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Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss the HPA axis.
The hypothalamic-pituitary-adrenal, or HPA, axis is best known for its role in our body’s
reaction to stress.
The HPA axis includes a group of hormone-secreting glands from the nervous and endocrine systems:
the hypothalamus, pituitary gland, and adrenal glands.
The hypothalamus is a small neuroendocrine structure situated just above the brainstem
that controls the release of hormones from the pituitary gland, a hormone-secreting gland
that sits just below the hypothalamus.
The pituitary gland can release hormones into the bloodstream to reach a variety of targets.
In the case of the HPA axis, hormones released from the pituitary gland travel down to the
kidneys and influence the secretion of hormones from endocrine glands called the adrenal glands,
which sit on top of the kidneys.
The primary function of the HPA axis is to regulate the stress response.
When we experience something stressful, the hypothalamus releases a hormone called corticotropin-releasing
hormone (or CRH).
CRH signals the pituitary gland to secrete a hormone called adrenocorticotropic hormone,
or ACTH into the bloodstream.
ACTH travels down to the adrenal glands where it prompts the release of a hormone called
cortisol from the cortex, or outer layer, of the adrenal glands.
The release of cortisol causes a number of changes that help the body to deal with stress.
For example, it helps to mobilize energy like glucose so the body has enough energy to cope
with a prolonged stressor.
When cortisol levels in the blood get high, this is sensed by receptors in areas of the
brain like the hypothalamus and hippocampus, which leads to the shutting off of the stress
response through what is known as a negative feedback mechanism.