Basic Principles of Animal Form and Function

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A hormone may affect one or more regions throughout the body.

Hormones are relatively slow acting, but can have long-lasting effects.

Slide 26

Signaling

Stimulus

Hormone

Endocrine

cell

Signal travels

everywhere

via the

bloodstream.

Blood

vessel

Response

(a) Signaling by hormones

Stimulus

Neuron

Axon

Signal

Signal travels

along axon to

a specific

location.

Signal

Axons

Response

(b) Signaling by neurons

Slide 27

The nervous system transmits information between specific locations.

The information conveyed depends on a signal’s pathway, not the type of signal.

Nerve signal transmission is very fast.

Nerve impulses can be received by neurons, muscle cells, and endocrine cells.

Slide 28

Stimulus

Neuron

Axon

Signal

Signal travels

along axon to

a specific

location.

Signal

Axons

Response

Signaling by neurons

Slide 29

Feedback control loops maintain the internal environment in many animals

Animals manage their internal environment by regulating or conforming to the external environment.

A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation.

A conformer allows its internal condition to vary with certain external changes.

Slide 30

River otter (temperature regulator)

Largemouth bass

(temperature conformer)

Body temperature (°C)

0

10

10

20

20

30

30

40

40

Ambient (environmental) temperature (ºC)

Slide 31

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.

Slide 32

Mechanisms of homeostasis moderate changes in the internal environment.

For a given variable, fluctuations above or below a 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. Negative Feedback acts to reverse a trend… To maintain the variable within a narrow range.

Mechanisms of Homeostasis

Slide 33