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?


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

It only takes a couple of seconds for adrenaline released from your kidneys to reach the rest of your body , so as soon as it reaches that tissue it will have an effect , i.e.braised heart rate , resp rate etx

Actually just learned this last semester!

The ELI5 version is that the hormone “adrenaline” flows through your bloodstream (endocrine system) and attaches to receptors on the cells of your heart muscles (could be wrong on the exact location) and causes a change in the cells and tells your heart to beat faster, which is why you feel more flush and why sometimes you can feel your heart beating through your chest.

The endocrine system is surprisingly fast, and rightfully so, because if you’re in a life or death situation you need that adrenaline NOW. That’s why it’s called the “fight or flight” response, sometimes.

A more in depth way of explaining why they happen so fast also has to do with the amount of change that occurs in the cell due to a cascading event starting from one molecule, which turns on a bunch of other proteins, and so on and so forth until one molecule essentially turns on dozens or hundreds of other molecules responsible during the adrenaline response.

Some of my thoughts could be wrong, someone will have to correct me as i am pulling from memory and on mobile.

Edit: “feeling” to “response”

Edit: Some others have added some additional, useful details. Credit where credit is due:





had some ELI5 and some non-ELI5 responses that add information I left out or did not know. Thanks!

Your brain also contains neurotransmitters that are stimulating. SO when you are frightened nerve cells will release norepinephrine in the brain which increases arousal, vigilance, etc. This would be the initial sensation at fright followed very quickly by the release of adrenaline which stimulates heart rate, etc.

Too comment is the most accurate. But to help you understand why everything is so fast realize this: your body is only a couple feet long; your blood is traveling around 3mph.

Your heart is one of the hardest working muscles in your body for a reason. Your blood travels fast and your lymph travels nearly as fast(?)

So adrenaline is a neuro-hormone which means it’s release can be triggered by the electrical impulses from your brain. This makes the release of it suuuuper quick and it also happens to come from your adrenal glands above the kidneys, and the kidneys are getting 20-25% of all your blood flow which makes it circulate through the body super fast. The receptors for it are all on the surfaces of cells so it’s recognized pretty quickly too and the response is multiplied over a few stages inside the cell which gives it a quick and robust response. It’s basically just a speedy process overall

I think you are confusing the neurotransmitters epinephrine/ norepinephrine (aka adrenaline/ noradrenaline) with the hormone cortisol. The immediate response is so fast because norepinephrine works entirely in the brain and signals near instantly to affect your activity, heart rate, and breathing. The signal travels down the spine to the adrenal glands where epinephrine is released into the blood stream causing blood vessels to constrict, glucose to be used, and muscles to respond. After a couple hours, the hormone cortisol is secreted into the blood stream from the adrenal gland to maintain this burst if needed.

Adrenaline and noradrenaline are both neurotransmitters (think fast acting) that have hormone properties. Most hormones act much slower because they travel in the bloodstream, whereas these two function together in the brain with electrical signaling speed.

Fun fact: tyrosine the dietary amino acid is converted to dopamine (pleasure molecule), which is converted to noradrenaline, which is then converted to adrenaline…

So there are already a ton of responses in this thread which explain it better than i can, i just want to add a reason why your heart can change its tune so quickly. You have a node in your heart which is called the sinus node. It has a “natural” tact of approximately 120 Beats per minute. As you know your resting heartrate is quite a bit lower (around 60-80). This is because your sinus node gets constantly throttled by your parasympathetic nervous system. Imagine someone who is pushing against a door -your sinus node- and someone holding against it from the other side -your nervous system-. If you experience a stimulus which needs a higher heartrate your parasympathetic system just stops blocking the door. Your sinus node suddenly has no resistance and burst through the door with full speed. This change can occur between two heartbeats so that this is the fastest way for your body to raise its heartrate.

Those are not purely hormonal. There are nerves in your heart and other organs and the nervous system has ways to regulate the rhythm of your heart, your breathing rate, oxygen and blood supply tp your organs, etc.

See here:

>**Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction**
*You don`t need those when you are in panic and it also reduces bleeding from minor cuts*

>**Blood flow to skeletal muscles and the lungs is enhanced** (by as much as 1200% in the case of skeletal muscles)
*Run faster*

>Dilates bronchioles of the lung through circulating epinephrine, which **allows for greater alveolar oxygen exchange**
*Get more oxygen*

>**Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for enhanced blood flow to skeletal muscles**
*Run, Forest, run!*

>Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and enhances far vision

>Provides vasodilation for the coronary vessels of the heart

And here:

>Constricting the bronchiolar diameter **when the need for oxygen has diminished**

>Dedicated cardiac branches of the vagus and thoracic spinal accessory nerves **impart parasympathetic control of the heart (myocardium)**

Or see this paper about the heart nervous system in heart transplant patients:

>Furthermore, the exercise capacity in denervated HTx recipients seems to be diminished because **denervated hearts must rely on circulating, rather than cardiac, catecholamines (CAT) release to adapt to the increased needs of exercise,** although this adaptation is insufficient to reach normal heart rate (HR) and contractility.21 Early cardiac denervation in HTx recipients leads to the loss of the normal nocturnal decline in blood pressure.16 **It also causes a higher than normal HR at rest, and, in response to exercise, the HR increases more slowly than normal to reach a lower maximal HR, which descends during recovery from exercise at a slower than normal rate.** In addition, cardiac denervation causes an abnormal cardiac output (CO) response to exercise.

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.

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.

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).

Hey! So hormones dont actually work very quickly at all. In fact they move quite slow! Hormones get created in response to certain internal or external stimuli and then shipped through the body via the blood stream. As they move through your body they interact with different areas and cause wide spread responses. Think of them as slow, whole body action grenades. The high speed action molecule you are thinking of is a neurotransmitter.

Neurotransmitters are small molecules that are directly targeted at specifics areas to create instant responses. A good example is seratonin dumps in your brain when something goes happens to you! Cells in your brain will dump large amounts of seratonin or dopamine into the areas between cells ( the synaptic cleft ) and these molecules will bounce around like pinballs dinging receptors that then cause other cells to do the same. These kind of interactions happen really quickly in a target area and tend to have short term effects on your body.

So if your body needs a fast fight or flight type response like being excited by a kiss, it will use neuro transmitters to communicate across cells. If it wants a slow and steady change to the body like increasing muscle it will use an hormone like testosterone that it can ship throughout the body via the blood stream.

Tldr: Hormones are slow, and illicit whole body reactions, neurotransmitters are quick targeted reactions between cells.