Stress Physiology

By: D.Gayathri

University of Madras

Objective:To understand the physiological principles

concerned with compensation in animals against

environmental stressors.

To understand the general stages of adaptation.

1.)What is Stress ?2) What is strain?3.)What are Stressors?4.)Environmental stressors5.)Nature of interaction with environmental stressors.6)Elastic and plastic strain7)Physiological compensation to altered environments.8.)Stress response system9.)General adaptation syndrome10.)Physiological response to stress9.)Conclusion10.)Objective questions11.)Answer key12.)References

Content

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)

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.

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?

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.

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.

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.

Nature of Interaction with Environmental stressors:

ToleranceResistanceAcclimationAcclimatization

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 1 C to 35 C. This is its range of tolerance, ⁰ ⁰

beyond or below which the animal dies after a resistance time

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

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.

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.

Elastic and Plastic strainElastic 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.

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. 

Physiological Compensation to Altered

EnvironmentThere are three different kinds of physiological compensation for successful living in altered environment. They are as follows:

Avoiders

Conformers

Regulators

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.

Stages of General Adaptation syndrome

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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

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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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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.

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.

 

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.

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.

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.

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.”

Objective Questions1) The force which demands for change in body regulation is……..a)Stimuli b)Strainc)Force d) Stress

2)The response of body to change in environment is……..a)Response b)acclimationc) Strain d)resistance.

3)Which of following is scientist who coined word stress?a)Newton b)Darwinc)Hans sleye d)Lamarck

4)………….is defined as irreversible deformation of body.a)Plastic strain b)Elastic strainc)Adaptation d) Stress

5)………….is the controler of stress response mechanism.a)Pitutary gland b)hypothalamusc)Adrenal gland d)thyroid gland.

6) ………..is harmone released by hypothalamus to stimulate adrenal gland.a)Corticotropin b)adrenalinc)ADH d)oxytosin

7)Stages of stress adaptation is called…….a)General adaptation syndromeb)Adaptationc)Physiological responsed)Compensation

8)………..is the example for organism surviving at high salinities.a)Arulla b)Physaliac)Artemia d)teleosts

9)………….are produced by adrenal gland in response to stress.a)Corticosteroids b)adrenalinc)Thyroxine d)androgen

10)……………… is terminology for organism thriving at extreme salinities.a)Stenohaline b)Euryhalinec)Hyperosmotic d)Hypoosmotic

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 SignificanceScott 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