Which of the following glands is NOT considered an endocrine gland?

The liver is often not classified as an endocrine gland, despite its various essential functions in the body. Endocrine glands are those that secrete hormones directly into the bloodstream to regulate bodily functions. While the liver does secrete certain substances that can have hormonal effects, such as insulin-like growth factors, it primarily functions as an organ involved in metabolic processes, detoxification, and bile production.

In contrast, the thyroid, pancreas, and adrenal glands all qualify as true endocrine glands because they primarily produce and release hormones that play critical roles in regulating metabolism, blood sugar levels, stress responses, and various other physiological activities. The thyroid gland produces hormones like thyroxine, the pancreas secretes insulin and glucagon, and the adrenal glands release stress hormones, such as cortisol and adrenaline. Thus, identifying the liver as not being an endocrine gland is correct due to its primary roles being metabolic rather than strictly hormonal in nature.