Which of the following is not listed as an endocrine structure in the material?

• A. Liver
• B. Pineal gland
• C. Thymus
• D. Thyroid

Answer: (A)

Endocrine structures are organs that release hormones directly into the bloodstream to influence distant tissues. In your material, the pineal gland, thymus, and thyroid are described as endocrine glands because they secrete hormones that travel via blood to regulate body functions—melatonin from the pineal, thymic hormones from the thymus, and thyroid hormones from the thyroid. The liver, however, is not listed as an endocrine structure in that material; its main roles are metabolic, synthetic, and excretory functions rather than acting as an endocrine gland. So the liver is the one not listed as an endocrine structure.