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