Hypothalamic-pituitary adrenal axis

The body's response to stress.


HPA Axis.

The HPA involves interactions between the hypothalamus located in the brain, the pituitary gland located just beneath the brain and the adrenal cortex, part of the adrenal gland - we have two of these located close to our kidneys. 

When the body is experiencing stress, the HPA axis is stimuated, this is done by the hypothalamus which sends messages via neurotransmitters and stimulates the secretion of the hormone adrenocorticotrophic hormone from the pituitary gland. In turn ACTH travels to the adrenal glands where it stimulates the adrenal cortex, in doing so the adrenal cortex releases glucorticoids which increase blood sugar levels to provide more energy.

Being continuously exposed to stress means a constant production of glucorticoids, having a prolonged increase in blood sugar levels may lead to more serious illnesses such as diabetes. 

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Sympathomedullary pathway

SAM pathway.

The SAM pathway involves interactions between the hypothalamus, the sympathetic branch (part of the ANS), and the adrenal medulla - again part of the adrenal gland located close to the kidneys. 

When the body is experiencing stress, the hypothalamus sends messages via neurotransmitters to the sympathetic branch - this is part of the autonomic nervous system and is responsible for the 'fight or flight' response, it increases arousal, blood pressure and heart rate etc. The sympathetic branch then in turn stimulates the adrenal medulla and this is responsible for the secretion of adrenaline and noradrenaline. Adrenaline constricts blood vessels & increases the heart rate whereas noradrenaline increases blood sugar levels. 

Continuous exposure to stress & production of adrenaline can lead to a condition known as hypertension - permanently raised blood pressure. 

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