8.2 Acute vs. chronic stress effects on the body and brain

Stress can be acute or chronic, each affecting our bodies differently. Acute stress triggers the "fight-or-flight" response, releasing hormones that cause temporary changes. Chronic stress, however, keeps our stress response system activated, leading to long-term health issues.

Acute stress can be beneficial, enhancing focus and immune function. But chronic stress disrupts bodily systems, suppressing immunity and impairing memory. It can cause cardiovascular problems, digestive issues, and even change brain structure, impacting our overall well-being.

Acute vs Chronic Stress Effects

Physiological Responses and Duration

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• Acute stress triggers immediate "fight-or-flight" response activating sympathetic nervous system and hypothalamic-pituitary-adrenal (HPA) axis
• Acute stress rapidly releases stress hormones (cortisol, epinephrine, norepinephrine) causing temporary physiological changes (increased heart rate, blood pressure)
• Chronic stress prolongs activation of stress response system sustaining elevated stress hormone levels
• Acute stress resolves quickly allowing body to return to homeostasis
• Chronic stress disrupts homeostatic mechanisms over extended periods (weeks to months)
• Duration and frequency of stressors determine whether stress response becomes chronic and potentially harmful

Adaptive vs Maladaptive Effects

• Acute stress can be adaptive and beneficial enhancing focus and performance (improved reaction time during emergencies)
• Chronic stress leads to dysregulation of various bodily systems increasing health problem risks (cardiovascular disease, depression)
• Acute stress typically improves immune function short-term (increased white blood cell production)
• Chronic stress suppresses immune system making individuals more susceptible to infections and slowing wound healing
• Acute stress can enhance memory formation for important events (remembering details during an accident)
• Chronic stress impairs memory and cognitive function through prolonged elevation of stress hormones

Chronic Stress on Body Systems

Cardiovascular System Effects

• Persistent elevation of blood pressure and heart rate increases hypertension and cardiovascular disease risks
• Prolonged stress causes endothelial dysfunction promoting atherosclerosis (plaque buildup in arteries)
• Increased likelihood of heart attacks and strokes due to chronic stress-induced inflammation and blood vessel damage
• Stress hormones like cortisol and adrenaline can lead to arrhythmias (irregular heartbeats)
• Chronic stress contributes to unhealthy behaviors (poor diet, lack of exercise) further impacting cardiovascular health

Immune System Impacts

• Chronic activation of stress response suppresses immune system increasing susceptibility to infections (common colds, flu)
• Stress-induced immunosuppression contributes to reactivation of latent viruses (herpes simplex, Epstein-Barr)
• Increased risk of autoimmune disorders due to dysregulation of immune responses (rheumatoid arthritis, lupus)
• Prolonged stress alters production and function of various immune cells (T cells, natural killer cells)
• Chronic stress delays wound healing processes by reducing inflammatory response and collagen production

Digestive System Disruptions

• Chronic stress alters gut motility leading to issues like constipation or diarrhea
• Increased inflammation in the digestive tract exacerbates conditions like inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• Disruption of gut microbiome balance contributes to various gastrointestinal problems (bloating, abdominal pain)
• Stress-related digestive issues manifest as irritable bowel syndrome (IBS) and peptic ulcers
• Gut-brain axis mediates effects of chronic stress on digestive system through vagus nerve and neuroendocrine signaling
• Chronic stress can lead to changes in appetite and eating patterns (emotional eating, loss of appetite)

Chronic Stress and Brain Changes

Structural Alterations

• Chronic stress causes atrophy of hippocampus crucial for memory formation and stress regulation
• Prolonged stress exposure leads to dendritic retraction and reduced neurogenesis in hippocampus
• Prefrontal cortex undergoes structural changes including reduced gray matter volume and altered connectivity
• Chronic stress enhances activity and causes hypertrophy in amygdala key for emotional processing and fear responses
• Stress-induced changes in brain's reward system alter dopamine signaling (nucleus accumbens, ventral tegmental area)

Functional and Neurochemical Changes

• Impaired learning and memory processes due to hippocampal atrophy and reduced neuroplasticity
• Altered executive functions (decision-making, impulse control) resulting from prefrontal cortex changes
• Enhanced emotional reactivity and anxiety due to amygdala hypertrophy and hyperactivity
• Disrupted balance between various neurotransmitter systems affecting mood, cognition, and behavior
• Increased vulnerability to addiction and depression through alterations in reward circuitry
• Epigenetic modifications induced by chronic stress lead to long-lasting changes in gene expression affecting brain function across lifespan

Allostatic Load in Chronic Stress

Concept and Mechanisms

• Allostatic load refers to cumulative wear and tear on body's systems due to repeated or chronic stress exposure
• Allostasis underlying body's adaptive responses to stressors maintains stability through change
• Allostatic load encompasses physiological consequences of chronic exposure to fluctuating or heightened neural or neuroendocrine responses
• Primary mediators of allostatic load include stress hormones (cortisol) and inflammatory cytokines
• Secondary outcomes involve metabolic, cardiovascular, and immune parameters reflecting cumulative effects of chronic stress

Assessment and Implications

• Measuring allostatic load through multiple biomarkers provides comprehensive assessment of biological impact of chronic stress
• Biomarkers may include cortisol levels, blood pressure, cholesterol, glycated hemoglobin, and inflammatory markers (C-reactive protein)
• Allostatic load model explains individual differences in stress vulnerability and resilience based on genetic, developmental, and environmental factors
• Higher allostatic load associated with increased risk of various health problems (cardiovascular disease, cognitive decline, depression)
• Interventions targeting allostatic load reduction may include stress management techniques, lifestyle modifications, and social support enhancement