What are chemical messengers produced by endocrine glands that travel through the bloodstream to affect other tissues?

• A. Endocrine glands
• B. Hormones
• C. Pheromones
• D. Neurotransmitters

Answer: (B)

Endocrine signaling uses chemical messengers that travel through the bloodstream to reach distant tissues. These messengers are hormones produced by endocrine glands such as the pituitary, thyroid, adrenal glands, and pancreas. Once in the blood, hormones bind to receptors on target cells to regulate processes like metabolism, growth, and reproduction. This system differs from neurotransmitters, which are released at synapses to produce rapid, local effects on nearby neurons or muscles, and from pheromones, which are chemicals released into the environment to influence other individuals rather than the body's own tissues. Because hormones travel via the bloodstream, their effects are typically slower to start but longer-lasting.