Thyroxine and adrenaline – Higher

Thyroxine is produced by the thyroid gland, which stimulates the basal metabolic rate. It controls the speed at which oxygen and food products react to release energy for the body to use. Thyroxine plays an important role in growth and development. Thyroxine levels are controlled by negative feedback.

A visual to show the location of the thyroid gland in the human body.

The hypothalamus and pituitary gland have important roles in detecting and controlling thyroxine levels.

  1. Low thyroxine levels in the bloodstream stimulate the hypothalamus to release TRH (Thyrotropin releasing hormone) and this causes the pituitary to release TSH (Thyroid stimulating hormone) so the thyroid releases more thyroxine. So blood levels return to normal.
  2. Normal thyroxine levels in the bloodstream inhibit TRH release from the hypothalamus and this inhibits the release of TSH from the pituitary, so less thyroxine is released from the thyroid gland and normal blood levels are maintained.

This is an example of negative feedback.

Adrenaline is produced by the adrenal glands in times of fear or stress. It targets vital organs, increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for 'flight or fight'.

Adrenaline is controlled by positive feedback.

When adrenaline is released into the bloodstream, it creates multiple effects:

  • an increase in pulse rate and volume of blood pumped by the heart with each beat
  • increase in the depth of breathing
  • dilation of the blood vessels supplying muscles

The effects of adrenalin allow the body to prepare for action in situations where a quick response may be essential.

Adrenaline is then converted into a less active compound by the liver.