Page 6 - 84 human physiolofy part-1

Chapter 1

maintenance of balance.

• Physiology is largely a study of processes related to homeostasis. Some of the functions
you will learn about in this book are not specifically about homeostasis (e.g. how muscles
contract), but in order for all bodily processes to function there must be a suitable internal
environment. Homeostasis is, therefore, a fitting framework for the introductory study of
physiology.

Where did the term "Homeostasis" come from?

The concept of homeostasis was first articulated by the French scientist Claude Bernard (1813-
1878) in his studies of the maintenance of stability in the "milieu interior." He said, "All the vital
mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life
in the internal environment" (from Leçons sur les Phénonèmes de la Vie Commune aux Animaux et aux
Végétaux, 1879). The term itself was coined by American physiologist Walter Cannon, author of The
Wisdom of the Body (1932). The word comes from the Greek homoios (same, like, resembling) and
stasis (to stand, posture).

Cruise Control on a car as a simple metaphor for homeostasis

When a car is put on cruise control it has a set speed limit that it will travel. At times this speed
may vary by a few miles per hour but in general the system will maintain the set speed. If the car starts
to go up a hill, the systems will automatically increase the amount of fuel given to maintain the set
speed. If the car starts to come down a hill, the car will automatically decrease the amount of fuel given
in order to maintain the set speed. It is the same with homeostasis- the body has a set limit on each
environment. If one of these limits increases or decreases, the body will sense and automatically try to
fix the problem in order to maintain the pre-set limits This is a simple metaphor of how the body
operates--constant monitoring of levels, and automatic small adjustments when those levels fall below
(or rise above) a set point.

Pathways That Alter Homeostasis

A variety of homeostatic mechanisms maintain the internal environment within tolerable limits.
Either homeostasis is maintained through a series of control mechanisms, or the body suffers various
illnesses or disease. When the cells in your body begin to malfunction, the homeostatic balance
becomes disrupted. Eventually this leads to disease or cell malfunction. Disease and cellular
malfunction can be caused in two basic ways: either, deficiency (cells not getting all they need) or
toxicity (cells being poisoned by things they do not need). When homeostasis is interrupted in your
cells, there are pathways to correct or worsen the problem. In addition to the internal control
mechanisms, there are external influences based primarily on lifestyle choices and environmental
exposures that influence our body's ability to maintain cellular health.

• Nutrition: If your diet is lacking in a specific vitamin or mineral your cells will function
poorly, possibly resulting in a disease condition. For example, a menstruating woman with
inadequate dietary intake of iron will become anemic. Lack of hemoglobin, a molecule that
requires iron, will result in reduced oxygen-carrying capacity. In mild cases symptoms may be

6 | Human Physiology