Thyroid is a large gland present in neck, around the trachea, just at the junction of larynx and trachea. This makes option A incorrect. Gonads (testes and ovaries) serve as endocrine organs and secrete androgens and estrogen and progesterone respectively. This makes option B incorrect. Pancreas is a large organs present in abdomen and serves as both endocrine and exocrine organ. The endocrine parts of pancreas are islets of Langerhans that produce and secrete insulin and glucagon hormones. This makes option C incorrect. Pituitary gland is located in sella turcica, the groove of sphenoid bone of the skull in the brain. This makes option D correct. Correct answer is D.