Thyroid hormones - image description

This diagram shows how the brain controls T3 and T4 levels in your blood. It shows a circle made up of 4 arrows pointing in a clockwise direction. Normal levels are at the top of the circle. Going round in a clockwise direction, it shows how decreased levels of T3 and T4 make your hypothalamus release thyroid-releasing hormones (TRH). These make your pituitary gland release thyroid-stimulating hormone (TSH), which then makes the thyroid gland release T3 and T4. The levels are restored and this completes the circle back to normal levels.