The HPA axis is activated in response to stress. The hypothalamus secretes CRH, which travels through the portal blood vessels to the anterior pituitary. Here, CRH stimulates corticotrophs to release ACTH into the bloodstream. ACTH then travels to the adrenal cortex, prompting the release of cortisol. Cortisol exerts various physiological effects, including increasing blood sugar levels and suppressing the immune system.
