Thyroxine is made by the thyroid gland in the neck. It controls the metabolic rate, which is the speed of the chemical reactions in the body. It also helps normal growth and development.
Thyroxine level is kept steady by negative feedback. The pituitary gland releases TSH, which stimulates the thyroid to release thyroxine. If the thyroxine level in the blood rises too high, the pituitary releases less TSH, so the thyroid makes less thyroxine and the level falls back. If the level falls too low, the pituitary releases more TSH and the level rises. In negative feedback, a change causes a response that reverses the change.
Adrenaline is made by the adrenal glands, which sit above the kidneys. It is released in frightening or exciting situations and prepares the body for fight or flight. It makes the heart beat faster, so more blood carrying oxygen and glucose reaches the muscles. It also makes the liver release glucose, which the muscles use in respiration to release energy.
