Now, T three and T four hormones of the thyroid gland are actually controlled and stimulated by a hormone that is produced by our anterior pituitary gland known as the thyroid stimulating hormone or TSH. And TSH itself is stimulating controlled by TRH, the thyroid releasing hormone produced by the hypothalamus. So we have this positive feedback mechanism that allows us to basically control the production and release of T three and T four. And we also actually have a negative feedback mechanism as we'll see in just a moment. So let's begin by discussing the triidothyrene hormone T three and the thyroxine hormone, the T four hormone. Now, inside our thyroid gland, we have a type of cell known as our follicular cell.