I have a meeting tomorrow morning. Computers or Natural Selection Lab tomorrow?

I have a meeting tomorrow morning.

Computers or Natural Selection Lab tomorrow?

Chapter 32Homeostasis and Thermoregulation

You Must Know

• The importance of homeostasis and examples.

• How feedback systems control homeostasis.

• One example of negative feedback control. (Thermoregulation)

Homeostasis

• Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment.

• In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level.

Sensor/control center:Thermostatturns heater on.

Stimulus:Room

temperaturedecreases.

Roomtemperatureincreases.

Set point:Room temperature

at 20C

Response:Heating starts.

Regulation of room temperature by a thermostat is analogous to maintaining homeostasis via negative feedback.

Sensor/control center:Thermostatturns heater off.

Stimulus:Room

temperatureincreases.

Roomtemperaturedecreases.

Set point:Room temperature

at 20C

Response:Heating stops.

Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus.

River otter (temperature regulator)

40

Largemouth bass (temperature conformer)

Ambient (environmental) temperature (C)

30

20

10

00 40302010

Bo

dy

tem

per

atu

re (C

)

Faced with environmental fluctuations, animals manage their internal environment by either regulating or conforming.

Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range.

Endotherm Ectotherm

Endotherm Ectotherm

Ectotherm

• Endotherms can maintain a stable body temperature in the face of large fluctuations in environmental temperature.

• Ectotherms may regulate temperature by behavioral means.

• Ectotherms generally need to consume less food than endotherms, because their heat source is largely environmental.

Figure 32.6Radiation

Convection

Evaporation

Conduction

• In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skin.

Circulatory Adaptations for Thermoregulation

• Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes.

Acclimatization in Thermoregulation

Figure 32.8

Stimulus:Decreased body

temperature

Bodytemperatureincreases.

Homeostasis:Internal body

temperature ofapproximately

36–38C

Response: Shivering

Sensor/controlcenter: Thermostatin hypothalamus

Response:Blood vesselsin skin constrict.

Sensor/controlcenter: Thermostatin hypothalamus

Bodytemperaturedecreases.

Homeostasis:Internal body

temperature ofapproximately

36–38C

Response:Blood vesselsin skin dilate.

Stimulus:Increased body

temperature

Response: Sweat

Response

Hormone

Signaltravelseverywhere.

Stimulus

Blood vessel

Endocrinecell

(a) Signaling by hormones

There are two major systems for controlling and coordinating responses to stimuli: the endocrine and nervous systems.

Cellbody ofneuron

Nerveimpulse

Signaltravels toa specificlocation.

Response

Stimulus

Nerveimpulse

Axons

Axon

(b) Signaling by neurons