This document summarizes stress physiology and the physiological response to stressors in animals. It defines stress, strain, and stressors. It describes the general adaptation syndrome and its three stages: alarm reaction, resistance, and exhaustion. It discusses different types of environmental stressors like temperature, oxygen availability, and salinity. It explains the nature of interaction with stressors through tolerance, resistance, acclimation, and acclimatization. It also summarizes the physiological responses to stress like increased heart rate and blood pressure, immune suppression, and catabolic actions.

1. Stress Physiology
By:
D.Gayathri
University of Madras

2. Objective:
To understand the physiological principles
concerned with compensation in animals against
environmental stressors.
To understand the general stages of adaptation.

3. 1.)What is Stress ?
2) What is strain?
3.)What are Stressors?
4.)Environmental stressors
5.)Nature of interaction with environmental
stressors.
6)Elastic and plastic strain
7)Physiological compensation to altered
environments.
8.)Stress response system
9.)General adaptation syndrome
10.)Physiological response to stress
9.)Conclusion
10.)Objective questions
11.)Answer key
12.)References

4. WHAT IS STRESS
 Hans Selye coined the word, “stress,” in
1936.
Definition: “non-specific response of the
body of organism to any demand for
change.”
 In terms of environmental physiology,
Stress can be best defined as
environmental pressures which requires
physiological compensation, which are
functional properties of organisms which
favour their continued successful living in
altered environments.(C.L.Prosser)

5. What is strain?
Strain in general is the change produced in response
to the stress.
In terms of environmental physiology, strain is the
functional property of an organism to resist and
survive under environmental stress (i.e) physiological
adaptation (or) compensatary response to the
external stressor.

6. Stressors are factors that challenge the homeostasis of organism resulting in stress.
TYPES
a) External Stressors.
Ex: Temperature, Salinity, Oxygen availability, etc.,
b) Internal Stressors.
Ex: Life-style changes, Negative-self talks, Mind traps, etc.,
Here we are going to focus on external environmental stressors, which alter the
internal homeostasis of organisms in distinct ways according to nature of stressor and
mechanism of stress response elucidated by it.
WHAT ARE STRESSORS?

7. Environmental stressors:
Temperature: Temperature change frequentlly produces a prompt, direct and proportional
alteration in the rate of physiological process within animal’s zone of tolerance.
Ex: For example, in hot springs there may be thermophilic bacteria living at temperatures in excess
of 90°C, but for metazoans the upper limits are set well below this: for land animals the upper limits
are attained by certain desert insects and reptiles, in which body temperature may sometimes exceed
50°C; for aquatic invertebrates maximum heat tolerance occurs in some specialized ostracod
crustaceans, which can tolerate 49°C for short periods; and among the vertebrates a few species of
fish can thrive at 44°C.
Thus, from the above example we can infer that each organism has its own adaptation to thrive
within a zone of temperature tolerance by manitaining homeostasis using different adaptations.

8. Oxygen availability: oxygen is indispensable to oxidative
phosphoryration, and below certain minimal levels the
production of ATP is curtailed; the metabolism and activities of
animals are limited in accordance.
Ex: Aerobic animals which require adequate oxygen for their survival
Animals which survive in low oxygen levels occasionally (or)
continuously for a long time Facultative Anaerobes, which switch to
aerobic metabolism when oxygen is available.
The animals which never require oxygen are Obligate Anaerobes.

9. Salinity: It is an important factor in the maintenance
of ionic and osmotic balance of organism.
Ex: Stenohaline and Euryhaline organisms. The
former thrive in extremely low salinity like fresh
water teleosts, and the latter thrive in high salinity
concentrations like halophilic bacteria and artemia
species.

10. Nature of Interaction with
Environmental stressors:
Tolerance
Resistance
Acclimation
Acclimatization

11. Tolerance:
Every animal has the capacity to compensate for environmental
change as a part of its genetic endowment, provided this doesn’t
exceeds the range of tolerance.
Ex: Under normal conditions, a catfish can live at temperatures
ranging from 1⁰C to 35⁰C. This is its range of tolerance, beyond
or below which the animal dies after a resistance time

12. Resistance:
An animal makes a dynamic physiological response to environmental
changes at more extreme range beyond the zone of tolerance which is
zone of Resistance.
Ex: Polar bears living at extremley cold arctic regions, Artemia
species living at extreme salinities upto 200% SW

13. Acclimation:
It is the descriptive term applied to compensatory
changes which occur in animals which are maintained
under controlled conditions of the environmental
factors.
Ex: Compensatory changes which takes place in
animals such as rats and mice, when they are
maintained under controlled conditions in laboratory.

14. Acclimatization:
The term acclimatization is reserved for compensatory changes occuring
under natural conditions. It is the sum of the adjustments which follow
repeated and pro-longed exposure to natural environmental change.
Ex: 1)Migration up a mountain may lead to acclimatization to low
oxygen and low pressure,
2) salmon show seasonal changes in their temperature tolerance,
which are partly due to seasonal temperature cycle but may also be
associated with photo-period and other seasonally changing
conditions.

15. Elastic and Plastic strain
Elastic strain: Elasticity is a concept directly connected with the
deformation of materials. When an exterior stress is applied to body of organism, the
body tends to pull itself apart. This causes the distance between cells to increase. Each
cells tries to pull its neighbor as close as possible. This causes a force trying to resist the
deformation. This force is known as strain.
Ex: Jumping to any significant height again requires speed at take-off, which just as in
most arthropods involves a very rapid straightening of the “knee” joints (usually with a
preparatory bending of the legs), and employs built-in elasticity. Jumping involves
tendon and muscle changes, to allow for the elastic storage.

16. Plastic strain: Plasticity is a property of an animal’s system that allows it to deform
irreversibly. Plasticity can be broadly defined as the ability of one genotype to produce
more than one phenotype when exposed to different environments, as the modification of
developmental events by the environment, or as the ability of an individual organism to alter
its phenotype in response to changes in environmental conditions.
Ex: Predator avoidance, insect wing polymorphisms, the timing of metamorphosis in
amphibians, osmoregulation in fishes, and alternative reproductive tactics in male
vertebrates.
From a human health perspective, documented examples of plasticity most commonly
include the results of exercise, training, and/or dieting on human morphology and
physiology.

17. Physiological Compensation
to Altered Environment
There are three different kinds of physiological
compensation for successful living in altered
environment. They are as follows:
Avoiders
Conformers
Regulators

18. 1. Avoiders: These are organisms that have some mechanism for
getting away from an environmental problem either in space or in
time.
Ex: for space- (e.g. seeking unstressed microhabitats in crevices or
burrows, or larger scale migration)
for time- (using torpor or diapause, or producing a resistant egg, pupa,
or cyst to survive difficult times).
2. Conformers: These are organisms which undergo changes of
internal state similar to the changes of state imposed externally.
(They are therefore sometimes termed “tolerators”, “tolerating” the
external conditions in the sense that they are surviving in them.)
Conformers do not attempt to maintain a homeostatic condition for
the whole body.
3. Regulators: These are organisms which maintain all the
components of their internal environment close to the original or
“normal” level, irrespective of external conditions.

21. Stages of General Adaptation syndrome

22. General Adaptation Syndrome
 Stage I - Alarm Reaction
◦ When the stressor or
threat is identified, the
body’s response is a state
of alarm.
◦ Ex: Release of
adrenaline in order to
bring the “fight or flight”
response 12/31/2015 22

23.  Stage II – Stage of Resistance
◦ If stressor persists, the organism tries
to adapt to continued challenges
utilizing available resources.
◦ It decreases the effectiveness of the
immune system which makes you more
susceptible to diseases.
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24.  Stage III – Stage of Exhaustion
◦ Stress persists for a long time
◦ Environmental demands or
strains exceeded available
resources
◦ All the body’s available
resources are eventually
depleted and the body is unable
to maintain normal function.
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25. Physiological response to
stress:
During acute stress, the heart rate and arterial blood pressure are increased,
while gluconeogenesis, glycogenolysis, lipolysis and hepatic glucose secretion
are stimulated, owing to elevated levels of catecholamines and cortisol.
 Suppress the immune system, Stress has complex effects on the immune
system and influences both innate and acquired immunity. Glucocorticoids
and catecholamines influence trafficking and/or function of leukocytes and
accessory immune cells and suppress the secretion of proinflammatory
cytokines (tumor necrosis factor [TNF], IL-1, IL-6, IL-8 and IL-12), whereas
both hormone families induce a systemic switch from a TH1 response (that is,
cellular immunity) to a TH2 response (humoral immunity).
 Direct catabolic actions, glucocorticoids also antagonize the beneficial
anabolic actions of GH, insulin and sex steroids on their target tissues .
 Stress can speed up the aging process. Long-term stress can even rewire
the brain, leaving more vulnerable to anxiety and depression.

26. Schematic representation of the interactions between the hypothalamic-pituitary-
adrenal axis and the thyroid and immune function. CRH: corticotropin-releasing
hormone, STS: somatostatin, TRH: thyrotropin releasing hormone, TSH: thyroid
stimulating hormone, T4: thyroxine, T3: triiodothyronine, TNF-α: tumor necrosis
factor-α, IL-1: interleukin-1, IL-6: interleukin-6. Activation is represented by
solid green lines and inhibition by dashed red lines.

27. Schematic representation of the interactions between the stress and the
immune system. LC/NE: locus ceruleus/norepinephrine-sympathetic system,
SPGN: sympathetic postgaglionic neurons, CRH: corticotropin-releasing
hormone, AVP: arginine vasopressin, ACTH: corticotrophin, PAF: platelet
activating factor, NE/E: norepinephrine/epinephrine,: Th1: T-helper
lymphocyte 1, Th2: T-helper lymphocyte 2. Stimulation is represented by solid
green lines and inhibition by dashed red lines.

28. Stress Contribute to infertility
Schematic representation of the detrimental effects of chronic stress on
adipose tissue, bone and muscle metabolism. GH: growth hormone.
Stimulation is represented by solid green lines and inhibition by dashed
red lines.

29. Conclusion:
Many animals in a gradient of an environmental variables such as temperature, ionic balance,
oxygen availability, pressure, light, etc., will move about while they are in less favourable areas and
remain quiet when they arrive in the more favourable areas.
 The environment in this case is acting as “Directive force” and the variables are the
“Environmental stressors.”
The preferendum response to these “stress” results in adaptations which may be either elastic or
reversable strain (or) plastic or irreversable strain.
 The functional properties of animal which help them to survive better in stressful environment is
the “Physiological compensation or Strain ”. Thus, the physiological compensation achieved against
environmental stressor is termed as “Environmental Stress Physiology.”

30. Objective Questions
1) The force which demands for change in body regulation is……..
a)Stimuli b)Strain
c)Force d) Stress
2)The response of body to change in environment is……..
a)Response b)acclimation
c) Strain d)resistance.
3)Which of following is scientist who coined word stress?
a)Newton b)Darwin
c)Hans sleye d)Lamarck
4)………….is defined as irreversible deformation of body.
a)Plastic strain b)Elastic strain
c)Adaptation d) Stress
5)………….is the controler of stress response mechanism.
a)Pitutary gland b)hypothalamus
c)Adrenal gland d)thyroid gland.

31. 6) ………..is harmone released by hypothalamus to stimulate adrenal gland.
a)Corticotropin b)adrenalin
c)ADH d)oxytosin
7)Stages of stress adaptation is called…….
a)General adaptation syndrome
b)Adaptation
c)Physiological response
d)Compensation
8)………..is the example for organism surviving at high salinities.
a)Arulla b)Physalia
c)Artemia d)teleosts
9)………….are produced by adrenal gland in response to stress.
a)Corticosteroids b)adrenalin
c)Thyroxine d)androgen
10)……………… is terminology for organism thriving at extreme salinities.
a)Stenohaline b)Euryhaline
c)Hyperosmotic d)Hypoosmotic

32. References:
William Hoar, S.1992. General and Comparitive Physiology
(2nd edition).
 Pat willmer, Graham stone & Ian Johnston. 2005. Environmental physiology of
animals, Black well Publishing Company, Australia.
Fehrenbach, E. 2005. Cellular response to environmental stress. In:Molecular and
Cellular Exercise Physiology. (Mooren, F., Volker, K.) Human Kinetics, Champaign IL.
Phenotypic Plasticity: Molecular Mechanisms and Adaptive Significance
Scott A. Kelly, Tami M. Panhuis, Andrew M. Stoehr
http://physiology.grad.ncsu.edu/environmental-stress-physiology
http://as.wiley.com/WileyCDA/Section/id-404531.html
https://en.wikipedia.org/wiki/Ecophysiology