BY2EN2 Endocrinology The Thyroid Gland (week 3) Please make sure you have done any of the asynchronous work required before the synchronous session to make the most of it! When you are watching recordings, please do pause and make notes as well as clarifying things that you don't understand. The slides are all available on Blackboard. Asynchronously before the lecture Watch the recording entitled "Introduction to Thyroid Hormones". This will introduce the thyroid gland and explain how thyroid hormones are made Familiarise yourself with thyroid function testing by reading material found on the website https://labtestsonline.org.uk/tests/thyroid-function-tests Watch the recording entitled "T3 and T4". This will introduce the thyroid hormones, explain. How their actions can be grouped and cover their circulating levels Using the following website, learn about the role of deiodinases in thyroid hormone function: https://thyroidpatients.ca/2018/07/16/three-deiodinases- regulate-t3/ Synchronous session - Attend the synchronous session (and take part!).
Introduction to Thyroid Hormones lecture: This is part of the HPT axis- hypothalamic-pituitary-thyroid axis. Terminology: · TRH - thyrotropin-releasing hormone (releasing hormone- from hypothalamus) · TSH - thyroid stimulating hormone (tropic hormone- from anterior pituitary) · MIT - monoiodotyrosine · DIT - diiodotyrosine • T3 - triiodothyronine · T4 - thyroxine (tetraiodothyronine) · TG - Tg, thyroglobulin · TBG - thyroid binding globulin · D1-D3 - deiodinases . TR - THR, thyroid receptor · RXR - retinoid X receptor (coregulator) Thyroid Gland: Artery - Larynx · Thyroid gland Common carotid artery Trachea (a) Section of one follicle Thyroid follicle (contains colloid) Follicular cells (b) . Sits in throat either side of the trachea. · Bilobular structure . If you take a tissue section of the thyroid gland you would see: o Follicle cells that form a ring around a large colloid containing follicle.
Thyroid Hormone Structures: Tyrosine HO H H -c-C-n=0 H NH2 Thyroxine (T4) 1 I H H O HO 0 -c-C-c 1 - 1 I I OH H NH2 (2 tyrosine + 4 1) Tyrosine HO H H C-C-C OH H NH2 Triiodothyronine (T3) I I I H H -C-C-C HO 0 1 1 1 OH H NH2 (2 tyrosine + 31 ) · Amino acid tyrosine is the precursor for T3 and T4 formation. · Amino acid-based hormones. Action of TSH on the Thyroid: . TSH binds to the thyroid stimulation hormone receptor (TSHR). . TSH is the major controller of thyroid cell function and cell growth, as the thyroid develops through childhood to adulthood. · Mutations in the TSHR may lead to thyroid diseases such as hyperthyroidism. · TSHR is divided into two subunits (alpha and beta), which are linked by disulphide bridges. · TSHR is a GPCR, which is coupled with a Gs or Gq protein. Thyroid hormone synthesis: 1. Iodide is co-transported with Na+ from interstitial fluid across the cell membrane of follicle cells, 2. Iodide diffuses across the follicle cells, where it is pumped by pendrin into the lumen of the follicle, where the colloid is found. 3. Within the colloid iodide is oxidised and attached to