Homeostasis

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  • Created by: Hindleyc
  • Created on: 11-04-19 20:08
What is homeostasis
Maintenance of an organisms internal environment with narrow set limits
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define
Maintenance of a constant internal environment in organisms
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What does it involve
maintaining the chemical make-up volume and other features of blood and tissue fluid within restricted limits
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What does it ensure
that the cells of the body are in an environment that meets their needs and allows them to function normally despite external changes
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what doesn't this mean
their are no changes
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What is there
continuous fluctuations
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What is it brought about by
Variations in the internal and external conditions such as changes in temperature Ph and water potential
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What do these changes occur around
a set point because Homeostasis is the ability to return to that set point and so maintain organisms in balanced equilibrium
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What are the 3 main features
Temperature, Blood sugar, Water
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Temp options
32,37,42
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how
thermoreceptors in skin before brain
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Blood sugar
80-100 mg glucose per 100ml of blood
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Water effects,
plant cell plasmolyses, animal cell crenates
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what is Blood temp and concentration controlled by
homeostasis
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What for
enzymes
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What is the internal conditions regulated by
the endocrine (hormones) nervous system and behavioural patterns
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How do organisms increase their survival chances
By modifying their internal environment in response to external environment
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Why is it important
Enzyme controlled reactions and maintaining water potential
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What are the enzymes that control the biochemical reactions within cells and other proteins such as channel proteins sensitive to
Changes in Ph and temperature (enzyme activity)
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what does Any changes to these factors do
reduce efficiency of enzymes or may even prevent them working altogether eg by denaturing them
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what can even small fluctuations in temp or ph do
impair the ability of enzymes to carry out their roles efficiently
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what does maintaining a constant internal environment mean
that reactions take place at a constant and predictable rate
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What do changes in WP affect
Cell size animal cell swell burst crenate
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What may changes to WP of the blood and TF cause
Cells to shrink and expand (even to bursting point) as a result of water leaving or entering by osmosis
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In both instances what can't the cells do
Operate normally
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What is essential is ensuring a constant water potential
maintenance of a constant blood glucose conc
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What does a constant blood glucose conc also ensure
reliable source of glucose for respiration in cells
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What are organisms with the ability to maintain a constant internal E
more independent of the external E (animals)
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why
can maintain a constant level of activity regardless of their environment (independence from external conditions)
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So what do they both have
a wider geographical range and therefore have a greater chance of finding food shelter etc
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What does the control of any self regulating system involve
series of stages that feature set point, receptor, controller, effector and feedback loop
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What is the set point
Desired level or normal at which the system operates
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What is this monitored by
Receptor which detects any deviation from the set point
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What does it inform
controller which co-ordiantes information from various receptors and sends instructions to an appropriate effector
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What does the Effector do
brings about the changes needed to return the system to the set points
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What does this return to normality create
feedback loop which informs the receptor of changes to the system brought about by the effector
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What does a system normally have
many receptors and effectors
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What is it important to ensure
that the information provided by receptors is analysed by the control centre before action is taken
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What does receiving information from a number of sources allow
a better degree of control eg temp receptors in skin signal skin cold and body temp should be raised
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What if info from the temperature centre in the brain indicates blood temp already above normal
sweating cools skin- situation could arise during strenuous exercise
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What is negative feedback
Self regulating mechanism
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When an effector has corrected any alteration in the set point what does this info need to be
relayed back to the receptor
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If it is not fed back what will happen
then the receptor will continue to stimulate the effector leading to an over-correction of the initial alteration
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When does this occur
When the feedback causes the corrective measures to be turned off
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so
it returns a system to its original level
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eg
temperature regulation
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If temp of blood increases
Thermoreceptors in hypothalamus send impulses to heat loss centre of the hypothalamus which in turn sends impulses to the skin resulting in vasodilation, sweating and lowering of body hairs
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If the fact that the blood temp has bene returned to normal is not fed back to the hypothalamus then what will happen
it will continue to stimulate the skin to lose body heat that could ultimately result in hypothermia
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What actually happens
now cool blood passes through the hypothalamus and thermoreceptors detect that blood is now lower
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so
cease to send impulses to the skin
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So what will stop
vasodilation sweating etc
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so
blood temp will remain at the appropriate level
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what has blood done and what is this
turned off the effector- negative feedback
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How does it work
There is a deviation from a set point (stress) then corrective action to return towards set point but overshoots to corrective action again etc
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what is set point
optimal conditions
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What does the stress or disturbance do
changes the internal environment
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What is change detected by
Receptors
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What is activated
Corrective measures
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What do corrective measures do
counteract the change back towards set point
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When are corrective measures initiated
whenever the internal environment deviates from its normal or acceptable level
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What is thermoregulation
example of -ve feedback loop
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What happens
direction of feature puts corrective mechanisms to bring down the feature but goes too low- doesn't stop instantly too low
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What are there when value of feature is too high or too low
Corrective procedures (mechanism)
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What happens tho
never get to exact value- above and below it
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Signal type, speed and duration of nervous control
Electrical (action potential), fast target cell in milliseconds, short lasting
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Signal type, speed and duration of endocrine control
Chemical (hormone), slow as blood stream, long lasting
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What is positive feedback
deviation from normal conditions is amplified leading to further deviation
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When does it occur
when the feedback causes the corrective measures to remain turned on
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In doing so what does it cause the system to
deviate even more from the normal level but examples are rare
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eg
Na+, breakdown of control systems (Read) body temp dec or oxytocin contractions after born (Childbirth) contractions stop
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Why is it rare
Produces harmful unstable conditions (not back to normal)
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If set point levels dec +ve feedback means
further decrease
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if set point levels increase +ve feedback
further increase
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Card 2

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define

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Maintenance of a constant internal environment in organisms

Card 3

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What does it involve

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Card 4

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What does it ensure

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Card 5

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what doesn't this mean

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