thyroid

Introduction

Normal adult size: 15-20 grams

Structure

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

⧼aaushi-heading-embryology⧽

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

⧼aaushi-heading-development⧽

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

More general terms

• endocrine gland

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

Additional terms

• desiccated thyroid (Armour, Niva, Apur)
• thyroid function test

Component of

• neck

Components

• thyroid follicle