Life = “Steady State”Food
Water
O2
Heat
Feces
Urine
CO2
Heat
Constancy of Internal Environment:
HOMEOSTASIS“Delicate Balance” = Regulation
Temperature It’s good to be constant
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Bod
y te
mpe
ratu
re (
ºC)
Environmental temperature (ºC)
Homeothermconstant body temp
Heterothermbody temp varies with environment
regulators:behavioral
regulators:metabolic
conformers:variable environment
conformers:constant environment
Thermoregulation: Not all organisms work to maintain Steady State!
Conformers = Equilibrium Regulators = Steady State
Behavioral Thermoregulation = homeostasis (sometimes)T
em
per
atu
re (
ºC)
Time of daysunsetsunrise
Temperature in burrow
Air temperature nearground surface
Body temperature
regulators:behavioral
regulators:metabolic
Thermoregulation: Regulators work to maintain Steady State!
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Metabolic Effector Mechanisms:Too Cold? -> Generate more heat
Shivering (mammals, birds, bees, snakes):
= muscle contraction without power -> heat!
Heater Tissues (brown fat, bird muscles, tuna heads)= metabolic activity without products -> heat
mitochondria (heaters)fat (fuel)
Requires Metabolic Energy!
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Metabolic Effector Mechanisms:Too Hot? -> Dissipate heat
Evaporative Cooling:
Sweating (mammals)= actively pump out water
sweat glands
Panting (mammals & birds)= force air over wet surface
Requires Metabolic Energy!
Signal = Physiological Parameter (temperature)
1. Sensor (thermometer)
information= value of parameter
2. Integrator (thermostat)compare value to set point
Control Signal= deviation from set point
3. Effector (heater)
Negative Feedback:change parameter=> reduce deviation from set point
Control Systems & Homeostasis: Negative Feedback
= Stabilizing Control
‘Set Point’ (internal info)
‘Value’ (external info)
Feedback & mammalian thermoregulation
Homeostasis:normal body temperature
toohigh
toolow
Signal:Body Temperature
Sensor &Integrator= Hypothalamus
Negative Feedback= homeostasis!
Control Signals
Signal: Body Temperature
Sensor &Integrator= Hypothalamus
Control Signals
Negative Feedback= homeostasis!
Effectors
vasodilate
sweat
Effectors
vasoconstrict
shiver
temp falls
temp rises
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Positive Feedback = One-Way, Irreversible ChangesClot -> platelet activation -> clotting -> platelet activation -> etc=> Stop Bleeding!
hormone causesuterus to contract…
..that puts pressure on the cervix…
…that stimulates release of more hormone
…that causes uterus to contract more
..that puts more pressure on the cervix…
etc, etc
the baby comes out!
Irreversible Changes: Positive Feedback Control
Destabilizing Control