Basic Principles of Animal Form and Function

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negative feedback

Response:

Heater

turned

off

Stimulus:

Control center

(thermostat)

reads too hot

Room

temperature

decreases

Set

point:

20ºC

Room

temperature

increases

Stimulus:

Control center

(thermostat)

reads too cold

Response:

Heater

turned

on

Slide 34

Feedback Loops in Homeostasis

The dynamic equilibrium of homeostasis is maintained by negative feedback, which helps to return a variable to either a normal range or a set point.

Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off.

Positive feedback loops occur in animals, but do not usually contribute to homeostasis. Instead, positive feedback escalates a trend.

Slide 35

Alterations in Homeostasis

Set points and normal ranges can change with age or show cyclic variation.

Homeostasis can adjust to changes in external environment, a process called acclimatization.

Slide 36

Homeostatic processes for thermoregulation involve form, function, and behavior

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

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 non-avian reptiles

Slide 37

In general, ectotherms tolerate greater variation in internal temperature, while endotherms are active at a greater range of external temperatures.

Endothermy is more energetically expensive than ectothermy.

Slide 38

(a) A walrus, an endotherm

(b) A lizard, an ectotherm

Slide 39

Variation in Body Temperature

The body temperature of a poikilotherm varies with its environment, while that of a homeotherm is relatively constant.

Balancing Heat Loss and Gain:

Organisms exchange heat by four physical processes: conduction, convection, radiation, and evaporation.

Heat regulation in mammals often involves the integumentary system: skin, hair, and nails.

Slide 40

Heat exchange between an organism and its environment

Radiation

Evaporation

Convection

Conduction

Slide 41