Thyroid (Welch) Flashcards
Thyroid hormones are derivates of what amino acid?
Tyrosine
How are thyroid hormones named?
Based off number of iodines tyrosine has attached
MIT=monoiodotyrosine
DIT=diiodotyrosine
What makes up Triiodotyrosine?
MIT + DIT = T3
What makes up T4?
DIT + DIT = T4
What are the active binders to the thyroid receptors?
T3 and T4
What is key for the creation of MIT and DIT?
Iodide from the diet
What is the stimulus for the uptake of iodide by the cells of the thyroid?
Thyroid stimulating hormone (TSH) from anterior pituitary
When TSH binds to the membrane of the thyroid cell what is required for the uptake of the iodide?
Energy via N/K ATPase pump
When TSH binds to the membrane of the thyroid cell, what is required for the uptake of the iodide?
Energy via N/K ATPase pupm
What is the character of MIT and DIT and what do they require?
Unstable. Require binding to thyroglobulin to stabilize in the thyroid
What happens if you don’t have enough thyroglobulin?
MIT and DIT will not stabilize and therefore will not get TC and T4
What are the reactions that Thyroidal Peroxidase catalyzes in the production of T3 and T4?
- Change taken up iodide into iodine
- Binding of MIT and DIT to thyroglobulin to stabilize
- Binding of MIT and DIT to create T3 and T4
Peroxidase is activated by what?
TSH
What things does TSh stimulate in the production of T3 and T4?
- Iodide uptake
- Peroxidase action
- Activate adenyllate cyclase
- Activate lysosome droplet to release T3 and T4
What is Thyroid Colloid?
Protein and fat storage area with no enzymes to store and protect T3 and T4
What does the increase in Adenylate Cyclase by TSH stimulation cause?
Increase in cAMP which causes lysosome to destroy colloid and release the stored T3 and T4
What causes the release of TSH from the anterior pituitary?
Thyrotropic releasing hormone by hypothalamus
What inhibits both TRH from Hypothalamus and TSH from the anterior pituitary?
T3 and T4
What is assumed to be the cause of any thyroid problem until proven otherwise?
TSH (anterior pituitary) is the cause
What does TRH from the hypothalamus cause the release of?
TSH, Prolactin, and GH
What is the diagnostic use of TRH (Protirelin)?
Administer and measure TSH and Thyroid hormones
What is the characteristic of a primary defect upon administration of TRH?
TSH increases but T4 level remains the same
What is the characteristic of a secondary defect upon administration of TRH?
TSH does not increase
What is the characteristic of a secondary defect upon administration of TRH?
Both TSh and T4 increase
What is the drug of choice for determining where breakdown lies in the excretion of thyroid hormones?
Protirelin
If protirelin (synthetic TRH) given and there is no change in TSH or T3 and T4k where is the problem?
PItuitary defect
If protirelin (synthetic TRH) is given to a hypothalamic patient and TSH increases, but T3 and T4 do not change, where is the problem?
At level of thyroid
If protirelin (synthetic TRH) is given to hypothalamic patient and TSH increases and T3 and T4 increase, where is the problem?
At the level of the hypothalamus
Of the thyroid problem levels, which is the most difficult to treat?
The hypothalamus-level problem because it is inside the blood-brain barrier
Which is the larger molecule: TRH or TSH?
TSH (large glycopeptides)
TRH (small tripeptide)
TSH deficiency leads to what physical change in thyroid?
Atrophy
TSH excess leads to what physical change in thyroid?
Goiter (hypervascular, hypertrophic, hyperplastic)
What is a synthetic TSH used diagnostically to distinguish between hypopituitarism and primary hypothyroidism?
Thytropar
What must be used in conjunction with Thytropar for diagnosis and what is the contraindication?
Used with radioactive iodine 131-I
Contraindicated in pregnant women
If there are small quantities in the thyroid of the radioactive iodine after it has been administered in conjunction with the Thytropar (diagnostic TSH) where does the problem lie?
Abnormal thyroid
What are 3 places a high iodine concentration will shut down a thyroid cell?
- Poison the N/K ATPase pump stopping iodine uptake
- Inhibit peroxidase action
- Inhibit adenylate cyclase
What ist he name of the high iodine solution used prior to surgery to shut down the thyroid in order to avoid a dump to T3 and T4?
Lugall’s solution
Why is T3 more active than T4?
Less protein-bound, faster onset, 4 times more potent
Ten times greater receptor affinity
When would T3 be administered therapeutically?
In ER if euthyroidal
What is a stabilized euthyroidal patient given?
T4
Where is T4 converted to T3?
In liver by deiodinase enzymes
What percent of all T4 that is made is converted into T3 in the liver?
20%