Q and A: about health and research

Thyroid hormones are chemical messengers produced by the thyroid gland that circulate through the bloodstream and influence cells throughout the body. Their primary role is the regulation of metabolism, but thyroid hormones also affect brain function, mood, cognition, and behavior. The Brain–Pituitary–Thyroid Axis Thyroid function is regulated through a three-step hormonal system known as the hypothalamic-pituitary-thyroid (HPT) axis. The hypothalamus, located in the brain, releases thyrotropin-releasing hormone (TRH). TRH stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland in the neck to produce thyroid hormones, primarily T4 (thyroxine). T4 is subsequently converted into the more biologically active hormone T3 (triiodothyronine). This regulatory system allows the brain to influence how much thyroid hormone circulates throughout the body. Thyroid Hormones and Metabolism One of the major functions of thyroid hormones is to ...

Hypothyroidism happens when the thyroid gland doesn't make enough thyroid hormone. This condition also is called underactive thyroid. Hypothyroidism may not cause noticeable symptoms in its early stages. Over time, hypothyroidism that isn't treated can lead to other health problems, such as high cholesterol and heart problems. Hypothyroidism symptoms may include:     Tiredness.     More sensitivity to cold.     Constipation.     Dry skin.     Weight gain.     Puffy face.     Hoarse voice.     Coarse hair and skin.     Muscle weakness.     Muscle aches, tenderness and stiffness.     Menstrual cycles that are heavier than usual or irregular.     Thinning hair.     Slowed heart rate, also called bradycardia.     Depression.     Memory problems. Credi...