Thyroxine - GCSE Biology Definition

Thyroxine is a hormone made by the thyroid gland in the neck. It plays an important role in regulating metabolism, which is the sum of all the chemical reactions in the body that keep cells alive and working, including those that release energy from food. By controlling the rate of these reactions, thyroxine affects how fast or slow different processes happen in the body. It also supports growth and development, especially in children, and influences how the heart and muscles function. If the body produces too much or too little thyroxine, it can lead to health problems such as tiredness, weight changes, or unusual activity levels.