Endocrine refers to which type of secretion?

• A. Internal secretion
• B. External secretion
• C. Nervous control
• D. Immune signals

Answer: (A)

Endocrine refers to internal secretion—the release of hormones into the bloodstream so they travel through the internal environment to act on distant target organs. This is different from exocrine secretion, where glands release substances into ducts that carry them to external surfaces or body cavities, such as digestive enzymes into the gut or sweat onto the skin. Nervous control relies on nerve impulses and neurotransmitters for rapid, targeted signaling at synapses, not primarily through circulating hormones. Immune signals involve cytokines and other immune mediators, which is a separate signaling domain from the classic endocrine pathway. A typical endocrine example is insulin released by the pancreas into the blood to regulate blood glucose.