What is the active form of thyroxine produced by the thyroid gland?

The active form of thyroxine produced by the thyroid gland is Triiodothyronine, commonly known as T3. Thyroxine, or T4, is converted into T3 in the body, which is the form that exerts biological effects on tissues and regulates metabolism. T3 plays a vital role in stimulating the metabolic processes in cells, influencing growth, development, and energy expenditure.

In this context, the other options refer to hormones produced by different glands and serve distinct physiological functions. Insulin, produced by the pancreas, is crucial for glucose metabolism; adrenaline, released by the adrenal glands, is involved in the body's fight-or-flight response; and oestrogen, primarily produced by the ovaries, regulates reproductive functions and secondary sexual characteristics. Each of these hormones functions independently and does not pertain to the thyroid's hormonal activity like T3 does.