Which organ system uses glands to release chemical messengers that travel through the bloodstream?

Which organ system uses glands to release chemical messengers that travel through the bloodstream?

• A. Nervous System
• B. Endocrine System
• C. Immune System
• D. Digestive System

Answer: (B)

Glands release hormones, which travel through the bloodstream to coordinate activities across distant tissues. This is the central idea of the endocrine system: ductless glands like the pituitary, thyroid, and adrenal glands secrete chemical messengers that circulate in blood to regulate metabolism, growth, and stress responses. In contrast, the nervous system sends rapid, targeted signals through neurons releasing neurotransmitters at synapses, and the digestive system primarily uses enzymes and local signals to process food. The immune system uses signaling molecules too, but its main communication isn’t through hormones released into the blood by glands, making the endocrine system the best fit for this mechanism.

Glands release hormones, which travel through the bloodstream to coordinate activities across distant tissues. This is the central idea of the endocrine system: ductless glands like the pituitary, thyroid, and adrenal glands secrete chemical messengers that circulate in blood to regulate metabolism, growth, and stress responses. In contrast, the nervous system sends rapid, targeted signals through neurons releasing neurotransmitters at synapses, and the digestive system primarily uses enzymes and local signals to process food. The immune system uses signaling molecules too, but its main communication isn’t through hormones released into the blood by glands, making the endocrine system the best fit for this mechanism.