Stress Physiology
Stress is the body’s nonspecific response to any demand placed upon it. The stress response involves a complex interplay of neural, endocrine, and immune systems designed to maintain homeostasis in the face of challenges.
The General Adaptation Syndrome
Hans Selye’s General Adaptation Syndrome (GAS) describes three stages of the stress response:
| Stage | Duration | Characteristics | Physiology |
|---|---|---|---|
| Alarm | Immediate (minutes-hours) | Fight-or-flight activation | Sympathetic nervous system activation; HPA axis triggered |
| Resistance | Days-weeks | Adaptation and coping | Cortisol elevation maintained; energy mobilized |
| Exhaustion | Prolonged stress | System breakdown | Depletion of resources; increased vulnerability to disease |
The HPA Axis
The hypothalamic-pituitary-adrenal (HPA) axis is the body’s central stress response system.
Activation pathway:
Stressor
↓
Hypothalamus (paraventricular nucleus)
↓ releases
Corticotropin-releasing hormone (CRH)
↓ via hypophyseal portal system
Anterior pituitary
↓ releases
Adrenocorticotropic hormone (ACTH)
↓ via bloodstream
Adrenal cortex
↓ releases
Cortisol (glucocorticoid)
Negative feedback: Cortisol acts back on the hypothalamus and pituitary to suppress further CRH and ACTH release, creating a regulatory feedback loop.
Cortisol
Cortisol is the primary stress hormone in humans, with wide-ranging effects throughout the body.
| System | Effects of Cortisol |
|---|---|
| Metabolism | Increases blood glucose (gluconeogenesis); protein catabolism; lipolysis |
| Immune | Anti-inflammatory (initially); suppresses immune function with chronic elevation |
| Cardiovascular | Enhances vascular tone; permissive for catecholamine effects |
| Central nervous | Alters neurotransmitter activity; affects memory consolidation |
| Bone | Decreases bone formation; increases bone resorption |
| Growth | Suppresses growth hormone and IGF-1 |
Normal cortisol physiology:
- Diurnal rhythm: Highest ~30 minutes after waking, lowest at midnight
- Pattern: Cortisol awakening response (CAR) + declining curve through the day
- Disruption: Chronic stress, shift work, sleep deprivation alter diurnal pattern
Sympathetic-Adrenal-Medullary (SAM) System
The SAM system mediates the rapid “fight-or-flight” response:
Stressor
↓
Hypothalamus → Sympathetic nervous system
↓
Adrenal medulla
↓ releases
Epinephrine (80%) and Norepinephrine (20%)
Acute effects:
- Increased heart rate, contractility, and blood pressure
- Bronchodilation
- Pupil dilation
- Redistribution of blood flow (away from non-essential organs)
- Increased blood glucose
- Enhanced coagulation
- Sweating
Acute vs. Chronic Stress
Acute Stress
| Feature | Description |
|---|---|
| Duration | Minutes to hours |
| Trigger | Immediate threat or challenge |
| Physiology | Sympathetic activation; rapid hormonal response |
| Cognitive effects | Enhanced focus, alertness, memory consolidation |
| Recovery | Usually complete after threat passes |
| Health effects | Generally adaptive; may enhance immune function |
Chronic Stress
| Feature | Description |
|---|---|
| Duration | Weeks to years |
| Trigger | Ongoing demands (work, finances, caregiving, discrimination) |
| Physiology | Persistent HPA activation; altered cortisol rhythm |
| Cognitive effects | Impaired concentration, memory deficits, executive dysfunction |
| Recovery | Incomplete; allostatic load accumulates |
| Health effects | Maladaptive; contributes to disease |
Allostasis and Allostatic Load
- Allostasis: The process of achieving stability through physiological change (adaptation)
- Allostatic load: The cumulative physiological cost of repeated or chronic stress adaptation
Primary mediators of allostatic load:
| Mediator | Chronic Elevation | Chronic Suppression |
|---|---|---|
| Cortisol | Metabolic syndrome, immune suppression, hippocampal atrophy | Autoimmune activation, inflammation |
| Catecholamines | Hypertension, cardiovascular damage | Fatigue, hypotension |
| Inflammatory cytokines | Depression, cardiovascular disease | Infection risk |
Types of allostatic overload:
- Repeated hits: Multiple acute stressors
- Lack of adaptation: Failure to habituate to repeated stressor
- Prolonged response: Stressor continues, response fails to terminate
- Inadequate response: Insufficient response leads to compensatory hyperactivity of other mediators
Health Consequences of Chronic Stress
| System | Conditions |
|---|---|
| Cardiovascular | Hypertension, coronary artery disease, stroke, arrhythmias |
| Metabolic | Obesity, type 2 diabetes, metabolic syndrome |
| Immune | Increased infection susceptibility, autoimmune flares, slower wound healing |
| Gastrointestinal | IBS, GERD, ulcers (H. pylori interaction) |
| Neurological | Cognitive decline, hippocampal atrophy, increased dementia risk |
| Mental health | Depression, anxiety, burnout, PTSD, substance use |
| Reproductive | Menstrual irregularities, erectile dysfunction, reduced libido |
| Musculoskeletal | Chronic pain, tension headaches, TMJ disorders |
Coping Mechanisms
Coping refers to the cognitive and behavioral efforts to manage internal and external demands that are appraised as exceeding available resources.
The Transactional Model of Stress and Coping
Lazarus and Folkman’s model emphasizes the role of cognitive appraisal:
Primary appraisal: Is this event relevant to my well-being? Is it a threat, challenge, harm/loss, or benign?
Secondary appraisal: Do I have the resources to cope with this demand?
Reappraisal: Continuous updating based on new information and outcomes
Coping Styles
| Dimension | Description | Examples |
|---|---|---|
| Problem-focused vs. Emotion-focused | Address stressor directly vs. manage emotional response | Problem: making a plan, seeking information; Emotion: meditation, venting |
| Approach vs. Avoidance | Active engagement with stressor vs. efforts to avoid it | Approach: problem-solving; Avoidance: denial, substance use |
| Cognitive vs. Behavioral | Changing thinking vs. changing actions | Cognitive: reframing; Behavioral: exercising |
| Proactive vs. Reactive | Anticipating/preventing vs. responding to stressor | Proactive: planning; Reactive: crisis management |
Adaptive (Approach-Oriented) Coping Strategies
| Strategy | Description | Evidence |
|---|---|---|
| Problem-solving | Systematic approach to identify solutions, steps, and implement them | Strong: improves outcomes across stressors |
| Cognitive reappraisal | Changing the meaning of a stressor to reduce its threat | Strong: key mechanism in CBT |
| Emotional regulation | Identifying, accepting, and managing emotions | Strong: core of DBT, ACT |
| Social support | Seeking tangible, informational, or emotional support | Strong: buffer against stress effects |
| Mindfulness | Non-judgmental awareness of present moment | Strong: reduces stress, improves well-being |
| Acceptance | Acknowledging reality without fighting it | Strong: central to ACT |
| Humor | Finding comedy or lightness in difficult situations | Moderate: reduces distress |
| Meaning-making | Finding purpose or growth through adversity | Moderate: post-traumatic growth |
Maladaptive (Avoidance-Oriented) Coping Strategies
| Strategy | Description | Consequences |
|---|---|---|
| Denial | Refusing to acknowledge stressor | Delays coping; stressor often worsens |
| Behavioral disengagement | Giving up or withdrawing effort | Maintains or worsens problem |
| Substance use | Alcohol, drugs to numb or escape | Creates secondary problems; dependence |
| Self-blame | Excessive self-criticism | Increases distress; reduces self-efficacy |
| Rumination | Repetitive, passive focus on distress and its causes | Maintains depression, anxiety |
| Catastrophizing | Imagining worst-case scenarios | Increases anxiety; impairs problem-solving |
| Expressive suppression | Hiding emotional expression | Paradoxically increases arousal; impairs cognition |
| Avoidance | Evading situations, thoughts, feelings | Reinforces fear; prevents learning |
Cortical vs. Limbic Dominance
The “low road” (limbic) and “high road” (cortical) pathways:
- Low road: Sensory input → thalamus → amygdala → immediate threat response (fast but inaccurate)
- High road: Sensory input → thalamus → sensory cortex → prefrontal cortex → amygdala → modulated response (slower but accurate)
Stress Management Techniques
Relaxation Techniques
| Technique | Description | Evidence Base |
|---|---|---|
| Progressive muscle relaxation (PMR) | Systematic tensing and relaxing of muscle groups | Strong: anxiety, insomnia, pain |
| Diaphragmatic breathing | Slow, deep belly breathing (4-7-8 patterns) | Strong: autonomic regulation |
| Autogenic training | Self-suggestion of warmth and heaviness | Moderate: tension, anxiety |
| Guided imagery | Visualizing calming scenes or healing processes | Moderate: pain, anxiety |
| Body scan | Systematic attention through body regions | Strong: mindfulness-based interventions |
Mindfulness and Meditation
Mindfulness-Based Stress Reduction (MBSR):
- Developed by Jon Kabat-Zinn
- 8-week program: weekly sessions + daily home practice
- Core practices: body scan, sitting meditation, walking meditation, yoga
- Strong evidence: stress reduction, anxiety, depression, pain, burnout
Mindfulness-Based Cognitive Therapy (MBCT):
- Adapted from MBSR for depression relapse prevention
- Combines mindfulness with CBT techniques
- Strong evidence: depression relapse prevention, especially in those with 3+ episodes
Transcendental Meditation (TM):
- Mantra-based meditation (20 minutes, twice daily)
- Moderate evidence: blood pressure reduction, anxiety
Exercise
| Type | Effects | Recommendations |
|---|---|---|
| Aerobic (running, swimming, cycling) | ↓ Cortisol, ↑ Endorphins, ↑ BDNF, ↑ mood | 150 min/week moderate or 75 min/week vigorous |
| Resistance training | ↓ Anxiety, ↑ self-efficacy, ↑ mood | 2-3 sessions/week |
| Yoga | ↓ Cortisol, ↓ Stress, ↓ Anxiety | Minimum 2-3 sessions/week |
| Tai chi/Qigong | ↓ Stress, ↓ Falls risk (elderly) | Regular practice recommended |
Mechanism of exercise benefits:
- Endorphin release
- Endocannabinoid activation
- BDNF upregulation (neuroplasticity)
- Temperature elevation
- Mastery and self-efficacy
- Social engagement
- Distraction from stressors
Sleep and Stress Management
| Relationship | Description |
|---|---|
| Stress → Sleep disruption | HPA activation, hyperarousal impair sleep initiation and maintenance |
| Sleep disruption → stress | Poor sleep impairs emotion regulation, increases next-day stress reactivity |
| Vicious cycle | Stress and sleep problems mutually reinforce each other |
| Intervention | Sleep hygiene improves stress resilience; stress reduction improves sleep |
Time Management and Organizational Strategies
| Technique | Description |
|---|---|
| Prioritization (Eisenhower matrix) | Categorize tasks by urgency and importance |
| Pomodoro technique | 25-minute focused work intervals with breaks |
| ABC method | Rank tasks by priority A (high) → C (low) |
| SMART goals | Specific, Measurable, Achievable, Relevant, Time-bound |
| Boundary setting | Clear limits on work hours, availability, responsibilities |
Social Support
| Type | Description | Example |
|---|---|---|
| Instrumental | Tangible help | Financial assistance, transportation |
| Informational | Advice, guidance | Referral to resources, information |
| Emotional | Comfort, empathy, validation | Listening, reassurance |
| Appraisal | Constructive feedback | Perspective on performance, behavior |
Stress-buffering hypothesis: Social support protects against the negative health effects of stress by: (1) altering appraisal of stressors, (2) reducing physiological reactivity, (3) promoting adaptive coping.
Cognitive Strategies
Cognitive restructuring:
- Identify cognitive distortions:
- All-or-nothing thinking
- Catastrophizing
- Mind reading
- Emotional reasoning
- Overgeneralization
- Generate alternative, balanced thoughts
- Examine evidence for and against automatic thoughts
The ABCDE model (Ellis’s REBT):
- A: Activating event
- B: Beliefs about the event
- C: Consequences (emotional, behavioral)
- D: Disputing irrational beliefs
- E: Effective new response
Biofeedback and Neurofeedback
| Modality | Measures | Application |
|---|---|---|
| Heart rate variability (HRV) biofeedback | Beat-to-beat heart rate variation | Stress reduction, anxiety, hypertension |
| Electromyography (EMG) biofeedback | Muscle tension | Tension headaches, TMJ, chronic pain |
| Thermal biofeedback | Skin temperature | Raynaud’s, migraine, anxiety |
| Neurofeedback (EEG) | Brain wave patterns | ADHD, anxiety, depression |
Resilience Building
Resilience is the ability to adapt positively in the face of adversity. Key factors:
| Factor | Description | How to Build |
|---|---|---|
| Optimism | Expectation of positive outcomes | Cognitive restructuring, gratitude practice |
| Self-efficacy | Belief in ability to succeed | Mastery experiences, vicarious learning |
| Emotional regulation | Ability to manage emotions | Mindfulness, DBT skills |
| Social connectedness | Strong relationships | Nurturing relationships, seeking support |
| Sense of meaning | Purpose and values | Values clarification, goal-setting |
| Adaptability | Flexibility in approach | Growth mindset, exposure to challenges |
Burnout
Burnout is a state of emotional, physical, and mental exhaustion caused by excessive and prolonged stress. It is characterized by:
| Dimension | Description |
|---|---|
| Exhaustion | Feeling drained, depleted, unable to cope |
| Cynicism/depersonalization | Negative, detached attitude toward work/people |
| Reduced professional efficacy | Feelings of incompetence, lack of achievement |
Risk factors:
- High workload, low control
- Lack of recognition
- Poor workplace relationships
- Values conflict
- Emotional demands
- Perfectionism
Interventions:
- Individual: CBT, mindfulness, self-care, boundaries
- Organizational: Workload management, autonomy, recognition, support systems
References
- Selye, H. (1936). A syndrome produced by diverse nocuous agents. Nature, 138(3479), 32.
- McEwen, B. S. (2007). Physiology and neurobiology of stress and adaptation. Physiological Reviews, 87(3), 873-904.
- Lazarus, R. S., & Folkman, S. (1984). Stress, Appraisal, and Coping. Springer.
- Sapolsky, R. M. (2004). Why Zebras Don’t Get Ulcers (3rd ed.). Henry Holt.
- Kabat-Zinn, J. (2003). Mindfulness-based stress reduction. Clinical Psychology: Science and Practice, 10(2), 144-156.
- American Psychological Association. (2023). Stress effects on the body. APA.
- National Institute of Mental Health. (2023). 5 Things You Should Know About Stress. NIMH.
- Cohen, S., et al. (2007). Psychological stress and disease. JAMA, 298(14), 1685-1687.