Hormones And The Hpa Axis - What Causes Depression: Depression

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Hormones and the HPA axis

Just as neurotransmitters help ferry signals along nerve pathways, other complex chemicals called hormones carry messages to organs or groups of cells throughout the body. These chemicals trigger or regulate certain activities, such as the release of an egg from a woman's ovary and the delicate control of blood sugar levels.

The hypothalamus in your brain, the pituitary gland below your brain, and the adrenal glands atop your kidneys form a trio known as the hypothalamic-pituitary-adrenal (HPA) axis. Together these structures govern a multitude of hormonal activities in the body and may play a role in depression as well.

The hypothalamus secretes corticotropin-releasing hormone (CRH), a hormone vital to rousing your body when a physical or emotional threat looms. This hormone follows a pathway to your pituitary gland, where it stimulates the secretion of adrenocorticotropic hormone (ACTH), which pulses into your bloodstream. When ACTH reaches your adrenal glands, it triggers the release of cortisol. The boost in this hormone prompts a cascade of reactions in your body that can help you respond quickly to a threat.

Stress hormones race through your bloodstream, preparing you to fight or flee. Your heart beats faster — up to five times as quickly as normal — and your blood pressure rises. Your breath quickens as your body takes in extra oxygen. Sharpened senses, such as sight and hearing, make you more alert. This release of stress hormones is often called the stress response.

Normally, a feedback loop allows the body to turn off these defenses when the threat passes. In some cases, though, the floodgates never close properly, and cortisol levels rise too often or simply stay high. This can contribute to problems such as high blood pressure, immune suppression, asthma, and possibly depression.

Studies have shown that people who are depressed or have dysthymia typically have increased levels of CRH. Antidepressants and electroconvulsive therapy are both known to reduce these high CRH levels (see "Medications used for depression and bipolar disorder" and "Electroconvulsive therapy"). As CRH levels return to normal, depressive symptoms recede.

CRH is also distributed through the cerebral cortex, part of the amygdala, and the brainstem. When you face severe stress, this hormone is thought to play a major role in coordinating your hormonal defenses, thoughts and behaviors, emotional reactions, and involuntary responses. The neural pathways that carry the effects of CRH beyond the HPA axis reach other regions of the brain as well, and they link with neurons that release serotonin and norepinephrine. Disturbances in hormonal systems, therefore, may well affect neurotransmitters and vice versa. Research suggests that trauma during childhood can negatively affect the functioning of CRH and the HPA axis throughout life.

Last updated:	January 23, 2007