thyroxine

• thyroxine is a hormone released by the thyroid gland which is in the neck
• thyroxine regulates the basal metabolic rate - the speed at which reactions in the body occur while the body is at rest
• thyroxine is also important for loads of processes in the body, such as stimulating protein synthesis for growth and development
• thyroxine is released in response to thyroid stimulating hormone (TSH) which is released from the pituitary gland
• a negative feedback system keeps the amount of thyroxine in the blood at the right level
• when the level of thyroxine in the blood is higher than normal, the secretion of TSH from the pituitary gland is inhibited (stopped)
• the secretion of TSH is stopped - this reduces the amount of thyroxine released from the thyroid gland, so the level in the blood falls back down to normal