Thyroid gland. Illustration of the human thyroid gland located in the neck, with its associated blood vessels. At lower centre is the two-lobed thyroid gland positioned on the trachea (windpipe, white); the two lobes are joined by an isthmus of tissue & sometimes, as here, a smaller third lobe extends upwards. It is supplied with thyroid blood vessels from the main carotid arteries (red) and jugular veins (blue) of the neck. The thyroid is an endocrine gland that secretes hormones into the blood which regulate energy levels and metabolism, including mental and physical development. Lack of thyroid hormone may give rise to cretinism in infants and myxoedema in adults.