Chapter 2: The Physiology of Stress

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Chapter 2The Physiology of Stress

• To understand the stress response, we must
  possess a fundamental knowledge not only of
  psychology but of physiology as well.
  - George Everly

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The physiology of stress

• Hans Selye, considered by many as the father of
  the study of stress, developed the idea that
  there was a direct relationship between chronic
  stress and excessive wear and tear throughout the
  body.

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Psychophysiology

• is a term to describe the bodys physiological
  reaction to perceived stressors suggesting that
  the stress response is a mind-body phenomenon.

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The human brainis divided into three levels

• the vegetative level
• the limbic system
• the neocortical level

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The Nervous Systemcan be divided into

• the central nervous system (CNS)
• brain and
• spinal cord
• the peripheral nervous system (PNS)
• consists of all neural pathways to the
  extremities

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The vegetative level

• the lowest level of the brain is comprised
  of the
• reticular formation
• brain stem

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Reticular activating system (RAS)

• The RAS is the link connecting the brain to
  the spinal cord.
• Several stress physiologists believe that this
  is the bridge joining the mind and the body as
  one
• this organ functions as a communi- cation link
  between the mind and the body.

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The brain stem

• The brain stem, comprised of the pons, medulla
  oblongata, and mesencephalon, is responsible
  for involuntary functions of the human body
  such as
• heart beat
• respiration
• and vasomotor activity

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The limbic system

• The limbic system is the emotional control
  center and comprised of the
• thalamus
• hypothalamus
• pituitary gland
• also known as the master endocrine gland
• These three glands work in unison to maintain
  a level of homeostasis

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The neocortical level

• The neocortex is the highest level of the
  brain.
• It is at this level that sensory information is
  processed as a threat or a non-threat and where
  cognition takes place.
• This higher level of the brain can override a
  lower level and can influence emotional
  responses.

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Physiological systems involved in the stress
response

• the nervous system
• the endocrine system
• the immune system

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The autonomic nervous system(ANS)

• The ANS regulates visceral activities and vital
  organs, including
• circulation,
• digestion,
• respiration, and
• temperature regulation

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Two branches of the ANS that act to maintain
homeostatic balance

• the sympathetic
• parasympathetic

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The sympathetic and parasympathetic systems
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Sympathetic nervous system

• is responsible for the responses associated
  with the fight-or-flight response
• this physical arousal is stimulated through
  the release of catecholamines
• epinephrine (adrenaline)
• norepinephrine (noradrenaline)

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Parasympathetic nervous system

• maintains homeostasis through the release of
  acetylcholine (ACh)
• is responsible for energy conservation and
  relaxation

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The endocrine system

• consists of a series of glands located
  throughout the body which regulate metabolic
  functions that require endurance rather than
  speed
• the endocrine system is a network of four
  components
• glands, hormones, circulation, and target organs

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Endocrine system

• the glands most closely involved with the
  stress response are the
• pituitary,
• thyroid, and
• adrenal glands

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The nervous system and the endocrine system

• join together to form metabolic pathways or
  axes.
• there are three pathways
• the ACTH axis
• the vasopressin axis, and
• the thyroxine axis

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The ACTH pathways
stimulation of sensory nerves
pituitary
stressor
ACTH
hypothalamus
adrenal glands
stress hormones cortisol aldosterone epinephrine
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Three stages of effects associated with the
stress response

• Immediate effects of stress
• Intermediate effects of stress
• Prolonged effects of stress

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Immediate effects of stress

• sympathetic nervous response
• epinephrine and nor-epinephrine released
• time - 2 to 3 seconds
• like a phone call

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Intermediate effects of stress

• adrenal response
• epinephrine and nor-epinephrine release from
  adrenal medulla
• time- 20 to 30 seconds
• like a telegram

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Prolonged effects of stress

• ACTH, vasopressin and thyroxine affect various
  metabolic processes
• time - minutes, hours, days or weeks
• like an overnight delivery

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Immediate, intermediate, and prolonged effects of
stress
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