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THYROID PHYSIOLOGY
Mohit ChhabraRoll no. 47Guided by Dr. Mohit Joshi
OBJECTIVES
• Understand relevant microscopic anatomy
• Grasp basic concepts of: – Iodine metabolism– Thyroid Hormone Synthesis– Regulation of Thyroid hormone– Actions of thyroid hormone
MICROSCOPIC ANATOMY OF THYROID
• Thyroid Follicular Unit
• C Cells
IODINE METABOLISM
THYROID HORMONE SYNTHESIS
1. Thyroglobulin is synthesized in RER of Follicular Cells
2. Formation and transport of Tg in exocytotic vesicles into the lumen
3. Iodide transport4. Iodide oxidation5. Iodide Storage in lumen6. Endocytosis by pseudopods & colloid droplet formed7. Fusion with lysosomes Hydrolysis &
Secretion8. Deiodination
THYROID PEROXIDASE
THYROID HORMONES• Occurs in 2 forms• Free form in plasma• Bound form– Bound to:
AlbuminTBGTBPA
• Fluctuations in binding
REGULATION• T3 and T4 levels play a pivotal role
• Negative feedback loop
• Affect on TSH and TRH
• Auto regulatory mechanisms
MECHANISM OF ACTION
• Thyroid hormone is LIPOPHILIC• Binds to nuclear receptors in the nucleus• Appropriate Hormone Response Element
comes into action• Transcription and Translation occurs with
respect to the function of the hormone in that cell
ACTIONS OF THYROID HORMONES
CalorigenicGrowth & Development & Effects on Nervous
SystemEffects on Cardiovascular SystemEffects on carbohydrate metabolismEffects on cholesterol metabolismEffect on Catecholamines
SOURCESGoogle Image Search
Bailey & Love’s Short Textbook of Surgery
Sabiston’s Textbook of Surgery 18th edition
Ganong’s Review of Physiology