Updated: 2/28/2020

Thyroid Hormones

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Overview
  • General
    • two forms (T3 and T4)
      • T3 is more potent than T4
      • rT3 is inactive
    • contain iodine
    • transported in blood bound to thyroxine-binding globulin (TBG) 
  • Function
    • bone growth
    • CNS maturation
      • recall cretinism involves short stature and mental retardation
    • increase the basal metabolic rate
      • via ↑ Na+/K+-ATPase activity
      • results in ↑ O2 consumption, RR, and body temperature
    • ↑ β1 receptors in heart
      • results in ↑ CO, HR, SV, and contractility
        • recall the importance of treating hyperthyroidism with β-blockers
    • ↑ glycogenolysis, gluconeogenesis, and lipolysis
  • Synthesis 
    • created in the thyroid gland
    • stored in thyroid follicles
    • thyroid peroxidase responsible for oxidation, organification, and coupling
      • forms I2 via oxidation of I-
      • forms thyroglobulin via organification of I2
    • T4 converted to T3 in peripheral tissues by outer ring deiodinase
    • T4 converted to rT3 by inner ring deiodinase
  • Regulation
    • TRH released from the hypothalamus to stimulates TSH release from the pituitary
      • TSH stimulates follicular cells to produce T3 and T4

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Questions (3)
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(M1.EC.13.84) An important step in the formation of thyroid hormones is the formation of I2 via oxidation of I-. Which of the following molecules is responsible for this reaction?

QID: 100385
1

Thyroid deiodinase

6%

(8/124)

2

Thyroid peroxidase

75%

(93/124)

3

5'-deiodinase

10%

(12/124)

4

Perchlorate

3%

(4/124)

5

Propylthiouracil

2%

(2/124)

M 1 E

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