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Thyroid Anatomy

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Thyroid Anatomy, Thyroid Physiology, Thyroid, Thyroid Gland

  • Embryology
  1. Develops from Tongue root (foramen cecum)
  2. Formed by 5th-6th week of development
  • Anatomy
  1. Images
    1. ThyroidAnterior.gif
  2. Normal Adult Thyroid weighs 20-25g
  3. Components
    1. Two Lateral lobes
    2. Isthmus centrally connects the lobes
  4. Near structures
    1. Recurrent laryngeal nerve
    2. Parathyroid Glands
  • Physiology
  1. Stressors stimulate increased Thyroid function
    1. Puberty
    2. Pregnancy
    3. Physiologic stress
  2. Hypothalamus
    1. Thyrotropin Releasing Hormone (TRH) released
    2. TRH passes down pituitary stalk to pituitary
  3. Anterior Pituitary
    1. Thyroid Stimulating Hormone (TSH) released
    2. TSH passes into circulation to Thyroid
  4. Thyroid
    1. Iodine is absorbed from circulation
    2. Thyroxine (T4) released into circulation
  5. Peripheral Tissues
    1. Triiodothyronine (T3) produced from T4 deiodination
  6. Circulation
    1. Thyroid Binding Globulin (TBG) binds T4 and T3
      1. T4 is 99.96% bound
      2. T3 is 99.7% bound
    2. T4 and T3 stimulate all metabolic processes
      1. T3 is several times more potent than T4
  7. Feedback Loop
    1. Increased T4 and T3 levels suppress TRH and TSH