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N206
Define homoestasis-the purposeful maintenance of a stable internal environment by
coordinated physiologic processes that oppose change.-Walter B Cannon
The physiologic control systems that oppose change operate by _______
______ mechanisms.
Negative Feedback
Negative Feedback Mechanisms consist of what three systems?
1. Sensor: that detects a change
2. Integrator/comparator: that sums and compare incoming data with a set point
3. Effector: that returns the sensed function to within the range of the set point.
2. Integrator/comparator: that sums and compare incoming data with a set point
3. Effector: that returns the sensed function to within the range of the set point.
The ability of the body to function and maintain homeostasis under
conditions of change in the internal and external environment depends on the
thousands of phusiologic ________ _____ that regulate body function.
Control Systems
?What happens when you are too hot?
Vasodilation/Sweating
?How does your body tell you it is dehydrated?
Osmoreceptors send message to brain=thirst
What happens when your calcium level is too low?
We absorb more calcium from GI or bone.
What happens when your arterial ph is too low?
Respiratory system enhances itself to increase respiratory rate to
balance ph levels.
The control systems mediate the physical, emotional, and behavioral
reactions to stressors that, taken together, are called the ____ _____?
Stress Response
Most control systems in the body operate by _____ _____ mechanisms.
Negative Feedback
Why do most physiologic control systems function under negative rather
than positive feedback mechanisms?
Because positive feedback interjects instability rather than stability
into a system. The initiating stimulus produces more of the same.
Selye: Stress Definition?
a state manifested by a specific syndrome of the body developed in
response to any stimuli that made an intense systemic demand on it.
What does GAS stand for?
General Adaptation Syndrome-Selye
What does General stand for?
the effect was a general systemic reaction
Adaptive?
because the response was in reaction to a stressor.
Syndrome?
because the physical manifestations were coordinated and dependent on
each other.
What are the three stages of GAS?
Alarm stage, resistance stage, exhaustion stage
Alarm stage?
Stimulation of the sympathetic nervous system and the HPA axis
(hypothalamic pituitary adrenal), resulting in the release of catecholamines
and cortisol.
Resistance Stage?
The body selects the most effective and economic channels of defense.
Cortisol levels that were present during the first stage drop because they are
no longer needed.
Exhaustion Stage?
If the stressor is prolonged or overwhelms the ability of the body to
defend itself, exhaustion ensues. Systemic damage may appear. Ex. headaches.
The events or environmental agents responsible for intitiating the stress
response are called____.
Stressors
According to Selye, stressors can be ____ or ____?
Endogenous or Exogenous
Definition of Endogenous?
arising from within the body
Definition of Exogenous?
arising from outside the body
Two factors determine the nature of the stress response:??
1. the properties of the stressor
2. the conditioning of the person being stressed.
2. the conditioning of the person being stressed.
Two types of stress?
Eustress and distress
Eustress?
mild, brief, and controllable periods of stress could be positive
stimuli to emotional and intellectual growth.
Distress?
severe, protracted, and uncontrolled situations of psychological and
physical distress/disruptive to health.
Conditioning Factors-Selye? Two types?
Internal and external
Give an example of an internal conditioning factor-way a person responds
to different stressors?
genetic predisposition, sex, age
Give and example of an external conditioning factor?
environmental agents, life experiences, dietary factors, level of social
support
What are the three basic steps of the Neuroendocrine response to stress?
1. Signals are received from neurosensory pathways
2. Alert that there is a threat to homeostasis
3. Signals result in physiologic effects that promote homeostasis.
2. Alert that there is a threat to homeostasis
3. Signals result in physiologic effects that promote homeostasis.
Allostasis
Used to describe the physiologic changes in the neuroendocrine,
autonomic, and immune systems that occur in response to either real or
perceived challenges to homeostasis.
The persistance or accumulation of allostatic changes has been called an
____ _____ and this concept has been used to measure the cumulative effects of
stress on humans.
Allostatic Load
The integration of the response to stress occurs at the ____?
CNS
Give the responsibilities of each:
1. Cerebral Cortex
1. Cerebral Cortex
Responsible for vigilance, cognition, and focused
attention...responsible for running the RAS (Reticular Activating System and
the Lymbic System
2. RAS
Controls mental alertness, ANS activity, and spinal cord refexes which
leads to increased muscle tension
2. Lymbic System
Responsible for emotional responses (fear, anger, rage)
Example: reciprocal connections exist between neurons in the
hypothalamus that intitiate the release of corticotropin releasing factor (CRF)
and neurons in the locus ceruleus associated with the release of norepi. Thus,
norepi stimulates the secreation of CRF, and CRF stimulates the release of
norepi.
...
2. Thalamus
Relay center, important in receiving, sorting, and distributing sensory
input.
3. Locus Ceruleus (LC)
produces norepi (NE) and this thought to be the central integrating site
for the ANS response to stressful stimuli. The LC-NE system has afferent
pathways to the hypothalamus, limbic system, the
hippocampus and the cerebral cortex.
3. Hypothalamus
Coordinates endocrine and autonomic NS response-causes secretion of
CRF-causes secretion of ACTH at anterior pituitary gland-causes secretion of
cortisol at adrenal cortex
When the LC stimulates the ANS, epi and norepi are secreted from the
____ _____?
Adrenal medulla
Give the source of each hormone and its physiological effects:
1. Catecholamines
1. Catecholamines
1. LC, adrenal medulla
2. produces a decrease in insulin release and an increase in glucagon release resulting in increased glycogenolysis, increased heart rate and bp, increased breathing, increased glucose uptake by the periperal tissues...
2. produces a decrease in insulin release and an increase in glucagon release resulting in increased glycogenolysis, increased heart rate and bp, increased breathing, increased glucose uptake by the periperal tissues...
2. CRF or CRH - corticotropin releasing factor
1. Hypothalamus
2. Stumulates ACTH release from the anterior pituitary and increased activity of the LC neurons.
2. Stumulates ACTH release from the anterior pituitary and increased activity of the LC neurons.
3. Adrenocorticotropic
hormone ACTH
1. Anterior Pituitary
2. Stimulates the synthesis and release of cortisol
2. Stimulates the synthesis and release of cortisol
4. Glucocorticoid
Hormones
1. Adrenal Cortex
2. Potentiates the actions of epi and glucagon; alteration in glucose, fat and protein metabolism, suppression of inflammatory and immune responses.
2. Potentiates the actions of epi and glucagon; alteration in glucose, fat and protein metabolism, suppression of inflammatory and immune responses.
Example of glucocorticoid hormone
Cortisol-stress hormone
5. Mineralocorticoid hormones
1. Adrenal cortex
2. Increases Na+ absorption by the kidney
2. Increases Na+ absorption by the kidney
Example of Mineralocorticoid?
Aldosterone
6. Antidiuretic hormone (ADH)
1. Hypothalamus; posterior pituitary
2. Increases water reabsorption by the kidney; produces vasoconstriciton of blood vessels; and stimulates the release of ACTH.
2. Increases water reabsorption by the kidney; produces vasoconstriciton of blood vessels; and stimulates the release of ACTH.
What is another name for ADH
Vasopressin
What are examples of catecholamines?
NE and epi
ANS Sympathetic NS response Process
1. Pain, fear or low B/P signals sent
to hypothalamus
2. Hypothalamus stimulates response from Sympathetic NS
3. SNS neurons signal to the adrenal medulla
4. Adrenal medulla releases NE and epi
5. NE and Epi cause increased heart rate, contractility in heart and vasoconstriction of skin gut and kidney blood vessels
6. These responses automatically increase BP
2. Hypothalamus stimulates response from Sympathetic NS
3. SNS neurons signal to the adrenal medulla
4. Adrenal medulla releases NE and epi
5. NE and Epi cause increased heart rate, contractility in heart and vasoconstriction of skin gut and kidney blood vessels
6. These responses automatically increase BP
Stimulation of the sympathetic nervous system also activates what other
system?
Peripheral renin-angiotensin-aldosterone
system (RAAS)
What is the purpose of the RAAS
Mediates a peripheral increase in
vascular tone and renal retention of sodium and water.
Explain the renin-angiotensin-aldosterone process
Renin enzymatically converts the plasma protein angiotensinogen to
angiotensin I; angiotensin-converting enzyme in the lung converts angiotensi I
to angiotensin II; and angiotensin II produces vasoconstriction and increases
salt and water retention through direct action on the kidney and through
increased aldosterone secretion by the adrenal cortex.
What is the main goal of the renin-angiotensin-aldosterone process?
Control blood pressure
What is the function of ADH
Reabsorption of water.
What is the function of Aldosterone?
Reabsorption of sodium. volume is
added back to the vasculature.
What are some of the functions of Angiotensin II?
Through AT1 receptors in the
hypothalamus and LC, AGII:
1. Enhances CRF formation and release
2. Contributes to the release of ACTH from the pituitary
3. Enhances stress induced release of vasopressin from posterior pituitary
4. Stimulates the release of NE from the LC
1. Enhances CRF formation and release
2. Contributes to the release of ACTH from the pituitary
3. Enhances stress induced release of vasopressin from posterior pituitary
4. Stimulates the release of NE from the LC
Name three other hormones effected by sress?
1. Growth hormone-initially increases,
then decreases
2. Thyroid hormone
3. Reproductive hormone
2. Thyroid hormone
3. Reproductive hormone
Gland where catecholamines are released from?
Adrenal Medulla
In response to acute stress, what substances can result in cool skin and
increase heart rate?
Catecholamines
What clinical manifestation would you expect to observe if ADH is
released?
Decreased urine output
Would a blood glucose level be expected to be higher or lower in
response to cortisol?
Higher
What is the outcome of the RAAS?
Higher BP
Adaptation implies what?
The individual has found balance
between the stressor and the ability to deal with it.
What are the means used to attain this balance called?
Coping Mechanisms/strategies
Name 7 factors affecting the ability to adapt to stress?
1. Physiologic and Anatomic
Reserve-runner
2. Time (long-term bleeding versus immediate hemorrhage)
3. Age, Gender and Genetic Endowment
4. Nutrition and health status
5. Sleep-Wake cycles
6. Hardiness
7. Pshycosocial Factors (support systems-positive and negative)
2. Time (long-term bleeding versus immediate hemorrhage)
3. Age, Gender and Genetic Endowment
4. Nutrition and health status
5. Sleep-Wake cycles
6. Hardiness
7. Pshycosocial Factors (support systems-positive and negative)
The hallmark of the stress response are the ____-____ interactions (ie.
increased corticosteroid production and atrophy of the thymus) that are known
to suppress immunity.
Endocrine-immune
What are the three patterns of stressors?
1. Acute-time limited
2. Chronic intermittent
3. Chronic sustained
2. Chronic intermittent
3. Chronic sustained
What type of stress pattern?
1. Joe lacerates an atery?
1. Joe lacerates an atery?
Acute-time limited
What type of stress pattern?
2. Janice has a middle ear infection five times in the past year?
2. Janice has a middle ear infection five times in the past year?
Chronic intermittent
What type of stress pattern?
3. John has Type I diabetes?
3. John has Type I diabetes?
Chronic sustained
Name 5 nonpharmacologic methods for stress reduction?
1. Relaxation Techniques
2. guided imagery
3. music therapy
4. massage
5. biofeedback
2. guided imagery
3. music therapy
4. massage
5. biofeedback
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