UNIVERSITY OF NORTHERN PHILIPPINES
MASTER OF ARTS IN NURSING
CONSTANCYOF INTERNAL ENVIRONMENT
• Homeostasis is the maintenance of a “ steady
state “ condition (HOMEO = same and STASIS =
maintaining ). The body tries to maintain
homeostasis in regard to body
temperature, blood pH, etc.
• Homeostasis is the property of a system either
open or closed that regulates its internal
environment and tends to maintain a
stable, constant condition.
• Homeostasis is the process by which organisms
maintain a relatively stable environment despite
changes in the external environment.
Maintenance of a constant internal environment
is important for optimal metabolic efficiency. If
the internal environment is relatively stable, this
allows for a high level of efficiency for the
running of cells, such as enzymes having their
optimum pH and temperature conditions.
• Life is a series of chemical reactions. The sum of
all chemical reactions is called metabolism.
Metabolism is a series of chemical reactions that
occur in a specific order. In the human
body, thousands of chemical reactions take
place. The sequence takes a little under 24 hours
and then the whole thing starts over again and
occurs each and every day. In other
words, everyday, a particular sequence of
chemical reactions take place in the body in a
precise exacting manner.
• For this sequence to occur exactly the way it’s
supposed to, the internal environment of the
body has to be maintained so that the
environment is suitable for these reactions to
occur. The chemical reactions will only occur at
certain osmotic pressures and at certain
concentration of fluids. The chemical reactions
need to occur at a specific speed to allow other
reactions to occur.
• The control of cellular function by any hormone depends
on a series of reactions working through negative
feedback mechanisms. Hormone secretion is dependent
on the need of the body for the final action of that
hormone. When a body condition starts to move away
from the normal range and a specific action or response
is needed to correct this change, reaction of the
hormone capable of causing the correcting action or
response is stimulated until the need (demand) is met.
As the correction occurs, hormone secretion decreases
(and may halt). This type of control for hormone
synthesis is “negative feedback” because the hormone
causes the opposite action of the initial condition
• An example of a simple negative feedback
hormone response is the control of insulin
secretion. When blood glucose levels start to rise
above normal, the hormone insulin is secreted.
Insulin increases glucose uptake by the
cells, causing a decrease in blood glucose levels.
Thus the action of insulin (to decrease blood
glucose levels) is the opposite of the condition
that stimulated insulin secretion(elevated blood
• The Adaptive Mechanism Concept is a biochemical
extrapolation of Hans Selye’s pioneering endocrine
research into the body’s biochemical response to stress.
• Selye has defined stress as “the nonspecific response of
the body to any demand made upon it”. Whenever the
body is required to adopt, it must re-establish
homeostasis. It doesn’t matter in physiological terms
whether the stressor is pleasant or unpleasant. What
counts is the intensity, duration, and frequency of the
demand for readjustment or adaptation.
• The central theme of Selye’s research indicates that the
body responds in a stereotyped fashion to cope with any
type of increased demand upon the human machinery.
Selye described this response as the General Adaptation
Syndrome. In countless experiments, he found that the
body reacted in three consecutive ways: 1) by enlarging
the adrenal cortex, 2) shrinking the
thymus, spleen, lymph nodes and all other lymphatic
structures, and 3) by developing GI ulcers. He further
postulated that these reactions evolved trough the Alarm
Stage, the Resistance Stage, and the Exhaustion Stage.
• Selye proposed that “an essential feature of the
adaptation process is the confinement of stress to the
smallest area capable of meeting the requirements of a
situation. In the Alarm Stage, the body’s defenses are put
on general alert. During the Resistance Stage, the body
attempts to concentrate its efforts at the site of demand.
This localized effort continues until either homeostasis is
achieved or the resources of that area are exhausted.
Once local exhaustion occurs, the body draws on the
resources of the neighboring tissues or organs, initiating
another cycle of the Three Stages of the General
• The stress response is a mechanism by organisms to adapt and
overcome a stress stimulus in order to preserve homeostasis.
While facilitating survival, the stress response has become
associated with a plethora of maladies for modern man
suggesting it has maladaptive qualities. In considering the
physiological process and its contribution to survival, this
essay will argue that stress response cannot be considered a
single response to a single system. It needs to be viewed as
different variables in different systems with complex
interactions between the physiological and psychological. The
stress response may be modified by subjective perception of a
real or imagined stimulus. This may offer a means of
intervening in the stress response to mitigate against adverse
• It is quite true that environment has a direct
impact on those living in it and many diseases
are the outcome of man’s maladjustment to his
environment. The factors which affect human
health and cause disease, can be divided into
1. Intrinsic or Internal factors
2. Extrinsic or External factors
• The factors such as malfunctioning of the body
parts, hormonal imbalances, malfunctioning of
immune system and genetic disorders which
exist within the human body, are called Intrinsic
Factors. The disease caused by intrinsic factors is
called organic diseases or metabolic diseases.
Some examples of diseases caused by intrinsic
factors are: Heart attack, kidney
failure, cataract, diabetes mellitus, etc.
• The factors such as malnutrition, disease
causing microorganisms, environmental
pollutants, use of tobacco, alcohol and
narcotics, which exist outside of the
human body, are called Extrinsic Factors.
Some examples of diseases caused by
extrinsic factors are
Kwashiorkor, Goiter, Cholera, Tetanus, etc.