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