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- 1. With Thad Wilson Thyroid Hormones (Thyroxine and Triiodothyronine) Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 2. Hypothalamic Pituitary Thyroid Axis Paraventricular nucleus secretes somatostatin, which targets thyrotropes. Arcuate nucleus and median eminence secrete TRH. Hormone-secreting cells release peptide hormones into the general circulation. Left image: Philschatz, Figure 1, http://philschatz.com/anatomy-book/contents/m46699.html, Download for free at http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.81, CC BY 4.0, Right image: © Lecturio Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 3. Negative Feedback Control Hypothalamus Anterior pituitary thyrotropes Thyroid gland TSH SS TRH T3 + T4 + + Binding proteins Only free hormones participate in feedback. Circulating binding proteins protect thyroid hormones from degradation. + Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 4. Follicular cell Parafollicular cell Colloid Blood vessel Histology of the Thyroid Glands Thyroid gland © by LecturioKatrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 5. Thyroid Hormones • T4 • T3 (most active form) • Reverse T3 Other Intermediates • MIT • DIT Image: John E. Hall, Guyton and Hall Textbook of Medical Physiology, 13th Edition, 2016, p. 953, Saunders (Elsevier) Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 6. Thyroid Hormone Synthesis 1. Iodide is taken up via sodium/iodide symporter (NIS), which transports I- and 2 Na+. 2. Iodide is secreted via pendrin channel, Tg via exocytosis. 3. Iodide is converted to I2 via oxidation. 4. I2 and thyroglobulin combine via iodination to form MIT and DIT. 2 Na+ I- NIS ATP Na+-K+ ATPase Thyroglobulin (Tg) Tg Tg TPO TPO TPO I- I2 MIT DIT Materials to be recycled T3 + T4 T3 rT3 T4 I- T3 + T4 Lysosome Colloid Follicular cell Blood vessel 1. 2. 3. 4. © by Lecturio T4 T3 Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 7. Thyroid Hormone Synthesis 5. MIT and DIT conjugate to form T3 and T4. 6. Colloid is endocytosed into the cell containing bound hormones. 7. Vesicles fuse with lysosomes where proteolytic enzymes cleave bonds holding T3 and T4 which then enter the cytosol. 8. Free T3 and T4 are secreted into the blood. 2 Na+ I- NIS ATP Na+-K+ ATPase Thyroglobulin (Tg) Tg Tg TPO TPO TPO I- I2 MIT DIT Materials to be recycled T3 + T4 T3 rT3 T4 I- T3 + T4 Lysosome T3 T4 Colloid Follicular cell Blood vessel 5. 6. 7. 8. © by LecturioKatrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 8. Thyroid Hormone Transportation • The majority of T4 and T3 is bound to thyroxine- or thyroid-binding globulin (TBG). The remainder of the T4 and T3 is bound to transthyretin or albumin. • -bound) active form. • Free and bound forms are in equilibrium; thus, the amount of free hormones remains fairly constant and has a longer ½ life. (T3 1-day and T4 7-days) Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 9. T4 and T3 enter the cell either by diffusion or by carrier-mediated transport. Peripheral Thyroid Conversion T4 and T3 enter the cell either by diffusion or by carrier-mediated transport. monodeiodinase T4 to T3. T3 shows 10 times the affinity for the THR than T4. Na-K pump Gluconeogenic enzymes Respiratory enzymes Myosin heavy chain b- adrenergic receptors Many others Nucleus mRNA Gene Transcription Thyroid response element (TRE) Retinoid X receptor (RXR) Thyroid hormone receptor (THR) Nuclear envelope T4 T4 T3 T3 I Blood plasma Cytosol © by Lecturio 5 - deiodinase Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 10. Symptomatology Associated with Thyroid Hormones • BMR and weight changes • Thermoregulation • Growth • Goiter • Myxedema and exophthalmos Almazi, PD Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 11. Symptomatology Associated with Thyroid Hormones • BMR and weight changes • Thermoregulation • Growth • Goiter • Myxedema and exophthalmos Edema Exophthalmos Jonathan Trobe, Proptosis and lid retraction from Graves' Disease, https://commons.wikimedia.org/wiki/File:Proptosis_and_lid_retraction_from_Graves%27_Disease.jpg , CC BY 3.0 Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)
- 12. This document is a property of: Katrina Lee Mangin Gagan Note: This document is copyright protected. It may not be copied, reproduced, used, or distributed in any way without the written authorization of Lecturio GmbH. Powered by TCPDF (www.tcpdf.org) Katrina Lee Mangin Gagan, katrinalee.gagan@perpetual.edu.ph © www.lecturio.com | This document is protected by copyright. Powered by TCPDF (www.tcpdf.org)