Adrenaline and Thyroxine

• Adrenaline

  a hormone that is released by the adrenal gland
• Adrenaline is released in response to stressful or scary situations - your brain detects a fear or stress and sends nervous impulses to the adrenal glands, which respond by secreting adrenaline
• Adrenaline gets the body ready for 'fight or flight' by triggering mechanisms that increase the supply of oxygen and glucose to the cells in the brain and muscles, e.g. adrenaline increases heart rate
• Your body can control the levels of hormones (and other substances) in the blood using negative feedback systems
• When the body detects that the level of a substance has gone above or below the normal level, it triggers a response to bring the level back to normal again
• Thyroxine

  a hormone released by the thyroid gland
• Thyroxine helps to regulate the basal metabolic rate - the speed at which chemical reactions in the body occur while the body is at rest
• Thyroxine is also important for lots of processes in the body, such as stimulating protein synthesis for growth and development
• Thyroxine is produced in response to thyroxine 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, which reduces the amount of thyroxine released from the thyroid gland, so the level in the blood falls back towards normal