Thyroid Flashcards
what does the thyroid gland regulate
tissue metabolism and growth and development
what are the thyroid hormones
T3 and T4
where are t3 and t4 sythesized, and stored
synthesized in the follicular cells of the thyroid and stored in iodinated thyroglobulin in extracellular colloid compartment
how does iodine relate to t3 and t4
it is enesential for t3 and t4 synthesis
by what hypothalamus and pituitary hormone is the thyroid stimulated and regulated by
TRH and TSH (thyroptropin)
- there is feedback regulation of TSH and TRH by t3 and t4
which thyroid cells secrete calcitonin
C cells
what is the active throid hormone how does it occur
t4 is deiodinized into t3 ( active)
what is the steady state level of iodine in the body where is the majority located, whats the percentage
20-50mg , large proportion (25%) is in the thyroid
what form is unincorporated iodine in?
in the form of iodide (I-) not iodine (I2)
what is the daily need of iodine
150ug
how much iodine does the thyroid use? what is the majority used for
the thyroid gland uses 120ug a day, mostly for the synthesis of t3 and t4
what happens to iodine when there is thyroid hormone degredation?
iodine and iodide are unused and are excreted through the urine
what does iodine insuffiecent cause
hypothyroidism
what are the steps in the synthesis and release of thyroid hormones (7)
1) active transport of iodide by follicular cells
2) synthesis and internal secretion tyrosine containing precursor protein (thyroglobulin) in the colloid
3) iodiniation of thyroglobulin tyrosine residues within the colloid
4) coupling of 2 iodotyrosine residues of thyroglobulin
5) cellular uptake of iodinated thyroglobulin by reabsorption from the colloid
6) proteolytic release of iodinated thryronines in the lysozymes
7) release of t3 and t4 into the blood
- how does iodine accumulate in follicular cells of the thyroid
- what type of transport is this
- through a I-/Na symport
- secondary active transport
how does iodine get from the follicular cell to the colloid
via facilitated diffusion
what is thyrogloblulin
protein precursor that contains tyrosine residues used to to synthesize t3 and t4
where is thyroblobulin secreted
in the ER of follicular cells
what is thyroglobulin secreted in to the colloid with, what is its function?
with thyroid peroxidase ( TPO) catalyzes its iodination
what is the function of tpo
catalyzes the oxidation of iodide to iodine and its binding to tyrosine on thyroglobulin
what are the 2 steps of the iodiniation of thyroglobulin
first step yields 3-monoiodotyrosine (MIT) and then 3,5 diodotyrosine (DIT)
what is the coupling of the 2 iodotyrosine residues catalysed by
TPO ( thyroid peroxidase)