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This steroid hormone is more important in altering the body’s metabolism (i.e.

Stress also stimulates the release of adrenocorticotropic hormone from the pituitary gland, which promotes the production of the steroid hormone cortisol from the cortex of the adrenal glands. When the stressful situation ends, the nerve impulses to the adrenal glands are lowered, meaning that the adrenal glands stop producing adrenaline. This process happens relatively quickly, within minutes of the stressful event being encountered. How is adrenaline controlled?Īdrenaline is released mainly through the activation of nerves connected to the adrenal glands, which trigger the secretion of adrenaline and thus increase the levels of adrenaline in the blood. There is a continuous low level of activity of the sympathetic nervous system resulting in release of noradrenaline into the circulation, but adrenaline release is increased at times of acute and chronic stress. Key actions of adrenaline include increasing the heart rate, increasing blood pressure, expanding the air passages of the lungs, enlarging the pupil in the eye (see picture 1), decreasing the sensitivity to pain, improve vision, hearing and other senses, slowing digestion, redistributing blood to the muscles and altering the body’s metabolism, so as to maximise oxygen and nutrients to the body and increase blood glucose levels (primarily for the brain) as seen in picture 2.Ī closely related hormone, noradrenaline, is released mainly from the nerve endings of the sympathetic nervous system (as well as in relatively small amounts from the adrenal medulla). However, the overall effect of adrenaline is to prepare the body for the ‘fight or flight’ response in times of stress, i.e. What are the actions of adrenaline?Īdrenaline has many different actions depending on the type of cells it is acting upon. They are released into the bloodstream and serve as chemical mediators (hormone), and also convey the nerve impulses to various organs (neurotransmitters).

They are produced in the centre ( medulla) of the adrenal glands and noradrenaline is also produced in some nerve cells ( neurons) of the central peripheral nervous system. Image of an eye showing a dilated or enlarged pupil - one of the effects of adrenaline released during a 'fight or flight' response.Īdrenaline and noradrenaline are two separate but related chemical messengers.