2. Life = “Steady State” Food Water O2 Heat Feces Urine CO2 Heat
Constancy of Internal Environment:
HOMEOSTASIS
“Delicate Balance” = Regulation

3. Temperature It’s good to be constant

4. Homeotherm Heterotherm constant body temp body temp varies
with environment
Body temperature (ºC)
Environmental temperature (ºC)

5. Thermoregulation: Not all organisms work to maintain Steady State!
Conformers = Equilibrium
Regulators = Steady State
regulators:
metabolic
conformers:
variable environment
regulators:
behavioral
conformers:
constant environment

6. Behavioral Thermoregulation = homeostasis (sometimes)
Body temperature
Temperature (ºC)
Air temperature near
ground surface
Temperature in burrow
Time of day
sunrise
sunset

8. Thermoregulation: Regulators work to maintain Steady State!
metabolic
regulators:
behavioral

10. 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!

11. Metabolic Effector Mechanisms: Too Hot? -> Dissipate heat
Evaporative Cooling:
Panting (mammals & birds)
= force air over wet surface
Sweating (mammals)
= actively pump out water
sweat glands
Requires Metabolic Energy!

12. Control Systems & Homeostasis: Negative Feedback
Signal = Physiological Parameter (temperature)
Negative Feedback:
change parameter
=> reduce deviation from set point
1. Sensor (thermometer)
information
= value of parameter
‘Set Point’ (internal info)
‘Value’ (external info)
3. Effector (heater)
2. Integrator (thermostat)
compare value to set point
Control Signal
= deviation from set point
= Stabilizing Control

13. normal body temperature
Feedback & mammalian thermoregulation
Control Signals
Sensor &
Integrator
= Hypothalamus
Effectors
vasodilate
sweat
temp
falls
Signal:
Body Temperature
Negative Feedback
= homeostasis!
too
high
Homeostasis:
normal body temperature
Negative Feedback
= homeostasis!
too
low
Signal:
Body Temperature
temp
rises
Effectors
vasoconstrict
shiver
Control Signals
Sensor &
Integrator
= Hypothalamus

14. Positive Feedback = One-Way, Irreversible Changes
Clot -> platelet activation -> clotting -> platelet activation -> etc
=> Stop Bleeding!

15. Irreversible Changes: Positive Feedback Control
..that puts pressure on the cervix…
hormone causes
uterus to contract…
…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!
Destabilizing Control