Which of the following is not typically considered a primary endocrine gland?

• A. Spleen
• B. Pineal gland
• C. Pancreas
• D. Thymus

Answer: (A)

Understanding what counts as a primary endocrine gland means focusing on organs whose main job is to produce and release hormones into the bloodstream to regulate other parts of the body. The spleen does not fit that role. Its primary functions are immune surveillance, filtering blood, and recycling old red blood cells. It doesn’t generate hormones that coordinate body-wide processes.

In contrast, the pineal gland makes melatonin to help regulate sleep-wake cycles. The pancreas has an endocrine portion (the islets of Langerhans) that secretes insulin and glucagon to control blood glucose. The thymus releases thymic hormones that influence immune cell development. These hormone-secreting roles are why those organs are considered endocrine sources, whereas the spleen is not.