The purpose of the feline thyroid is to control how fast the animal's metabolism functions. This is the same function the thyroid serves in humans. The thyroid takes up iodine from the cat's blood and turns it into a thyroid hormone called thyroxine.
The thyroid stores thyroxine until it is needed. When it is needed, the thyroxine is released directly into the bloodstream. Thyroxine turns into other hormones that control the rate at which cells change oxygen and food into energy.
As in humans, the feline thyroid is found in the throat on either side of the trachea. In cats, the thyroid is actually two organs, while its two lobes are fused in humans.