Thyroid Hormone Physiology Flashcards
Blood supply to thyroid?
Superior thyroid from external carotid artery.
Inferior thyroid branch of subclavian artery.
Thyroidea ima artery, branch of arch or brachiocephalic trunk
Venous drainage of thyroids?
Superior thyroid, middle thyroid vein and inferior thyroid vein. Superior and middle from internal jugular vein and inferior from innominate veins
How does lymph drainage?
Prelaryngeal and pretracheal, deep cervical supraclavicular, and mediastinal lymph nodes
What is the major problem with thyroid surgery?
You could cause damage to recurrent laryngeal nerve
Where does recurrent laryngeal nerve do loop?
Right loops under subclavian artery and left under arch of aorta
What is thyroid made of?
Follicles-mono layer of epithelial cells enclosing a large core of viscous homogenous colloid (reserve of thyroid hormone).
Thyroid hormones?
T3, t4 and calcitonin
After halogenase frees iodide from MIT and DIT what happens?
It is reutilised by combining with thyroglobulin
How much thyroid hormone leaves gland?
95% in t4 form
Which hormone is more active?
T3 is 40x more active than T4
Which enzyme converts t4 to t3?
Deiodinase
What makes calcitonin?
Parafollicular c cells
How much t4 is converted to reverse t3?
20%
Plasma half life?
6-8 days for T4
And 1 day for T3
Circulating thyroid hormones?
Thyroxine binding globulin T4, thyroxine binding albumin T3 and thyroxine binding prealbumin
What does median eminence release?
Small peptides and dopamine
How is t4 and t3 excreted?
Conjugated and excreted in bile
Myxedema signs?
Relative obesity and stature. Lots of blubber, looks dopey
Derbyshire neck due to?
Enlarged goitre- Places far away from sea, require iodine.
Hyperthyroidism treatment?
Carbimazole,propythiouracil, thyroid surgery, radioactive iodine
Hypothyroidism treatment?
Replacement therapy T4
Core drug to treat thyroid deficiency?
Levothyroxine
Oral bioavailability- 100%
Half life - 7 days
Excretion- 20-40% in urine
At excessive doses you will get palpitations, arrhythmia, diarrhoea, insomnia, tremor, weight loss
Can be used to suppress TSH secretion in the treatment of some thyroid tumours
Core drug for hyperthyroidism?
Carbimazole:
After absorption converted to methimazole. Prevents peroxidase iodinating the thyrpglobulin, so less t3 and t4
over 90% oral bioavailability
Half life 6.4 hours
Excretion-90% in urine as metabolites
Adverse effects - rashes priorities, neutropenia, agranulocytosis
Carbimazole rare side effect?
Neutropenia and agranulocytosis
Common-pruritis and rashes
