skin loses heat, it cools down.
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Sweating
The
skin
What mechanisms are there to
cool the body down?
2.
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Vasodilation
Your blood carries most of the heat energy
around your body.
There are capillaries underneath your skin
that can be filled with blood if you get too
hot.
This brings the blood closer to the surface
of the skin so more heat can be lost.
 This is why you look red when you are
hot!
This means more heat is lost from the surface of the skin
If the temperature
rises, the blood
vessel dilates (gets
bigger).
Correction of overcooling
1.
2.
3.
4.
Detected by thermoreceptors in the
hypothalamus.
Causes vasoconstriction.
Decreased sweating
Shivering
Keeping warm
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When it's cold, the
muscle contracts
pulls the hair up.
A layer of warm air
accumulates around
the hair and
insulates the
organism.
Heat retained
Shivering
How does it
work?
What mechanisms are there to
warm the body up?
1.
Vasoconstriction

This is the opposite of vasodilation
The capillaries underneath your skin get
constricted (shut off).
This takes the blood away from the
surface of the skin so less heat can be
lost.
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This means less heat is lost from the surface of the skin
If the temperature
falls, the blood
vessel constricts
(gets shut off).
What mechanisms are there to
warm the body up?
2.
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Piloerection
This is when the hairs on your skin “stand up”
.
It is sometimes called “goose bumps” or
“chicken skin” if you are a bit weird like
Americans!
The hairs trap a layer of air next to the skin
which is then warmed by the body heat
The air becomes an insulating layer.
Voluntary responses
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In humans the cerebrum “makes”
people feel cold or hot.
They can then e.g. put on more
clothes, eat a hot meal, exercise etc
as appropriate.