Final answer:
Hormones are powerful chemical substances produced by the endocrine glands, traveling through the bloodstream to regulate physiological processes throughout the body.
Step-by-step explanation:
The correct answer to the question is D) Hormones. Hormones are powerful chemical substances secreted by the endocrine glands and are carried throughout the body by the bloodstream. Unlike neurotransmitters that have a localized effect, hormones have body-wide effects because they can reach any cells that contain receptors for them, even though they act more slowly. Endocrine hormones like steroids and amino acid derivatives work as chemical messenger molecules and are crucial in regulating various physiological processes within the body.