How do hormone responses occur so rapidly? When people are frightened/surprised, they can almost immediately feel a rush of adrenaline and heart rates rise, faces flush, etc. How do hormones reach appropriate organs so quickly? Why isn’t there more of a delay for the hormones to travel?
In: Biology
As said before, blood travels at roughly 3mph. That sounds really slow, until you realize it’s about 4.4 feet (140cm)/sec. Nerve transmissions are a couple of orders magnitude faster (60-100m/sec, depending on nerve type).
So, also as said before, brain receives and processes the stimulus very quickly (signals can go 10cm, or one side of the brain to another, in 0.1sec or less.
Parasympathetic blocks at this point (norepinephrine released in the brain), so sympathetic runs without restraint (fight or flight kicks in). One or two tenths of a second later, the impulses hit the adrenals, which release adrenaline into the bloodstream. It then travels less than a foot, in less than a couple tenths of a second, to receptors in the heart and lungs (heart rate, heart force, artery compression, breath rate, and breath volume all increase). This is why your startle response usually goes “oh sh^t .. OH SH^T”.
It takes a couple seconds longer to get to the skin (sweat, and either hot or cold skin depending on core body needs – more blood or dump heat).
At rest, your blood flows at 4 miles per hour. But your body is only about 5.5 feet tall. So if you do some math, you can say that your blood travels from toe to skull once every second (if you talk big blood vessels it is a little bit faster, if you talk small vessels it is way slower).
When you get scared, your heart beats faster which makes your blood flow faster. Up to about twice as fast.
That means it only takes half a second (a little less) for blood from anywhere in your body to get anywhere else if it travels through the big blood vessels.
Then consider that when scared, your adrenaline is starting from your kidney. It enters your blood in the middle of the body so it needs less time to get to the important places.
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