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

2. Homeostasis and Thermoregulation
Chapter 32
Homeostasis and Thermoregulation

3. You Must Know The importance of homeostasis and examples.
How feedback systems control homeostasis.
One example of negative feedback control. (Thermoregulation)

4. 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.

5. Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus.
Sensor/
control center:
Thermostat
turns heater off.
Response:
Heating stops.
Room
temperature
decreases.
Stimulus:
Room
temperature
increases.
Set point:
Room temperature
at 20C
Set point:
Room temperature
at 20C
Regulation of room temperature by a thermostat is analogous to maintaining homeostasis via negative feedback.
Animals achieve homeostasis by maintaining a variable at or near a particular value, or set point.
Fluctuations above or below the set point serve as a stimulus; these are detected by a sensor and trigger a response.
The response returns the variable to the set point. Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus.
Stimulus:
Room
temperature
decreases.
Room
temperature
increases.
Response:
Heating starts.
Sensor/
control center:
Thermostat
turns heater on. 5

6. (temperature conformer)
Faced with environmental fluctuations, animals manage their internal environment by either regulating or conforming. 40
Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range.
River otter (temperature regulator) 30
Body temperature (C) 20
Largemouth bass
(temperature conformer)
An animal that is a regulator uses internal mechanisms to control internal change despite external fluctuation.
An animal that is a conformer allows its internal condition to change in accordance with external changes.
An animal may regulate some internal conditions and not others.
For example, a fish may conform to surrounding temperature in the water, but it regulates solute concentrations in its blood and interstitial fluid (the fluid surrounding body cells). 10 10 20 30 40
Ambient (environmental) temperature (C) 6

7. Ectotherm Endotherm Ectotherm Ectotherm Endotherm
Endothermic animals generate heat by metabolism; birds and mammals are endotherms.
Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles.
Ectotherm
Ectotherm
Endotherm 7

8. 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.

9. Radiation Evaporation Convection Conduction Figure 32.6
Organisms exchange heat by four physical processes
Radiation
Evaporation
Convection
Conduction
Heat is always transferred from an object of higher temperature to one of lower temperature
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises.
Conduction is the process by which heat energy is transmitted through collisions between neighboring molecules. Think of a frying pan set over an open camp stove. The fire's heat causes molecules in the pan to vibrate faster, making it hotter.
Convection
Conduction 9

10. Circulatory Adaptations for Thermoregulation
In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skin.
Vasodilation, the widening of the diameter of superficial blood vessels, promotes heat loss
Vasoconstriction, the narrowing of the diameter of superficial blood vessels, reduces heat loss

11. Acclimatization in Thermoregulation
Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes.

12. Sensor/control center: Thermostat in hypothalamus Response: Sweat
Figure 32.8
Sensor/control center: Thermostat
in hypothalamus
Response: Sweat
Response:
Blood vessels
in skin dilate.
Stimulus:
Increased body
temperature
Body
temperature
decreases.
Homeostasis:
Internal body
temperature of
approximately
36–38C
Homeostasis:
Internal body
temperature of
approximately
36–38C
Body
temperature
increases.
Stimulus:
Decreased body
temperature
Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus.
The hypothalamus triggers heat loss or heat-generating mechanisms.
Fever is the result of a change to the set point for a biological thermostat.
Response:
Blood vessels
in skin constrict.
Sensor/control center: Thermostat
in hypothalamus
Response: Shivering 12

13. There are two major systems for controlling and coordinating responses to stimuli: the endocrine and nervous systems.
Response
Hormone
Signal
travels
everywhere.
Stimulus
Blood
vessel
Endocrine
cell
(a) Signaling by hormones
Cell
body of
neuron
Nerve
impulse
Signal
travels to
a specific
location.
Response
Stimulus
Axons
Axon
(b) Signaling by neurons
Signaling molecules sent out by the endocrine system are called hormones.
Hormones may have effects in a single location or throughout the body.
Only cells with receptors for a certain hormone can respond to it.
The endocrine system is well adapted for coordinating gradual changes that affect the entire body.
In the endocrine system, signaling molecules released into the bloodstream by endocrine cells reach all locations in the body.
In the nervous system, neurons transmit signals along dedicated routes, connecting specific locations in the body. 13