Final answer:
The largest pure endocrine gland in the body is the thyroid gland, which is key in controlling metabolism and energy use in cells.
Step-by-step explanation:
The largest pure endocrine gland in the body is the thyroid gland. It is located in the neck and plays a crucial role in metabolism, controlling how quickly cells use energy and make proteins. The thyroid, along with other endocrine glands such as the pituitary gland, adrenal glands, and pancreas, secrete hormones into the interstitial fluid, which then diffuses into the bloodstream to be carried to various organs and tissues within the body. As part of the endocrine system, these hormones act as chemical messengers to control many important functions, including growth, metabolism, and sexual development. The pituitary gland is often referred to as the master gland of the endocrine system because it produces hormones that control other endocrine glands, like the thyroid, adrenal glands, and gonads.