The HPA axis is one major route by which the hypothalamus can step on the gas pedal and rev the body up. The HPA axis includes the hypothalamus, pituitary gland, and adrenal glands. This triad is centrally involved in the stress response of the body. The pituitary gland is a small structure below the hypothalamus and the adrenal glands lie just above the kidneys. The hypothalamus secretes a hormone known as cortisol releasing hormone (CRH), which travels down to the pituitary gland, where it stimulates the release of adrenocorticotropic hormone (ACTH). This is turn travels down to the adrenal glands, where it stimulates the release of cortisol and other corticosteroids. These hormones activate the sympathetic nervous system. Cortisol influences many psychological responses, including stress, mood, and some forms of mental illness.