Multiple choice Which of the following is NOT an endocrine gland? Adrenal glands Thyroid gland Mammary glands Pituitary gland Reveal answer Fill a bubble to check yourself C Correct answer Explanation Mammary glands are exocrine glands because they secrete milk through ducts to the external environment. In contrast, the adrenal, thyroid, and pituitary glands are endocrine glands that secrete hormones directly into the bloodstream.