thyroid hormone physiology Flashcards
What is the arterial supply to the thyroid
Superior thyroid artery (branch of external carotid), inferior thyroid artery (branch of the subclavian)
What is venous drainage of the thyroid
Superior thyroid vein—> Internal jugular vein
Middle—-> internal jugular vein
Inferior—-> brachiocephalic vein
What are the primary hormones produced by the thyroid
T3- tri-iodothyronine, largely produced in other tissues as well as thyroid.
T4- Thyroxine
calcitonin
What happens to T4 within tissues
In tissues, deiodinase enzymes convert T4 to T3
What are some clinical syndromes to do with the thyroid and how are they treated
Hyperthyroidism- treated with drugs or removing the thyroid, surgically or via radioactive iodine.
Hypothyroidism- treated with replacement therapy of T4
What is Levothyroxine
It is a drug used to treat thyroid deficiency and can be used to suppress TSH secretion in the treatment of some thyroid tumours.
What is carbimazole
Used to treat Hyperthyroidism- decreases T3 & T4 by converting itself to methimazole which prevents peroxidase iodinating the tyrosine residues on thyroglobulin.
Outline the physiology of Thyroid hormone production
Iodine and tyrosine make mono-iodotyrosine (MIT) and di-iodotyrosine (DIT) which join to make either T3 or T4 but T4 can make T3 in tissues via Enzymes.
What are the main effects of the thyroid hormones
mainly to increase basal metabolic rate:
- increased carb metabolism
- increased in the synthesis, mobilisation and degradation of lipids
- increased protein synthesis.
How does TSH affect the thyroid
TRH stimulates the secretion of TSH which stimulates the secretion of T3 & T4 directly and indirectly by suppressing the release of TRH.
T4—>T3 (in the liver and other tissues)
What is propylthiouracil
Used to treat hyperthyroidism (including graves disease) by inhibiting thyroperoxidase.
