The term is most often used in the sense of biological
homeo- similar or same.
stasis- standing or stopping.
Multicellular organisms require a homeostatic internal
environment, in order to live; many environmentalists believe
this principle also applies to the external environment.
Many ecological, biological, and social systems are
homeostatic. They oppose change to maintain equilibrium. If the
system does not succeed in reestablishing its balance, it may
ultimately lead the system to stop functioning.
Complex systems, such as a human body, must have
homeostasis to maintain stability and to survive. These systems
do not only have to endure to survive; they must adapt
themselves and evolve to modifications of the environment.
Properties of homeostasis Homeostatic systems show several
They are ultrastable; Their whole organization, internal,
structural, and functional, contributes to the maintenance of
equilibrium They are unpredictable (the resulting effect of a
precise action often has the opposite effect to what was
expected). Main examples of homeostasis in mammals are as
The regulation of the amounts of water and minerals in the
body. This is known as osmoregulation. This happens in the
kidneys. The removal of metabolic waste. This is known as
excretion. This is done by the excretory organs such as the
kidneys and lungs. The regulation of body temperature. This
is mainly done by the skin. The regulation of blood glucose
level. This is mainly done by the liver and the insulin secreted
by the pancreas.
Mechanisms of homeostasis: feedback Main article: Feedback
When a change of variable occurs, there are two main types of
feedback to which the system reacts:
Negative feedback is a reaction in which the system responds
in such a way as to reverse the direction of change. Since this
tends to keep things constant, it allows the maintenance of
homeostasis. For instance, when the concentration of carbon
dioxide in the human body increases, the lungs are signalled to
increase their activity and expel more carbon dioxide.
Thermoregulation is another example of negative feedback. When
body temp rises (or falls), receptors in the skin and the
hypothalamus sense a change, triggering a command from the
brain, which in turn effects the correct response, this case
being body temp decreases.
In positive feedback, the response is to amplify the change
in the variable. This has a de-stabilizing effect, so does not
result in homeostasis. Positive feedback is less common in
naturally occurring systems than negative feedback, but it has
its applications. For example, in nerves, a threshold electric
potential triggers the generation of a much larger action
potential. (See also leverage points.) Blood clotting and events
in childbirth are other types of positive feedback.
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