A BRIEF OVERVIEW OF THE THYROID GLAND

A BRIEF OVERVIEW OF THE THYROID GLAND By April Stoll Anatomy of the Thyroid Gland Thyroid Basics: The main function of the thyroid is to control the body’s metabolism Its sole function is to make thyroid hormone This hormone has an effect on nearly all tissues of the body where it increases cellular activity The Thyroid Produces and Secretes 2 Metabolic Hormones  The two principal hormones are: Thyroxine (T4 ) and triiodothyronine (T3) Required for homeostasis of all cells Influence cell differentiation, growth, and metabolism Stimulate protein production in the body’s tissues T4 is the most abundantly secreted, but T3 is considerably more active Considered the major metabolic hormones because they target virtually every tissue Thyroid Hormones Stimulate Metabolic Activities in Most Tissues Regulate the rate of overall body metabolism (specifically T3) T3 increases basal metabolic rate Increases body heat production Calorigenic effects T3 increases oxygen consumption by most peripheral tissues The Chemistry of Thyroid Hormones: Thyroid hormones are derivatives of the amino acid Tyrosine bound covalently to iodine These hormones are basically two tyrosine's linked together with the critical addition of iodine at the three of four positions on the aromatic rings T4/T3 Conversion Sites The liver is the major extrathyroidal T4 conversion site for production of T3 Some T4 to T3 conversion also occurs in the kidney and other tissues Thyroid-Stimulating Hormone (TSH)  Also known as Thyrotropin  Is secreted from cells, called thyrotrophs, in the anterior pituitary, which in turn is controlled by the hypothalamus  Is the major regulator of the thyroid gland  It Regulates thyroid hormone production, secretion, and growth  Is regulated by the negative feedback action of T4 and T3  Its synthesis and release is stimulated by thyroid-releasing hormone (TRH) TSH-cAMP Thyroid-Stimulating Hormone-cyclic Adenosine Monophosphate (cAMP) Is the prime regulator of iodide uptake and concentration T3/T4 formation Induces the expression and activation of the 3 necessary genes that encode proteins involved in iodide uptake and thyroid hormone formation Sodium-iodide symporter (NIS) Thyroglobulin (Tg) Thyroperoxidase (TPO) Thyroid-Releasing Hormone (TRH) Is secreted by hypothalamic neurons Is only a tripeptide, with the basic sequence of amino acids being glutamic acid-histidine-proline Is inhibited by high blood levels of thyroid hormones in the negative feedback loop Is the major positive regulator of TSH secretions Hypothalamic-Pituitary-Thyroid Axis Negative Feedback Mechanism Thyroid Disorders  Hypothyroidism  Two common examples are:  Iodine deficiency  Primary thyroid disease  Hyperthyroidism  The most common form is Graves Disease  Is less common than Hypothyroidism  Symptoms include:  Nervousness  insomnia  high heart rate  eye disease  anxiety  Symptoms include:  Lethargy  Fatigue  Cold-intolerance  Weakness  Hair loss  Reproductive failure http://www.methodisthealth.com/endocrin/thygland.htm THE END ??? QUESTIONS ???