Source: Abnormal Psychology lecture notes (University of Florida)
Tags: stress, stress response, SAM system, HPA axis, cortisol, epinephrine, norepinephrine, fight or flight, allostasis, allostatic load, chronic stress, immune suppression, cardiovascular disease, glucocorticoids, catecholamines, stress management
Difficulty: Intermediate | Prerequisites: Basic understanding of the nervous system and endocrine system.
Stress is where psychology meets physiology. This topic sits at the intersection of abnormal psychology and biological psychology, and it underpins a large portion of the course material on psychopathology, health psychology, and treatment. You need to understand two physiological systems (the SAM system and the HPA axis), what happens when they stay switched on too long, and the downstream consequences for the cardiovascular system, the immune system, and cognition. If you are comfortable with basic anatomy of the brain (hypothalamus, pituitary) and the idea of hormones acting as chemical messengers, you are ready to go.
The body responds to stress through two main pathways: the SAM system (fast, adrenaline-driven) and the HPA axis (slower, cortisol-driven). Short bursts of activation are protective, but chronic activation leads to cardiovascular disease, immune suppression, and cognitive problems. The cumulative wear this causes is called allostatic load, and it can be reduced through exercise and social support.
Sympathetic Adrenal-Medullary (SAM) system
The branch of the stress response that triggers the release of catecholamines (epinephrine and norepinephrine) from the adrenal medulla. Think of it as the body's fast-acting alarm system, the one responsible for the immediate "fight or flight" reaction.
Hypothalamic Pituitary Adrenal (HPA) axis
A slower hormonal cascade running from the hypothalamus to the pituitary gland to the adrenal cortex, ending in cortisol release. In simple terms, this is the body's sustained stress-response system, the one that keeps you alert and fuelled over hours rather than seconds.
Catecholamines
A class of hormones that includes epinephrine (adrenaline) and norepinephrine (noradrenaline). They prepare the body for rapid physical action.
Epinephrine (adrenaline)
A catecholamine released by the adrenal medulla that boosts glucose metabolism, increases blood flow, and raises blood pressure. Think of it as the fuel injector, making stored energy available fast.
Norepinephrine (noradrenaline)
A catecholamine that also acts as a neurotransmitter in the brain, increasing alertness and heart rate during stress. In simple terms, it sharpens your focus and keeps you on edge.
Corticotropin-releasing hormone (CRH)
The hormone the hypothalamus secretes to kick off the HPA axis cascade. It signals the pituitary to release ACTH.
Adrenocorticotropic hormone (ACTH)
Released by the anterior pituitary in response to CRH; it tells the adrenal cortex to produce glucocorticoids, chiefly cortisol.
Glucocorticoids
Steroid hormones (primarily cortisol) released by the adrenal cortex that regulate energy metabolism, immune function, and behavioural responses. Think of them as the body's longer-duration stress fuel, breaking down proteins and fats for energy.
Cortisol
The principal glucocorticoid in humans. It provides sustained energy during stress by breaking down proteins and fats, but chronic elevation suppresses the immune system, impairs cognition, and contributes to cardiovascular disease.
Allostasis
The process by which the body achieves stability through physiological or behavioural change in response to stressors. In simple terms, it is the body constantly recalibrating to cope with demands.
Allostatic load
The cumulative biological cost of repeated or chronic stress. Think of it as wear and tear on the body's stress-response systems from being switched on too often or for too long.
Steroid psychosis
A psychiatric condition caused by long-term glucocorticoid exposure, characterised by distractibility, depression, and hallucinations.
The hypothalamus detects a stressor and activates the sympathetic nervous system.
The sympathetic nervous system stimulates the adrenal medulla (the inner part of the adrenal gland).
The adrenal medulla releases catecholamines: epinephrine and norepinephrine.
Epinephrine effects:
Enhances glucose metabolism, unlocking stored nutrients for immediate energy.
Increases blood flow and blood pressure.
Over the long term, chronic elevation contributes to cardiovascular disease.
Norepinephrine effects:
Functions as both a hormone and a neurotransmitter in the brain.
Increases alertness and heart rate.
Mediates behavioural responses to stress (vigilance, readiness to act).
The hypothalamus secretes corticotropin-releasing hormone (CRH).
CRH travels to the anterior pituitary, which releases adrenocorticotropic hormone (ACTH).
ACTH travels through the bloodstream to the adrenal cortex (the outer layer of the adrenal gland).
The adrenal cortex releases glucocorticoids, primarily cortisol.
Cortisol effects:
Breaks down proteins and fats to provide sustained energy.
Increases blood flow.
Modulates behavioural responses.
Chronic elevation suppresses the immune system and impairs other vital functions.
Cardiovascular disease: Chronic stress is linked to hypertension, heart disease, and stroke. Air traffic controllers in high-stress environments show higher rates of blood pressure problems and related illness.
Cognitive impairment: Long-term glucocorticoid exposure can produce cognitive deficits, anxiety, and steroid psychosis (distractibility, depression, hallucinations).
Immune suppression: Sustained glucocorticoid secretion inhibits immune responses, increases susceptibility to infections, and slows wound healing. Caregivers for Alzheimer's patients, for example, show significantly slower healing of minor wounds than less stressed individuals.
Allostasis is the body's ongoing effort to maintain stability through change.
Allostatic load is what accumulates when that effort never lets up, the biological cost of chronic recalibration.
High allostatic load is the bridge between "I feel stressed" and measurable health damage (cardiovascular, immune, cognitive).
Physical activity: Regular exercise reduces allostatic load by promoting overall physical health and building resilience to stress.
Social integration: Supportive relationships and strong social networks buffer against the negative effects of stress and improve mental and emotional well-being.
Early life experiences: Early life stressors can have lasting effects on brain development and stress reactivity. Positive early experiences and interventions can build resilience and offset some of the adverse effects of chronic stress on mental health.
The SAM/HPA framework explains why people in high-pressure occupations (air traffic controllers, emergency responders, intensive caregivers) develop specific clusters of health problems: hypertension, weakened immunity, cognitive fog. It also explains why "just relaxing" is insufficient advice, because the allostatic load has already accumulated at a physiological level, and recovery requires sustained behavioural change (exercise, social support) rather than a single holiday.
Students often confuse the SAM system with the HPA axis. The SAM system is fast and catecholamine-driven (seconds to minutes). The HPA axis is slower and cortisol-driven (minutes to hours). They are parallel systems, not stages of the same system.
Students sometimes think cortisol is entirely harmful. In the short term, cortisol is protective and adaptive. The damage comes from chronic elevation, not from cortisol itself.
Students may assume "allostasis" and "allostatic load" are interchangeable. Allostasis is the healthy adaptive process. Allostatic load is what happens when that process is overused.
Students sometimes overlook that norepinephrine has a dual role: it is both a hormone (released from the adrenal medulla) and a neurotransmitter (acting in the brain). Exam questions may test this distinction.
⚠️ Be able to trace both pathways from stressor to hormone: hypothalamus → sympathetic nervous system → adrenal medulla → catecholamines (SAM), and hypothalamus → CRH → anterior pituitary → ACTH → adrenal cortex → cortisol (HPA).
⚠️ Know the specific health consequences of chronic stress: cardiovascular disease, immune suppression, cognitive impairment / steroid psychosis.
⚠️ Understand allostatic load as the cumulative burden concept, and be prepared to distinguish it from allostasis.
⚠️ The air traffic controller example and the Alzheimer's caregiver wound-healing study are the kind of concrete examples that appear on exams.
True or false: The SAM system releases cortisol.
False. The SAM system releases catecholamines (epinephrine and norepinephrine). Cortisol is released via the HPA axis.
Fill in the blank: The cumulative biological cost of chronic stress is called ________.
Allostatic load.
True or false: Short-term cortisol release is harmful to the body.
False. Short-term cortisol is adaptive and provides energy. Chronic elevation is what causes damage.
Fill in the blank: CRH is released by the ________, and ACTH is released by the ________.
Hypothalamus; anterior pituitary.
True or false: Norepinephrine functions only as a hormone.
False. It also functions as a neurotransmitter in the brain.
Q: Describe the sequence of events in the HPA axis from initial stressor to cortisol release.
A: The hypothalamus secretes corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH). ACTH travels through the blood to the adrenal cortex, which responds by releasing glucocorticoids, primarily cortisol.
Q: Name three negative health outcomes associated with chronic stress and briefly explain the mechanism for each.
A: (1) Cardiovascular disease, caused by sustained elevation of blood pressure and blood flow from catecholamines and cortisol. (2) Immune suppression, caused by prolonged glucocorticoid secretion inhibiting immune responses. (3) Cognitive impairment, caused by long-term glucocorticoid exposure leading to deficits, anxiety, and potentially steroid psychosis.
Q: What is allostatic load, and how does it differ from allostasis?
A: Allostasis is the body's normal process of achieving stability through physiological change in response to stressors. Allostatic load is the cumulative wear and tear on the body when this adaptive process is chronically activated, leading to health problems.
Q: How does the SAM system differ from the HPA axis in terms of speed, hormones released, and primary effects?
A: The SAM system is fast-acting, releases catecholamines (epinephrine and norepinephrine), and produces immediate fight-or-flight responses (increased heart rate, blood pressure, alertness). The HPA axis is slower, releases glucocorticoids (cortisol), and provides sustained energy by breaking down proteins and fats while modulating immune and behavioural responses.
Q: Identify two evidence-based strategies for reducing allostatic load.
A: Physical activity (exercise reduces allostatic load by promoting overall health and stress resilience) and social integration (supportive relationships buffer against the negative effects of chronic stress).
This material connects directly to psychopathology topics in abnormal psychology: chronic HPA axis activation is implicated in major depressive disorder and anxiety disorders. Understanding immune suppression from chronic stress also links to health psychology and psychoneuroimmunology. The concept of early life stressors shaping later stress reactivity connects to developmental psychology and the study of adverse childhood experiences (ACEs).
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