Thyroxine

• What is thyroxine and where is it produced?

  Thyroxine is a hormone produced by the thyroid gland (in the neck).

  It regulates:

  • Metabolism (rate of chemical reactions in cells).
  • Heart rate and temperature.
  • Growth and development in children.
• How is thyroxine controlled by negative feedback?

  1. Low thyroxine levels detected → Pituitary gland releases TSH (Thyroid-Stimulating Hormone).
  2. TSH stimulates the thyroid gland to release more thyroxine.
  3. Thyroxine levels increase → TSH production stops.

  This maintains a stable level of thyroxine in the body.
• What happens if too much thyroxine is produced?

  • Increased metabolism → More energy used.
  • Weight loss, high heart rate, and sweating.
  • Less TSH produced (negative feedback reduces hormone production).
• What happens if too little thyroxine is produced?

  • Slow metabolism → Weight gain.
  • Low energy levels and fatigue.
  • Cold intolerance (feeling cold often).
  • More TSH is released to stimulate the thyroid gland.