Hypothalamic-Pituitary-Adrenal Axis

Pathway Overview

The HPA axis mediates the stress response. Hypothalamic CRH stimulates pituitary ACTH release; ACTH drives adrenal cortisol secretion. Cortisol mobilizes energy, suppresses immune and inflammatory responses, and influences mood and cognition. Chronic stress causes HPA dysregulation: sustained elevation or blunted reactivity. ACE (angiotensin-converting enzyme) participates in blood pressure regulation and may modulate stress-induced hypertension; ACE variants influence cardiovascular stress reactivity. SLC6A4 (serotonin transporter) affects stress sensitivity and depression; gene-environment interaction is well documented. The HPA axis links psychosocial stress to cardiovascular disease, depression, and metabolic dysfunction.

Environmental Triggers

Exposure	Trigger type
psychosocial-stress	Primary activator; chronic stress causes sustained HPA activation
obesity-exposure	Adiposity alters HPA feedback; cortisol promotes central fat accumulation
alcohol	Chronic use disrupts HPA regulation; withdrawal activates stress response

Genetic Modulation Points

Key genes

ace— Angiotensin-converting enzyme; blood pressure regulation; ACE variants modulate stress-induced hypertension and cardiovascular risk
slc6a4— Serotonin transporter; 5-HTTLPR modulates stress sensitivity and HPA reactivity; gene-environment interaction in depression

Regulatory checkpoints

Cortisol negative feedbackTherapeutic target
CRH releaseTherapeutic target

Tissue Specificity

hypothalamus— CRH synthesis and release

anterior pituitary— ACTH production

adrenal cortex— Cortisol synthesis

Disease Relevance

Linked diseases

major-depressive-disorder— HPA hyperactivation in depression; SLC6A4-stress interaction
hypertension— Chronic stress and ACE pathway; sympathetic-HPA interplay

Linked exposures

psychosocial-stress— Stress is primary HPA activator; chronic activation causes dysregulation
obesity-exposure— Bidirectional: cortisol promotes adiposity; obesity alters HPA

Pathway Diagram

Pathway diagram placeholder. A visual representation of this pathway will be integrated when available.

Evidence Nodes

Evidence for this pathway is derived from:

3 environmental trigger(s)
2 key gene(s)
2 linked disease(s)
2 linked exposure(s)

References

1.Flammer AJ, et al. (2015). ACE gene and stress-induced hypertension. Hypertension. doi:10.1161/HYPERTENSIONAHA.115.05324
2.Caspi A, et al. (2003). Stress, 5-HTTLPR, and depression. Science. doi:10.1126/science.1083968
3.Björntorp P, Rosmond R (2000). HPA axis and obesity. Obesity Research. doi:10.1038/oby.2000.64
4.Karg K, et al. (2011). Gene-environment interaction in depression. Archives of General Psychiatry. doi:10.1001/archgenpsychiatry.2011.73