A BRIEF OVERVIEW OF THE THYROID GLAND

1. A BRIEF OVERVIEW OF THE THYROID GLAND By April Stoll

2. Anatomy of the Thyroid Gland

3. 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

4. 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 T3is considerably more active • Considered the major metabolic hormones because they target virtually every tissue

5. 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

6. 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

7. 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

8. 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)

9. 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)

10. 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

11. Hypothalamic-Pituitary-Thyroid AxisNegative Feedback Mechanism

12. Hypothyroidism Two common examples are: Iodine deficiency Primary thyroid disease Symptoms include: Lethargy Fatigue Cold-intolerance Weakness Hair loss Reproductive failure Hyperthyroidism The most common form is Graves Disease Is less common than Hypothyroidism Symptoms include: Nervousness insomnia high heart rate eye disease anxiety Thyroid Disorders

13. http://www.methodisthealth.com/endocrin/thygland.htm

14. THE END ??? QUESTIONS ???