system
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human
ELI5: If hormones are secreted into blood, and blood needs to pump around the body, how does adrenaline act so quickly

Ive always wondered how the moment of drama and that sinking feeling happen together instantly. But the chemical has to be secreted, get into the blood, and then the blood needs to be pushed via the heart to the brain.

How does this happen so fast? The chemical must be secreted in a way that the blood near the gland gets a very high concentration and I don't think it would diffuse that fast to be evenly distributed throughout the body. Adrenaline is one that comes to mind.
gpt
Blood travels through the body at roughly 3-4 miles per hour. This is at rest and just an average though. When your body wants to get ready for a fight or flight situation, your heart rate goes up. 

Typically a drug injected in the arm, at rest speeds, will hit the brain in just a few seconds. This is assuming a healthy average heart rate, roughly 70-85 bpm. 

A fight or flight response drives the heart rate up to 115-140. The upper bound of which is twice the lower range of resting heart rate. It’s not quite doubling the speed, perhaps, but it’s making it much faster. 

Adrenaline is produced just above the kidneys in special glands. This is roughly in the middle of your body. With a blood speed, under stress, of up to 6-8 miles per hour, the hormone will reach your heart, muscles, and brain, in less than a second and a half. It takes a negligible amount of time to enter your blood, and once there it’s running around body faster than a jogging person.