STRESS

What is stress?

Physical stressors

• Illness• Surgery• Cold• Heat• Hunger• Competitive athletics• Fighting• Fleeing

Psychological stressors

• Any new experience (potentially)• Anticipation of something previously experienced as unpleasant• Situations in which rules are changed or previous behavior no longer effective• Fighting or observing others fighting• Crowding• Acute situations: airplane flight, exam, new situations, competitive athletics, workdays vs weekends• Chronic life situations (divorce, death in the family, illness in the family)

Note: Context matters

Fight or run away?

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Dominance versus submission

Stress and performance in competitive sports

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Physiological responses to stress

• Increased rate and contractility of the heart

• Alterations in blood flow distribution

• Increased gluconeogenesis (synthesis of glucose)

• Mobilization of amino acids (used to synthesize glucose)

• Increased muscle contractility and decreased fatiguability

• Increased learning and memory

Stress

Hypothalamus

Sympathetic nervous system CRH

Epinephrine/norepinephrine ACTH

cortisol

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Location of adrenal glands

Effects of epinephrine

• Increased heart rate and contractility• Effects on arteriolar smooth muscle• Widens pupil and flattens lens (far vision)• Decreases GI motility• Promotes glucose synthesis• Increases central nervous system activity• Decreases fatigue of skeletal muscle

Context matters

Psychological stress: exams

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The Limbic System

Site where emotional stimuli, is integrated, and behavioral and physiologic responses are initiated

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Diurnal variations in plasma cortisol

http://junior.britannica.com/eb/art/print?id=1588&articleTypeId=1

growth ofadrenal cortex

Hans Selye: General Adaptation Response

Chronic exposure of rats to noxious stimuli (cold, restraint, surgery):

• Enlarged adrenal glands• Atrophy of lymphoid structures• Gastric ulcers and bleeding

Note: similar responses were observed with many diversestimuli, including psychological stress

Effects of cortisol

• Increased plasma glucose • Increased contractility of skeletal and cardiac muscle• Inhibits bone growth• Inhibits protein synthesis, accelerates protein degradation

-inhibits collagen formation, easy bruising• Required for maintenance of blood pressure• CNS effects on learning and other responses• Increases gastric secretions• Modulates inflammatory and immune responses

Hans Selye: General Adaptation Response

Chronic exposure of rats to noxious stimuli (cold, restraint, surgery):

• Enlarged adrenal glands• Atrophy of lymphoid structures• Gastric ulcers and bleeding

Note: similar responses were observed with many diversestimuli, including psychological stress

Some conditions in which corticosteroids are useful

• Allergic disorders (asthma, atopic dermatitis)

• Gastrointestinal disorders (Crohn’s disease, ulcerative colitis)

• Arthritis

• Skin irritations

Typical course of prednisone treatment (oral corticosteroid)

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Why is it necessary to “taper off”

Day 6Day 5Day 4Day 3Day 2Day 1

growth ofadrenal cortex

Differences between physical and psychological stressors

Effects of chronic stress

GI system: worsens ulcers

Immune system: immunosuppression (increased autoimmune diseases, increased infections)

Endocrine system: type II diabetes

Growth: retards growth in children, induces weight and bone loss in adults

Cardiovascular system: HypertensionAtherosclerosisSudden cardiac death

From: Cohen SC et al, New England Journal of Medicine 325:606-612, 1991

Psychological stress increases susceptibility to the common cold

Effects of chronic stress

GI system: worsens ulcers

Immune system: immunosuppression (increased autoimmune diseases, increased infections)

Endocrine system: type II diabetes

Growth: retards growth in children, induces weight and bone loss in adults

Cardiovascular system: HypertensionAtherosclerosisSudden cardiac death

From: Mooy J et al, Diabetes Care, 23:1443, 2005

Stress promotes type II diabetes

Effects of chronic stress

GI system: worsens ulcers

Immune system: immunosuppression (increased autoimmune diseases, increased infections)

Endocrine system: type II diabetes

Growth: retards growth in children, induces weight and bone loss in adults

Cardiovascular system: HypertensionAtherosclerosisSudden cardiac death

Leor, J. et al. N Engl J Med 1996;334:413-419

Daily numbers of Deaths Listed by the Department of Coroner of Los Angeles County from January 10 through 23, 1991, 1992, 1993, and 1994

Emotional stress can trigger cardiac events in at risk individuals: Earthquake occurred early in the morning of Jan 17, 1994 in Los Angeles

From: BMJ 2001;323:1443-1446

The number “4” and the word“death” are pronounced similarly in Chinese and Japanese and “4”is considered to be unlucky

US National Mortality Data from 1973 to 1998

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Weighing risk versus reward while experiencing a stressor

Balloon analogue risk task

the image at: psycnet.apa.org/index.cfm?fa=fulltext.printAr...

Lighthall N, et al PLoS One, Volume 4, issue 7, 2009

Males

Stress → testosterone

Females

Stress → oxytocin

Block oxytocin receptors in the brain

Stress

­ heart rate­ cortisol

Stress

­ heart rate­ cortisol

Control treatment

Conclusion: Oxytocin reduces the cardiovascular responses to stress

Wysol, A et al, J Physiol Pharmacol, 59(Suppl 5):117-132, 2008