What Is the Thyroid Gland?

The thyroid is a butterfly-shaped gland located at the front of your neck, below the Adam's apple.

Structure

• Two lobes connected by an isthmus
• Weighs about 15–25 grams
• One of the largest endocrine glands

What It Produces

• T4 (thyroxine): prohormone, 80% of output
• T3 (triiodothyronine): active hormone, 20% of output
• Calcitonin: regulates calcium (minor role)

What It Needs

• Iodine — essential for hormone production
• Selenium — for T4-to-T3 conversion
• Tyrosine — amino acid building block