Which organ is commonly recognized as an endocrine gland?

• A. Thyroid
• B. Kidney
• C. Spleen
• D. Lungs

Answer: (A)

The key idea is what defines an endocrine gland: it releases hormones directly into the bloodstream to act on distant targets. The thyroid fits this perfectly. It is a ductless gland that releases thyroid hormones (primarily T3 and T4) into the blood, where they travel to almost every tissue to regulate metabolic rate, heart rate, temperature, and development. This hormone release is controlled by the pituitary gland via thyroid-stimulating hormone and operates through a negative-feedback loop, so hormone levels in the blood rise and fall in a balanced way. While other organs like the kidneys have important hormonal roles (such as producing erythropoietin) or the spleen and lungs have primary duties in immunity and gas exchange, they’re not classed as endocrine glands in the same way. The thyroid’s defining feature—the direct release of hormones into the bloodstream to reach distant targets—makes it the best answer.