Biology 12

Chapter 6 The Endocrine System • MHR 189

Fight or Flight Syndrome

In Chapter 5, the “fight or flight” syndrome was
discussed in the context of nervous system function.
The fight or flight reaction is the way in which the
body responds to a sudden, unexpected stressful
stimulus, such as a physical threat or some other
perceived emergency situation. This reaction is
produced by the rapid release of adrenaline and
noradrenaline by the adrenal gland (which reinforces
the action of the sympathetic nervous system).
For example, if you were to notice that you were
in the path of a rapidly oncoming car or if you came
face to face with a bear in the woods, your breathing
rate and heart rate would quickly increase. You
would also experience a rapid elevation in blood
sugar level.
In our human ancestors, this reaction would have
been induced primarily by a perception of physical

danger. However, stress can also be triggered by

feelings of excitement, anxiety, psychological

conflicts, environmental extremes (such as severe

heat or cold), or a lack of sleep.

The phrase “fight or flight response” was coined

by Walter B. Cannon and Hans Selye, a Canadian

doctor, in the 1930s. The phrase defines the pattern

of physiological responses that prepares the body

for emergency situations. Cannon studied the effect

of stress on dogs, observing that stress depressed

digestive function. His work led him to develop the

concept of homeostasis. Much of Selye’s research

focussed on how the adrenal gland affects the

body’s immune and inflammatory responses during

times of stress.

Conduct Investigation 6-A to see how animals

are affected by the stress caused by situations of

overcrowding.

3.Design an experiment that can be carried out in the

classroom.

4.Outline a procedure for your experiment, listing each

step. Assemble the materials you will require.

5.Decide what observations you will make and a

method to quantify them.

Checking the Plan

1.What will be your independent variable? What will

be your dependent variable(s)? What will be your

controlled variable(s)?

2.Does your method of collecting data allow for a

number of different responses to crowding?

3.Has your teacher approved your plan?

Data and Observations

Conduct your experiment and record your results.

Present your data in a graph or chart that will help you

communicate your findings to other groups in the class.

Analyze

1.What was the size of the population(s) at the

beginning of the experiment?

2.Did the population(s) increase? If so, at what rate?

3.Did the ratio of males to females change?

4.Were the fish randomly distributed throughout

the tank?

5.Was there any observable aggressive behaviour?

Conclude and Apply

6.Were your results consistent with those obtained by

other groups in your class? Explain.

7.Is there any evidence that crowding affected the

endocrine system of the fish?

Exploring Further

8.Using the results from your experiment, form a new

hypothesis and an experiment to test it.