The thyroid gland is located in the neck and produces thyroid hormones. These are called thyroxine (T4) and tri-iodothyronine (T3) and are carried round the body in the bloodstream. They help to keep the body's functions (the metabolism) working at the correct pace.
This is a companion discussion topic for the original article at https://patient.info/hormones/thyroid-and-parathyroid-glands/underactive-thyroid-gland-hypothyroidism