Introductory Chapter: Introduction to Thyroid Disorders

Thyroid disorders are most common endocrine problem next to diabetes mellitus. Thyroid disorders affect women more compared to men. Thyroid glands secrete, store, and release triiodothyronine (T3) and thyroxine (T4). The hormone T4 gets converted into T3 at tissue level and produces its effect. Iodine is necessary for production of thyroid hormone. Iodine in food is trapped by thyroid gland and is utilized in hormone production. Pituitary and hypothalamus control thyroid gland hormone secretion. TRH from hypothalamus modulates through pituitary to produce TSH, which in turn controls thyroid hormone production. If T4 and T3 are low, TSH level increases to stimulate thyroid gland to secrete more hormone. T3 and T4 hormones have profound effect on the body. Almost all the tissues are stimulated, and body metabolism is increased. T3 and T4 affect cardiovascular system, GI tract, brain, metabolism, weight, bone, etc. With increased T4 and T3, there is tachycardia, diarrhea, hyperglycemia, lowering of cholesterol, increased growth rate in infant, normal brain development, and sexual function. Undiagnosed hypothyroidism in infants not only affects physical and bony growth but also damages brain growth. If untreated, it leads to permanent damage.