Which system makes hormones that are released into the bloodstream to travel to all parts of the body?

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

Answer: (A)

Signals made into hormones and released into the bloodstream are a defining feature of the endocrine system. Glands without ducts secrete these hormones directly into the blood, which then carries them to distant targets throughout the body. The hormones bind to specific receptors on or in those target cells, producing widespread or targeted effects that help regulate metabolism, growth, and other long‑term processes.

In contrast, the nervous system relies on neurons and rapid neurotransmitter release across synapses for fast, local signaling to specific tissues. The digestive system focuses on breaking down and absorbing nutrients, while the immune system defends against pathogens, with signaling primarily through immune mediators rather than broad hormonal distribution.