Health psychology (option): the HPA axis and cortisol

Two stress pathways

When a stressor is perceived, the body responds through two systems:

• The fast SAM pathway (sympathetic-adreno-medullary): the sympathetic nervous system stimulates the adrenal medulla to release adrenaline and noradrenaline: heart rate and blood pressure rise, glucose is released, blood goes to muscles. This is the immediate fight-or-flight response.
• The slower HPA axis, which sustains the response when stress continues.

The HPA axis step by step

1. Hypothalamus releases CRH (corticotropin-releasing hormone).

2. CRH travels to the anterior pituitary gland, which releases ACTH (adrenocorticotropic hormone) into the bloodstream.

3. ACTH reaches the adrenal cortex (outer layer of the adrenal glands), which releases glucocorticoids, mainly cortisol.

4. Negative feedback: cortisol acts on receptors in the hypothalamus and pituitary (and hippocampus), which reduce CRH and ACTH, switching the response off when the threat has passed.

Cortisol: the stress hormone

Short-term benefits: raises blood glucose (by converting protein and mobilising fat) for energy; reduces inflammation; suppresses non-essential functions such as digestion and reproduction.

Long-term costs when stress is chronic and cortisol stays high: immune suppression (more infections, slower healing), raised blood pressure and cardiovascular problems, digestive problems, and effects on the brain (see the next lesson).

Measuring stress: cortisol can be measured in saliva, blood or urine, giving an objective biological measure (used in the MindUP study, Schonert-Reichl et al., 2015).

Evaluation

• Strengths: strong biological evidence; cortisol measurement gives objective, quantitative data; explains links between chronic stress and illness.
• Weaknesses: reductionist: it ignores how people appraise stressors (Lazarus) and individual differences; cortisol varies over the day (highest in the morning), so measurements must be timed carefully (reliability); much early evidence comes from animal research (Selye's rats), raising generalisability questions.

Worked example

A student faces a week of exams. Describe the role of the HPA axis.

1. The hypothalamus perceives the ongoing stressor and releases CRH.
2. CRH causes the anterior pituitary to release ACTH into the blood.
3. ACTH causes the adrenal cortex to release cortisol, raising blood glucose for energy.
4. If stress continues all week, cortisol stays high and may suppress the immune system.

Answer: Hypothalamus (CRH), pituitary (ACTH), adrenal cortex (cortisol), with negative feedback.

Check yourself

1. Which hormone does the hypothalamus release at the start of the HPA axis?
   • ACTH
   • Cortisol
   • CRH
   • Adrenaline
   Show answer

   CRH. Corticotropin-releasing hormone.

2. ACTH is released by the
   • anterior pituitary gland
   • adrenal cortex
   • hypothalamus
   • adrenal medulla
   Show answer

   anterior pituitary gland. The pituitary releases ACTH.

3. Cortisol is released from the
   • adrenal medulla
   • hippocampus
   • adrenal cortex
   • pituitary gland
   Show answer

   adrenal cortex. The outer layer of the adrenal glands.

4. Which hormone is released in the fast SAM pathway?
   • Cortisol
   • Adrenaline
   • CRH
   • ACTH
   Show answer

   Adrenaline. The adrenal medulla releases adrenaline.

5. What is the role of negative feedback in the HPA axis?
   • It increases cortisol release without limit
   • It starts the SAM pathway
   • It releases adrenaline
   • High cortisol reduces CRH and ACTH release, switching the response off
   Show answer

   High cortisol reduces CRH and ACTH release, switching the response off. Cortisol shuts down its own production.

6. Why can chronic stress lead to more infections?
   • Cortisol kills viruses
   • Prolonged high cortisol suppresses the immune system
   • ACTH damages the skin
   • Adrenaline lowers blood glucose
   Show answer

   Prolonged high cortisol suppresses the immune system. Immune suppression.

7. Describe the HPA axis response to stress.
   Show answer

   The hypothalamus releases CRH, which makes the pituitary gland release ACTH into the blood; ACTH makes the adrenal cortex release cortisol, which raises blood sugar, and negative feedback switches the system off.. Three structures and their hormones.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification, Issue 6 (November 2024, first assessment January 2026)
• OpenStax Psychology: 14.1 What is stress? (HPA axis, cortisol, general adaptation syndrome)
• Schonert-Reichl, Oberle, Lawlor and others (2015), Enhancing cognitive and social-emotional development through a simple-to-administer mindfulness-based school program, Developmental Psychology 51(1)

Last updated 8 November 2026. Spotted a mistake? Tell us.