If something is scary or stressful, your hypothalamus sends signals to pituitary and adrenal glands, which let out hormones (a fancy word for messengers) to tell the rest of the body what to do.
Adrenal glands let out a hormone called epinephrin into the blood, which gets your body ready to fight bad guys or high-tail it outa there!
Muscles feel tense & ready to karate chop your enemies!
Lungs breathe fast & shallow to get extra oxygen to your muscles
Salivary Glands make less saliva, leads to dry mouth & you get less chatty
Sweat Glands make your hands sweaty
Pupils get bigger
Liver lets sugar into the blood for muscle power
Heartbeat & blood pressure turn up!
Example: "Acrobatics -- Now that's an adrenalin rush!"