Chapter009

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 9

Stress and Adaptation

Chapter 9

Stress and Adaptation


HomeostasisHomeostasis• The body requires that a level of homeostasis or

constancy be maintained during changes in internal and external environments.

• Give an example in which your body kept some aspect of its internal environment stable. Aspects you might consider include:

– Water balance

– Weight

– Blood glucose

– Temperature


Negative Feedback Control MechanismsNegative Feedback Control Mechanisms


AllostasisAllostasis

• A difference between the perceived situation and desired situation causes the person to take action

• Cognitive activation theory of stress


General Adaptation SyndromeGeneral Adaptation Syndrome

• Also called generalized stress response

– Corticotropin-releasing hormone (CRH) production

– Antidiuretic hormone release

– Sympathetic nervous system (SNS) activation

– Renin-angiotensin-aldosterone pathway activation


stressorschange the internal

environment of part of the body

general adaptation response helps maintain normal function in spite

of the stressor

signs and symptoms

of the change

signs and symptoms of the

general adaptation response


Cortisol—The “Stress Hormone”Cortisol—The “Stress Hormone”

• Helps regulate the stress response

• Diverts metabolism from building tissues to supplying energy for dealing with the stress

• Causes signs and symptoms of chronic stress

CRH

ACTH

Hypothalamus

Anterior pituitary

Adrenal cortex

Cortisol

Alters glucose, fat, and protein

metabolism

Suppresses inflammatory and immune responses


Cortisol ReleaseCortisol Release

• Increases blood glucose

• Stronger sympathetic system effect on heart rate

• Decreases nonessential energy-using activities like:

– Hormone production

º Metabolic rate and reproductive functions decrease

– Bone formation

– Red and white blood cell production

º Immune system becomes depressed


Question Question

Why does cortisol production result in increased blood glucose levels?

a. Glucose leads to a strong sympathetic nervous system response.

b. Glucose stimulates RBC production.

c. Glucose stimulates release of adrenaline.

d. Glucose provides energy.


Answer Answer

d. Glucose provides energy.

The body’s energy requirements increase during periods of stress. Cortisol is the “stress hormone” – one of the effects of cortisol release is increased blood glucose levels. Glucose helps to meet the body’s increased demand for energy.


Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH)

• Also called vasopressin

• Causes vasoconstriction

• Makes kidneys reabsorb water from urine to blood


Sympathetic System—“Fight-or-Flight”Response

Sympathetic System—“Fight-or-Flight”Response

• Rapid response to trauma and emergency

• Epinephrine (adrenalin) and norepinephrine (noradrenalin) both released

• Both attach to adrenergic receptors on cells

hypothalamus

SNS neurons

adrenal medulla

Pain, fear, low BP

SNS activated

Norepinephrine

Epinephrine released into blood


Sympathetic System—“Fight-or-Flight”Response (cont.)

Sympathetic System—“Fight-or-Flight”Response (cont.)• Blood pressure

restored

• Blood flow to skin, guts, and kidneys reduced

• Skin becomes pale

• Urine production decreases

• GI activity decreases

epinephrine and norepinephrine

heart

increased HRincreased heart

strength

increased BP

blood vessels

vasoconstriction in skin, guts,

kidneys


Renin-Angiotensin-Aldosterone PathwayRenin-Angiotensin-Aldosterone Pathway

• Activated by:

– Sympathetic system

– Decreased blood flow to kidneys

• Angiotensin I: weak vasoconstriction

• Angiotensin-converting enzyme (ACE)

• Angiotensin II: stronger vasoconstriction

ACE

Kidneys release renin

Angiotensin I

Angiotensin II


Renin-Angiotensin-Aldosterone Pathway (cont.)Renin-Angiotensin-Aldosterone Pathway (cont.)

• Angiotensin II: stronger vasoconstriction

• Also stimulates the adrenal cortex

• Aldosterone released

adrenal cortex

Angiotensin II

Aldosterone


Question Question

Tell whether the following statement is true or false:

Angiotensin-converting enzyme must be present in order for aldosterone to be released by the adrenal gland.


Answer Answer

True

Without angiotensin-converting enzyme, angiotensin II would not be created. Angiotensin II stimulates the adrenal cortex to produce aldosterone.


Renin-Angiotensin-Aldosterone Pathway

(cont.)

Renin-Angiotensin-Aldosterone Pathway

(cont.)• Aldosterone released

• Na+/K+ ATPase in nephrons activated

– Kidneys reabsorb Na+ and water

– Kidneys secrete K+

kidneys

aldosterone

reabsorb Na+ and water

increased blood volumeoliguria

secrete K+


stressorschange the internal

environment of part of the body

general adaptation response helps maintain normal function in spite

of the stressor

signs and symptoms

of the change

signs and symptoms of the

general adaptation response


Scenario:Scenario:

After an accident, a patient has the following:

• Increased heart rate

• No urine production

• No bowel sounds

• Pale, sweaty skin

• Low blood pressure

• Dilated pupils

• Elevated blood glucose

Question:

• What should be fixed first? Why?


releases

which affect

release

which affect

Central Nervous System

hormones and neurotransmitters

immune cells

inflammatory mediators


Effects of Stress on the Immune SystemEffects of Stress on the Immune System

• Decreased immune cell production

• Decreased thymus activity

• Changes in the kind of immune cells produced


Question Question

How does stress affect your immune system?

a. The thymus atrophies.

b. Fewer lymphocytes are produced.

c. Inflammatory mediators are released.

d. All of the above


Answer Answer

d. All of the above

Stress causes the immune system to be suppressed. The thymus gland atrophies (shrinks), so that fewer T-lymphocytes are produced. Monocytes and lymphocytes cross the blood-brain barrier and release inflammatory mediators and cytokines.


Physiologic StressPhysiologic Stress

• Stress-induced changes in body functions

• Detected by body’s normal regulatory sensors

• The body alters function to restore normal balance

• When normal balance is restored, negative feedback stops the reaction


Psychosocial StressPsychosocial Stress

• Directly affects the central nervous system

• Turns on the stress responses, even when the body’s internal sensors have not detected an imbalance

Question:

• Do the stress responses solve the person’s problem?

• Will negative feedback tell them when to turn off?


Acute StressAcute Stress

Question:

• Which organs of the body would you expect to see damaged by acute stress? Why?


Results of Long-Term StressResults of Long-Term Stress

• Chronic stress

– Sympathetic activity and cortisol are elevated

– Complications result from the reduced immune response

• Posttraumatic stress disorder

– Sympathetic system is activated

– Cortisol levels are decreased


Scenario:Scenario:

Mr. P saw violent combat in the army but he dealt with it and has become a successful air traffic controller.

• He is 50 and overweight:– With increased blood pressure and occasional

tachycardia– Insomnia– GI discomfort– He has had several colds already this year, and

wants a flu shotQuestion:What about his case might be stress-related?


Scenario (cont.):Scenario (cont.):

The doctor has recommended relaxation therapy

• Mr. P is furious about this “new age gobbledygook”

Question:

• How will you explain its physiologic basis to him?

Chapter009

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angiotensin iiwould

aldosterone pathwaycont

orderfor aldosterone

cortisolthe stress hormone

water kidneys

sympathetic systemfight

increased blood glucoselevels