UNIT
2 Homeostasis
In 1775, Dr. Charles Blagden of the Royal Society of
London tested the human body’s ability to withstand
heat. He had a special room heated to 126°C, well
above the boiling point of water. He then entered
the room with a pet dog and a piece of raw meat.
After 45 minutes, he left the room with no ill effects
other than a pulse rate that had increased to 144
beats per minute (about twice its normal rate). The
dog, too, was fine, but the meat had been cooked.
As the results of Dr. Blagden’s experiment
indicate, the body has developed physiological and
biochemical mechanisms that allow it to maintain
its internal physiological environment in a relatively
stable state. It is able to do so in the face of external
stresses such as high or low temperatures and
internal stresses such as fever and infection. There
are limits to the extent of stress with which these
mechanisms can cope, however. For example, long
workouts in unusually hot, humid conditions can
result in heat exhaustion, which, in one case, led to
the death of a football player.
Individual differences also play a significant
role in determining the effectiveness of the body’s
mechanisms for regulating its internal environment.
Young children, the elderly, and heavy individuals,
for instance, are more likely to suffer from heat
exhaustion than others. In this unit, you will see
how these mechanisms on which we all depend,
in spite of individual differences, work together
to maintain the stable state within us.Unit
Contents
Chapter 4
Homeostatic
Mechanisms......
Chapter 5
The Nervous
System..........
Chapter 6
The Endocrine
System..........Unit Project......^208166136106104
Unit
Preview
In this Unit, you will
discover
the physiological and
biochemical mechanisms
involved in the maintenance
of homeostasis,
the feedback mechanisms
that maintain chemical
and physical homeostasis
in animal systems, and
how environmental factors
and technological
applications affect and
contribute to the main-
tenance of homeostasis,
and how they relate to
certain social issues.The very young and the very old are more
susceptible to internal and external stress.Look ahead to
pages 208–209.
You will be examining the
topic of treatments for
diabetes at the end of
this chapter.
Start gathering newspaper
clippings, magazine articles,
videos of television
specials, or web site
addresses that pertain
to this topic.UNIT PROJECT PREP