Final answer:
Norepinephrine, or noradrenaline, is a hormone and neurotransmitter integral to the fight-or-flight response, increasing blood glucose, blood flow to muscles and essential organs, while also serving as a treatment for certain respiratory conditions. It affects the heart rate and can induce arrhythmias during significant releases. It is also significant in mental health, affecting the evaluation of mental health medications.
Step-by-step explanation:
Norepinephrine, also known as noradrenaline, is a non-steroid catecholamine hormone and neurotransmitter produced by the medulla of the adrenal glands and the nervous system. It plays a key role in the body's fight-or-flight response to stress. When a stressful situation arises, norepinephrine, along with epinephrine, is released, leading to several physiological changes. These include increasing blood glucose levels, enhancing blood flow to the muscles and essential organs like the heart and brain, while restricting it to less vital areas such as the skin and digestive system. Additionally, norepinephrine causes the contraction of the capillaries in the mucous membranes, which makes it useful as a remedy for conditions like colds, hay fever, and asthma.
In situations of extreme stress, these hormones also halt kidney function temporarily, particularly affecting blood flow into the nephrons, and activate the renin-angiotensin-aldosterone system. In the nervous system, norepinephrine acts as a neurotransmitter and is involved in mental health; an important aspect to consider when evaluating antidepressants and other related medications.
Both norepinephrine and epinephrine can also cause an increase in heart rate and force of contraction through their action on beta-1 receptors, and potentially induce arrhythmias during massive releases coupled with sympathetic stimulation. Despite these powerful effects, the adrenal medulla does not receive parasympathetic stimulation, which is the part of the autonomic nervous system that would typically counterbalance the sympathetic stimulation.