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STRESS AND THE BODY

The Core Stress Response

Definition of Stress

Stress refers to the body's response to any demand or threat, real or perceived. The physiological basis of stress involves complex brain-body interactions designed to help an individual respond effectively to challenges. The main physiological models explaining this response include the General Adaptation Syndrome (GAS), the Hypothalamic Pituitary Adrenal (HPA) system, and the Sympathomedullary Pathway (SAM).

Main Physiological Models

1

General Adaptation Syndrome (GAS)

Hans Selye's three-stage process for prolonged stress.
2

HPA Axis

The neuroendocrine system regulating longer-term stress via cortisol.
3

Sympathomedullary Pathway (SAM)

Mediates the immediate, short-term fight-or-flight response.

Key Terminology

Central to these mechanisms is the role of cortisol, a glucocorticoid hormone critical to the stress response.

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Cortisol

Glucocorticoid hormone critical to the stress response.
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Alarm Reaction

Immediate reaction to stress; the fight-or-flight response.
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Resistance

Body attempts to adapt; cortisol remains elevated.
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Exhaustion

Resources depleted; defenses collapse.

HPA Axis (The Longer-Term Pathway)

Hypothalamus (CRH) → Pituitary (ACTH) → Adrenal Cortex (Cortisol)
The HPA axis is a crucial neuroendocrine system responsible for regulating the longer-term stress response.

SAM vs. HPA Timing

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How does the SAM pathway differ from HPA?
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SAM mediates the immediate response within seconds via adrenaline, while HPA mediates the slower, longer-term management of stress via cortisol.

General Adaptation Syndrome (GAS) Stages

Stage Function Description
Alarm Reaction Identify threat, mobilize energy stores Adrenaline/Noradrenaline released
Resistance Adapt to stressor, functions suppressed (digestion, growth) Cortisol remains high
Exhaustion Resources depleted, susceptibility to illness Chronic stress damage

Hormone Effects: Acute Benefits vs. Chronic Risks

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Adrenaline (SAM Pathway)Increases heart rate, blood pressure, and respiration rate. Redirects blood flow to essential muscles, enabling a rapid physical response.
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Cortisol (HPA Pathway)Chronic elevations contribute to immunosuppression and increased risk of diseases such as hypertension. Can impair memory and cognitive processes.

Key Hormone Effects Summary

Detailed physiological actions mediated by the primary stress hormones.

Hormone Pathway Timing Function 1 Function 2 Chronic Issue
Adrenaline SAM Seconds ↑ Heart Rate Dilate Pupils Cardiovascular Strain
Cortisol HPA Slower ↑ Glucose Suppress Immune Hippocampus Damage
Noradrenaline SAM Seconds ↑ Blood Pressure Blood Redirection Prolonged Activation
ACTH HPA Minutes Stimulates Adrenal N/A N/A
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Stress and GAS Deck
Term
Stress

What is stress?

Answer
Definition

The body's response to any demand or threat, real or perceived.

Term
General Adaptation Syndrome (GAS)

Who proposed the General Adaptation Syndrome (GAS)?

Answer
Person

Hans Selye.

Term
Stages of GAS

What are the three stages of GAS?

Answer
Stages

Alarm Reaction, Resistance, Exhaustion.

Term
Alarm Reaction Stage

What happens during the Alarm Reaction stage?

Answer
Explanation

Immediate fight-or-flight response; adrenaline and noradrenaline are released.

Term
Cortisol Role

What is the role of cortisol in stress?

Answer
Role

It regulates metabolism, suppresses non-essential functions, and supports prolonged stress response.

Term
HPA Axis

What does the HPA axis stand for?

Answer
Definition

Hypothalamic Pituitary Adrenal axis.

Term
HPA Axis Hormones

What hormones are involved in the HPA axis stress response?

Answer
Hormones

CRH, ACTH, and cortisol.

Term
SAM Pathway

What does the SAM pathway do?

Answer
Function

Mediates immediate, short-term stress response via adrenaline and noradrenaline release.

Term
Chronic Stress Effects

How can chronic stress affect the body?

Answer
Effects

It can deplete resources, suppress immunity, damage organs, and impair cognitive function.

Term
SAM vs HPA

What is the difference between the SAM and HPA responses?

Answer
Difference

SAM is rapid and short-term; HPA is slower and manages prolonged stress.

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🧠 General Adaptation Syndrome Quiz

1. Who developed the General Adaptation Syndrome model?

Hans Selye proposed GAS in 1936 to explain the stages of physiological stress response.

2. Which hormone is primarily involved in the body’s longer-term stress response?

Cortisol is released via the HPA axis and manages prolonged stress effects.

3. During which stage of GAS does the body attempt to adapt to stress?

Resistance is the stage when the body tries to maintain homeostasis despite ongoing stress.

4. The immediate fight-or-flight response is mediated by which pathway?

The SAM pathway triggers rapid release of adrenaline and noradrenaline.

5. Excessive cortisol due to chronic stress can cause:

High cortisol impairs hippocampal function, leading to cognitive deficits.

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