What Is Stress?
Stress is the body's physical and psychological response to situations that are challenging, threatening, or demanding.
Stress can be caused by:
- Exams
- Work
- Money worries
- Family problems
- Illness
- Accidents
- Major life changes
A small amount of stress can help us stay alert and perform well, but long-term stress can affect both physical and mental health.
What Happens When You Feel Stressed?
When your brain detects a threat, it activates two main stress-response systems:
- The Sympathetic-Adrenal-Medullary (SAM) System – the fast response.
- The Hypothalamic-Pituitary-Adrenal (HPA) Axis – the slower, longer-lasting response.
1. The SAM System (Fight-or-Flight)
The SAM system reacts within seconds.
It prepares your body to deal with immediate danger by activating the fight-or-flight response.
During this response:
- ❤️ Heart rate increases.
- 🫁 Breathing becomes faster.
- 👁 Pupils widen.
- 💪 Muscles receive more blood.
- 🍬 Blood sugar rises to provide energy.
- 🍽 Digestion slows down.
The adrenal glands release:
- Adrenaline (epinephrine)
- Noradrenaline (norepinephrine)
These hormones help your body respond quickly to danger.
2. The HPA Axis (Long-Term Stress)
If the stressful situation continues, the HPA axis becomes active.
The process follows these steps:
- 🧠 The hypothalamus releases CRH (Corticotropin-Releasing Hormone).
- 🧠 The pituitary gland releases ACTH (Adrenocorticotropic Hormone).
- 🔺 The adrenal glands release cortisol.
Cortisol is the body's main long-term stress hormone.
What Does Cortisol Do?
Cortisol helps your body cope with prolonged stress by:
- Providing extra energy.
- Increasing blood sugar.
- Maintaining blood pressure.
- Reducing inflammation.
- Temporarily suppressing immune responses.
- Helping you stay alert and focused.
Negative Feedback
Once enough cortisol has been released:
- The hypothalamus reduces CRH production.
- The pituitary gland reduces ACTH production.
- Cortisol levels gradually return to normal.
This is called negative feedback, and it helps restore homeostasis (the body's stable internal balance).
Fight-or-Flight vs. Long-Term Stress
| SAM System | HPA Axis |
|---|---|
| Acts within seconds | Acts over minutes to hours |
| Releases adrenaline and noradrenaline | Releases cortisol |
| Prepares for immediate danger | Helps the body cope with ongoing stress |
| Short-term response | Long-term response |
General Adaptation Syndrome (GAS)
Hans Selye described three stages of stress:
1. Alarm Stage
- Stress is detected.
- The SAM system is activated.
- Adrenaline is released.
- Fight-or-flight begins.
2. Resistance Stage
- The stress continues.
- The HPA axis releases cortisol.
- The body adapts and keeps functioning.
3. Exhaustion Stage
If stress lasts too long:
- Energy reserves become depleted.
- The immune system weakens.
- Fatigue and illness become more likely.
- Burnout can occur.
Long-Term Effects of Chronic Stress
If stress continues for weeks or months, it can increase the risk of:
- 😴 Fatigue
- 😟 Anxiety
- 😞 Depression
- 💤 Sleep problems
- ❤️ High blood pressure
- ❤️ Heart disease
- 🩺 Type 2 diabetes
- ⚖️ Weight gain
- 🤒 Weakened immune system
- 🧠 Memory and concentration problems
Everyday Example
Imagine you are walking home and suddenly hear a loud crash.
Immediate Response
- Your brain detects danger.
- The SAM system releases adrenaline.
- Your heart races.
- You become more alert.
Ongoing Stress
If you later continue worrying about the event:
- The HPA axis becomes active.
- Cortisol is released.
- Your body stays prepared until the situation feels safe again.
Key Terms
Stress
- The body's response to challenges or threats.
SAM System
- The fast stress-response system responsible for the fight-or-flight reaction.
HPA Axis
- The body's long-term hormonal stress-response system.
Adrenaline
- A hormone that prepares the body for immediate action.
Noradrenaline
- A hormone that helps maintain alertness and increases blood pressure during stress.
CRH
- Hormone released by the hypothalamus to begin the HPA response.
ACTH
- Hormone released by the pituitary gland that stimulates the adrenal glands.
Cortisol
- The body's primary hormone for managing prolonged stress.
Homeostasis
- The body's ability to maintain a stable internal environment.
Negative Feedback
- A process that reduces hormone production once cortisol levels are sufficient.
Quick Summary
- Stress activates two main biological systems:
- SAM system (fast response)
- HPA axis (long-term response)
- The SAM system releases adrenaline for immediate action.
- The HPA axis releases cortisol to help the body cope with ongoing stress.
- Once the stress ends, negative feedback reduces cortisol production and restores balance.
- Chronic stress can negatively affect physical and mental health.
Practice Questions
1. Which stress-response system reacts first?
A. HPA axis
B. Immune system
C. SAM system
D. Digestive system
✅ Answer: C
2. Which hormone is mainly responsible for the body's long-term stress response?
A. Insulin
B. Dopamine
C. Adrenaline
D. Cortisol
✅ Answer: D
3. Which hormone is released by the hypothalamus to begin the HPA response?
A. ACTH
B. Cortisol
C. CRH
D. Thyroxine
✅ Answer: C
4. Which stage of General Adaptation Syndrome is associated with burnout and depleted energy?
A. Alarm
B. Resistance
C. Recovery
D. Exhaustion
✅ Answer: D
Easy Memory Tips
SAM = Seconds
- S = Seconds
- A = Adrenaline
- M = Move quickly (fight or flight)
HPA = Hours
- H = Hypothalamus → CRH
- P = Pituitary → ACTH
- A = Adrenal glands → Cortisol
GAS Stages
A → R → E
- Alarm = Immediate danger
- Resistance = Keep coping
- Exhaustion = Burnout if stress continues
These three systems—SAM, HPA, and General Adaptation Syndrome (GAS)—work together to explain how the body responds to both short-term and long-term stress.
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