Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles. This prepares the body for "flight or fight", so it is ready to run away or to face the danger.
Thyroxine is produced by the thyroid gland. It stimulates the basal metabolic rate, which is the rate at which the body uses energy when it is at rest. Thyroxine also plays an important role in growth and development.
The level of thyroxine in the blood is kept within a narrow range by negative feedback. If the thyroxine level rises too high, this change causes the release of thyroxine to be reduced, so the level falls. If the level falls too low, the release of thyroxine increases, so the level rises. Either way, the response reverses the original change and returns the level to normal.