thyroid physiology Flashcards
in embryology where does the thyroid develop
foramen caecum
when does the thyroid reach its final position and where is it (embryology)
week 7 - C5-T1
what are the stages of thyroid development
1) endothermal thickening 2) thyroglossal duct formation 3) bifurcation at lower end of thyroglossal duct 4) thyroid develops 5) isthmus forms
what nerve supplies the thyroid
valgus (CNX)
what vasculature does the thyroid have
sup/ inf thyroid arters + 3 pairs of veins
what cells is the thyroid made of
follicles surrounded by flat and cuboidal follicle cells + occasional C/ para-follicular cells (larger)
what do thyroid follicles do
convert thyroglobulin –> T3/4
what do the centre of thyroid follicles look like
pink centre and contain thyroglobulin
what do C cells contain and what do they do
calcitonin which inhibits osteoclasts and lowers calcium (opposite to PTH)
how is the thyroid controlled by negative feedback
hypothalamus secretes TRH –> ant pit secretes TSH –> thyroid secretes T3 and T4 which reduce TRH and TSH production
how does thyroid stimulating hormone (TSH) activate thyroid cells
binds to receptor cell on thyroid, Ga protein increases cAMP which increases T3/ 4
how to functional follicle cells make thyroglobulin (5)
1) iodide uptake, 2) oxidation to iodine, 3) iodination of thyroglobulin 4) formation of MIT and DIT the precursors of T3/4 5) T3/4 stored until secretion
how are T3 + 4 made from MIT and DIT
MIT (mono) + DIT (di) –> T3.
DIT + DIT –> T4
what is the most abundant thyroid hormone and what is the major active thyroid hormone
90% thyroxine (T4), triiodothyronine (T3) more potent and majorly active
where is the majority of T4 converted to T3
liver and kidney
