Understand that insulin is a hormone involved in regulating blood glucose levels by facilitating cellular glucose uptake.
Recall that insulin is produced by specialized cells called beta cells, which are located in clusters known as the islets of Langerhans.
Identify the endocrine gland that contains the islets of Langerhans; this gland is the pancreas.
Recognize that the other options (adrenal cortex, thyroid gland, anterior pituitary) produce different hormones and are not responsible for insulin production.
Conclude that the pancreas, specifically the beta cells within the islets of Langerhans, is the endocrine gland that produces insulin.