Transcript To be able to describe how the main homeostatic mechanisms

To be able to describe the general principles of
homeostasis .
To be able to explain how the main homeostatic
mechanisms work.
.
Homeostasis
Negative feedback
To maintain their internal environment organisms need a self regulating mechanism. In
most animals this is achieved by negative feedback.
Negative feedback works by initiating corrective mechanisms whenever the internal
environment deviates from its normal or acceptable level.
Thermoregulation: an example of a negative feedback loop
body temperature
increases
corrective
mechanisms
normal body
temperature
normal body
temperature
body temperature
decreases
corrective
mechanisms
Nervous
or
endocrine
control?
The nervous system and endocrine system are both involved in controlling the
internal conditions of a mammal.
nervous control
endocrine control
electrical
chemical
(action potential)
(hormones)
speed of signal
reach the target cells in
milliseconds
relatively slow, travelling in
the bloodstream
duration of signal
short lasting
long lasting
signal type
Behavioural
control
Kineses and taxes are simple behavioural mechanisms to maintain homeostasis. Both
involve the movement of organisms in response to external stimuli.
In a kinesis, the animal responds to the presence and intensity of the stimulus, but not its
position. For example, the drier the conditions, the faster a woodlouse moves, and the
fewer turns it makes. This simple behaviour tends to move woodlice towards damp areas.
In a taxis, the direction of the stimulus is
important. For example, woodlice move
directly away from light.
Temperature
Core temperature
• The core temperature of the human body
is 37°C
• The core of the human body includes the
organs of the thorax, abdomen and the
head
• This is where the vital organs are located
• Their enzyme systems must operate in
optimum conditions
• The periphery of the body can withstand
some deviation from the core temperature
Maintaining the body temperature
Keeping warm
Staying cool
Increased insulation,
subcutaneous fat reduces
the conduction of heat from
the body
Increase blood flow to skin,
increases conduction and
radiation of heat from the
body
Reduced sweating
decreases evaporation
Increased sweat secretion,
increases evaporation
Increased shivering,
increases heat produced by
muscle tissue 2 to 5 times
Reduced activity
© 2008 Paul Billiet ODWS
Core body
temperature
>37°C
Thermoreceptors
Hypothalamus
nerves
Muscles
reduce
activity
Sweat
glands
increase
secretion
Muscles of
skin arteriole
walls relax
Skin arteries dilate
More blood to the
skin.
More radiation &
conduction of heat
More water covers the
skin.
More evaporation
Less heat generated
NEGATIVE
FEEDBACK
Thermoreceptors
Core body
temperature
>37°C
Thermoreceptors
Blood
temperature
Muscles of
skin
arteriole
walls relax
nerves
Hypothalamus
Sweat
glands
increase
secretion
Muscles
reduce
activity
Body
loses
heat
Return
to 37°C
NEGATIVE
FEEDBACK
Thermoreceptors
Blood
temperature
Muscles of
skin
arteriole
walls
constrict
nerves
Core body
temperature
<37°C
Thermoreceptors
Sweat
glands
decrease
secretion
Hypothalamus
nerves
Muscles
shivering
Body
loses
less
heat
Return
to 37°C
Body
gains
heat
Use this diagram to produce a feedback loop showing how the body responds
When the core body temperature drops.
Glucose
Water levels
ADH – too little water in blood
ADH – too much water in blood
Also
•
•
•
•
Blood pH
Electrolytes ( salts)
Blood pressure
Conditions within the digestive system
Task
• Explain the general principles of homeostasis
using the control of blood glucose as an
example of negative feedback (750 words)