Thyroid

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Contents 1 More Specific Terms 2 Introduction 3 More General Terms 4 Additional Terms 5 References

More Specific Terms

• accessory thyroid gland, (suprahyoid/prehyoid/Wolfler gland, thyroideaima)
• lingual thyroid
• sheath of thyroid gland
• thyroid isthmus
• thyroid pyramidal lobe; Lallouette pyramid; Morgagni appendix

Introduction

• Normal adult size: 15-20 grams

• Embryologic origins:

• evagination of pharyngeal epithelium
• some contribution from lateral pharyngeal pouches
• decent of thyroid gives rise to thyroglossal duct: remnants of thyroid persisting along this tract:

• lingual thyroid
• thyroglossal cyst or nodule
• pyramidal lobe of thyroid, a structure contiguous with the thyroid isthmus

• Thyroid development:

• ability of thyroid to concentrate & organify iodine at 10 weeks of gestation
• T4 & TSH present in blood during 2nd trimester
• maternal TRH crosses placenta; maternal TSH does not
• T3 detectable late in 2nd trimester, but concentrations remain low throughout gestation
• rT3 is increased in fetal blood & amniotic fluid relative to maternal blood

• Morphology of adult thyroid:

• 2 lobes joined by isthmus
• anterior & caudad to cartilages of larynx
• fibrous septa divide gland into pseudolobes composed of

• follicles or acini

• cuboidal epithelium
• colloid lumen containing thyroglobulin

• network of capillaries surrounding follicles

• C cells

• source of calcitonin
• give rise to medullary carcinoma

More General Terms

• endocrine gland

Additional Terms

• thyroid function test

References

Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1931

thyroid