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Thyroid gland

thyroid gland, structure, function, effects, disorders, regulation, mode of action

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Thyroid gland

  1. 1. Thyroid Gland By: Khuram Aziz M.Phill Biochemistry Scientist by IBC Life sciencesMember of Pakistan Young Scientist Association
  2. 2. Outline• Location• Structure• Synthesis• Mode of action• Effects• Regulation• Disorders
  3. 3. Thyroid gland• Largest gland in the body• Location : in the neck inferior the larynx and spanning over the ventral surface of trachea• Function: – Secretion of thyroxin and triiodothyronine – Secretion of calcitonin
  4. 4. Fig 19-7 Thyroid Gland Anterior surface of trachea just inferior of thyroid cartilage (or Adam’s apple) Two lobes connected by isthmus Microscopic thyroid follicles produce thyroid hormone C Cells - produce calcitonin ( Ca2+)
  5. 5. Structures and Functions of Endocrine System Fig. 48-10. Thyroid and parathyroid glands. Note the surrounding structures. 5 Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.
  6. 6. Thyroid Gland: Hormones and Iodine Metabolism
  7. 7. Synthesis of Thyroid Hormone Blood Follicle Epithelium Colloid MIT+DIT Thyroid Peroxidase I- I- I2 I2 T3 Pump + Na+ TG TG DIT+DIT MIT + Tyrosine DIT -T3 -T4 -T3 T4 T3 -MIT -T4 + T4 TG -DIT TG -MIT -DITThyroid hormone synthesis and secretion involves processes that occur within follicularepithelial cells and in colloid.I-: iodide ions; I2: iodine; TG: thyroglobulin; MIT: monoiodotyrosine; DIT: diiodotyrosine.
  8. 8. Releases of Thyroid Hormone
  9. 9. Synthesis of thyroid hormones1. Iodide trapping – By sodium iodide symporter – Blocked by: • Thiocyanate SCN- • Perchlorate ClO4- • Pertechnetate TcO4-2. Oxidation of iodide – By thyroid peroxidase – Inhibited by: 1. large intake of iodide >150mcgday 2. Thioamides(refer to hyperthyroidism therapy)
  10. 10. Synthesis of thyroid hormones3. Organification – Tyrosine residues of thyroglobulin is iodinated1. Inhibited by large intake of iodide >150mcgday2. Thioamides(refer to hyperthyroidism therapy) – Produce monoiodotyrosine residues MITnd diiodotyrosine residues DIT
  11. 11. Thyroxine and its precursors: Structure & Synthesis Figure 1-1: Thyroid hormones are made from tyrosine and iodine
  12. 12. Synthesis of thyroid hormones4. Coupling – DIT+MIT=T3 – DIT+MIT=T45. Storage : – Along with thyroglobulin6. Exocytosis and proteolysis – Release of T4 & T37. Conversion of T4 to T3 in peripheral tissue
  13. 13. Drugs that inhibit 5’deiodenase• Steroids• Amiodarone• Beta blockers• Thioamides
  14. 14. T4 vs T3T4 T3• Thyroid gland synthesize • Thyroid gland synthesize 9% 90% • 0.4% fr• 0.04%free • active• Not active• Long T12
  15. 15. Mechanism of action of thyroid hormones
  16. 16. Thyroid Gland Thyroid hormones target almost every body cell Can enter cells & bind to intracellular receptors onmitochondria & in nucleus Effects include:  increased ATP production  increased cellular metabolism, energy utilization & oxygen consumption  increased body temperature  growth & development of skeletal, muscular & nervous system in fetus & children
  17. 17. Effects Of Thyroid Hormones On The Cardiovascular System• Increase heart rate• Increase force of cardiac contractions• Increase stroke volume• Increase Cardiac output• Up-regulate catecholamine receptors
  18. 18. Effects Of Thyroid Hormones On The Respiratory System• Increase resting respiratory rate• Increase minute ventilation• Increase ventilatory response to hypercapnia and hypoxia
  19. 19. Effects Of The Thyroid Hormones On The Renal System• Increase blood flow• Increase glomerular filtration rate
  20. 20. Effects Of The Thyroid Hormones On Oxygen Carrying Capacity• Increase RBC mass• Increase oxygen dissociation from hemoglobin
  21. 21. Thyroid Hormone Actions Which Increase Oxygen Consumption• Increase mitochondrial Size,Number and Key Enzymes• Increase Plasma membrane Na-K ATPase Activity• Increase Futile Thermogenic Energy Cycles• Decrease Superoxide Dimutase Activity
  22. 22. Effects Of The Thyroid Hormones On Intermediary Metabolism• Increase glucose absorption from the GI tract• Increase carbohydrate,lipid and protein turnover• Down-regulate insulin receptors• Increase substrate availability
  23. 23. Effects Of The Thyroid Hormones In Growth And Tissue Development• Increase growth and maturation of bone• Increase tooth development and eruption• Increase growth and maturation of epidermis,hair follicles and nails• Increase rate and force of skeletal muscle contraction• Inhibits synthesis and increases degradation of mucopolysaccharides in subcutaneous tissue
  24. 24. Effects Of The Thyroid Hormones On The Nervous System• Critical for normal CNS neuronal development• Enhances wakefulness and alertness• Enhances memory and learning capacity• Required for normal emotional tone• Increase speed and amplitude of peripheral nerve reflexes
  25. 25. Effects Of The Thyroid Hormones On The Reproductive System• Required for normal follicular development and ovulation in the female• Required for the normal maintenance of pregnancy• Required for normal spermatogenesis in the male
  26. 26. Regulation of Thyroid Hormones
  27. 27. Thyroid Gland Function  Thyroxin (T4) and triiodothyronine (T3) speed up metabolic rateGoiter  Calcitonin lowers blood Ca2+ levels  Thyroid pathologies: Exophthalmus Hyper- and Hypothyroidism
  28. 28. Goiter Formation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.• Lack of iodine• Interferes with negative feedback control of TSH• Results in abnormal enlargement of the thyroid gland
  29. 29. HypothyroidismHyperthyroidism Slowing of mind and body
  30. 30. Disease of thyroid glandHypothyroidism Hyperthyroidism• Hashimoto thyroiditis • Graves disease (autoimmune disorder) (autoimmune disease)• Iodine deficiency • Toxic multinodular goiter• Drugs (amiodarone) • Drugs (amiodarone)• Radiation exposure • Thyroid storm(life• Pituitary tumors threatening condition of• Myxedema (life threatening hyperthyroidism) condition of hypothyroidism)
  31. 31. 6. Clinic connection Hyperthyroidism
  32. 32. HypothyroidismCretinism
  33. 33. Apply Your KnowledgeTrue or False: ANSWER:T Thyroid hormones stimulate protein synthesis.__ Thyroid follicles storeF The thyroid gland does not store hormones. some hormones.__ PTH activates osteoclasts.__ PTH activates osteoblasts.F Thyroid hormoneF Calcitonin increases cellular energy production.__ increases cellular energy production.T The four parathyroid glands are located on the thyroid gland.__T Calcitonin lowers blood calcium levels.__ 34-37