The thyroid and parathyroid are glands located in the lower part of the neck. Both the thyroid and parathyroid glands are endocrine glands. This means they make and release hormones – chemicals which can be released into the bloodstream. These hormones act as messengers, affecting cells and tissues in distant parts of your body. Thyroid hormones affect the body’s metabolic rate and the levels of certain minerals in the blood. The hormone produced by the parathyroid also helps to control the amount of these essential minerals. A simple blood test can determine whether the gland is producing the right amount of hormone.