If adrenaline is a hormone why is its effect more like those of the nervous system explain this statement?

Answer 1

Adrenaline (aka epinephrine) is a hormone, but bears striking resemblance to the neurotransmitters used in your nervous system.

You see, your nervous system works by a series of synaptic junctions. That is, all your nerve cells are lined up from head to tail, and depolarization waves carry messages down the length of the cells. Synapases are the small gaps between each cell and the next in line. Once the depolarization wave gets to the end of the cell, it cannot just "jump the gap", but it signals the cell to release neurotransmitters. The neurotransmitters are molecules that fit like a lock and key into receptors on the next cell in line. When the neurotransmitters make contact with the receptors on the next cell, it causes a depolarization wave in that one as well, and the process goes on.

In the case of the sympathetic nervous system (your fight or flight nerves), the main neurotransmitter is called norepinephrine. It is what is used in these tiny doses at the end of each nerve cell (generally). When epinephrine (adrenaline, to use the British term) is released from your adrenal gland, it travels through the blood stream and hits the same receptors that norepinephrine normally hits. It is what we call a "direct agonist response." This causes general sympathetic (fight or flight) reactions, such as bronchial dilation, increased heart rate, blood vessel dilation, capillary contraction, and pupil dilation.

I wish I could draw the molecules epinephrine and norepinephrine on here, and you would be able to see how similar they are and why they would both bind to the same receptors. I suggest looking up their structures for a better idea.