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?

Question

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

Answer 1

Short and very simple answer (in numbered bullets).

1) **The major chemical messenger for fight/flight response is adrenaline (epinephrine).** **It is released into your blood from the “adrenal” glands** (they sit on top of your kidneys. They have epinephrine premade and ready for release).

2) **The Adrenal Glands respond directly to nerve impulses from the brain. Nerves are extremely fast.** (Just like a baseball player can swing a bit at a 90mph fast ball in a split second — your brain sees a tiger charging at you and says ‘fire up the fight or flight response’).

3) **Your blood pumps very fast, so the message spreads everywhere.** (Roughly 100% of your blood volume is pumped through your heart every minute (avg. cardiac output 4-6L, avg. blood volume ~5L). Adrenaline makes your heart pump harder and faster (propelling the ‘fight or flight’ message to your body even faster). (Furthermore your ‘most important organs’ brain, heart, lungs, kidneys, liver get like 75% of your cardiac output — so they get the message louder and faster).

4) **Other nerves in the “sympathetic nervous system”** (part of your ‘auto-pilot’ autonomic nervous system) **control a lot of other specific responses as well.** (Again, nerves are lightning fast — they locally release a neurotransmitter (a chemical that conducts a nerve’s message to an organ or muscle) called ‘NorEpinephrine’ (or NorAdrenalin) at a number of specific organs — an example is your pupils getting big. This nervous input also occurs to increase heart rate).

TL;DR : Nerve signals are lightning fast and start up the increased heart rate / big pupils stuff. Nerves also tell your body to release adrenaline into blood. Blood travels really quickly to the major organs.