The discovery that the brain contains specific receptors for manufactured opiate drugs such as morphine implies that the body must make an ___ substance that interacts with those same receptors.

ENDOGENOUS

Explanation: Receptors readily binds with biochemical messangers (called ligand) in the body system.

A particular receptor will only bind with a specific ligand, which translates that a specific receptors which readily binds with opiate drugs (such as morphine and oxycodone) for reducing body response to pain, must have been in the past, had an interaction with an endogenous biomolecule similar in molecular composition with that of opioid pain relievers .

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.