Transcript Regulation - SchoolRack

Regulation
Homeostasis
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Homeostasis
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“steady state”
Keeping constant (or close to it!) conditions in an
organism’s internal environment, even when the
external environment changes
37C body temperature, 7.4pH of blood
The interstitial fluid (ISF), which fills the
spaces between our cells, is primarily
responsible for maintaining homeostasis
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Why?
Homeostatic Control Systems
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Every homeostatic control system has 3
major components:
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1. Receptor
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2. Control Center
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Detects a change in some variable of the animal’s
internal environment
Processes information it receives from the receptor
and directs an appropriate response by the effector
3. Effector
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Performs the appropriate response, as dictated by the
control center
Homeostatic Control Systems
CONTROL CENTER
EFFECTOR
RECEPTOR
CHANGE HAPPENS
Negative Feedback
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Overall Idea:
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Change happens
Then, the response (by the EFFECTOR) is in the
OPPOSITE direction of the original change
Most common feedback system in animals
Often HORMONES or NERVES are the
messengers (receptors and effectors)
Negative Feedback
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Thermostat Example:
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Thermostat is set at 70˚
Temperature DROPS to
67˚
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Thermostat “tells” heater
to turn on to RAISE
temperature back to 70˚
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OPPOSITE
DIRECTIONS
 Checks and balances!
Negative Feedback Examples
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Blood Glucose Levels
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If blood sugar level is too LOW, glucagon
(hormone) tells liver to release glycogen (stored
sugar)
If blood sugar level is too HIGH, insulin (hormone)
tells liver to take glucose out of the blood and
store it in the liver as glycogen
Blood Sugar Regulation
Negative Feedback Examples
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Blood Calcium Levels
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If the blood calcium level is too LOW, parathyroid
hormone (made in parathyroid glands) causes
calcium to be released into the blood (from the
bones)
If the blood calcium level is too HIGH, calcitonin
(made in the thyroid gland) will cause calcium to
be absorbed from the blood (into the bones)
Negative Feedback Examples
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Body Temperature
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If the body temperature
gets too LOW, the
hypothalamus (a gland in
the brain – the “master
gland”) tells the body to
SHIVER to generate heat
If the body temperature
gets too HIGH, the
hypothalamus tells the
body to release heat as
sweat
Positive Feedback
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Overall Idea:
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Change happens
Then, the response is in the SAME direction as
the original change
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The change is AMPLIFIED, not reversed
Positive Feedback Examples
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Childbirth
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Oxytocin (hormone) is released, causing the
cervix to dilate and starting contractions
The dilation of the cervix and the contractions
cause MORE oxytocin to be released, therefore
intensifying the contractions
Positive Feedback Examples
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Blood Clotting
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Platelets accumulate at the site of a blood vessel
break or tear
This causes MORE platelets to come, therefore
causing blood to clot
Also causes fibrin (inactive) to be converted to
fibrinogen (active)
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Signal Transduction Pathway 
Thermoregulation
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Endotherms
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“warm-blooded”
Maintain a stable internal body temperature
Not as affected by external changes
Ectotherms
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“cold-blooded”
Body temperature fluctuates with the external
environment
Very affected by external changes
AP Lab 10 Connection…
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Daphnia
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Taxonomy?
Expose Daphnia to
increasingly-warm
temperatures
What is the relationship
between metabolism
(think enzyme reactions!)
and heart rate?
 What should happen?
 Why?