Definition: The Endocrine Gland is an integral part of the Endocrine System - it produces and releases hormones into the bloodstream. There are a few of these glands dotted throughout the body. The main one - the Pituitary Gland - is situated in the back of the brain and its function is to control the other endocrine glands in the body. Another example of an Endocrine gland is the Thyroid, which regulates metabolism and determines energy levels. The Parathyroid controls levels of calcium in the blood. There is also the Pineal Gland, which manages melatonin levels, which affects our sleep pattern.