Thyroid axis
8 important questions on Thyroid axis
What are the main components of the thyroid axis?
AP: TSH
Endocrine targets: thyroid glands, thyroid hormones (T4, T3)
Non endocrine targets: many tissues
How are thyroid hormones produced?
2. TPO catalyzes iodination of a tyrosine residue on thyroglobulins, one residue at a time
- One iodine + one tyrosine residue = Monoiodotyrosine (MIT)
- Two iodine + one tyrosine residue = diiodotyrosine (DIT)
3. TPO causes condensation of MIT and DIT residues
- T3 = triiodothyronine
- T4 = thyroxine/tetraiodothyronine
What happens in the thyroid gland when TSH stimulates it?
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What are the effects of thyroid hormones in the organism?
- Thermogenesis
- Increases GH and glucocorticoids
- Cardiac function
- Lipolysis
- Bone and muscle growth
How can we diagnose euthyroid sick syndrome?
What can cause euthyroid sick syndrome?
- Altered transport of T4
- Altered conversion of T4 to T3 due to impaired deiodinase
What are the steps to diagnosing thyroid disorders?
2. CBC and thyroid hormone panel (total T4, T3, free T4, T3, TSH, presence of thyroglobulin auto-antibodies)
3. Imaging/biopsy of thyroid tissue
4. TRH/TSH stimulation test to differentiate between primary and secondary
5. Differentials: ESS, adrenal hyperfunction
How can we treat thyroid disorders?
- Hyperthyroidism: radioactive iodine (I131), thyroidectomy, methimazole with rechecks, nutritional changes (iodine deficient diets)
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