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Endocrinology Part I
What is the function of the thyroid organ?
regulate body's metabolism
What thyroid hormone does the thyroid produce?
1) Thyroxine (t4)
2) thriiodothyronine (t3)
What initiates T3 and t4 secretion
What does hypothalamus secrete
What does TRH act on?
What does Anterior pituitary secrete?
What does TSH act on?
TSH can negatively inhibit what?
What does TRH stand for?
What does TSH stand for?
thyroid stimulating hormone
T4 is solely produced by
80% of t3 is formed from?
20-25% of t3 is made from?
Which is more metabolically active? T3 or t4
T3 and t4 is bound to what protein?
TBG (thyroxine-binding globulin)
Free fraction of t4 and t3 is what?
metabolically active component
What is hypothyroidism?
deficiency of thyroid hormone
What causes hypothyroidism?
1)Primary: failure of thyroid to produce thyroid hormone
2)Secondary: failure of anterior pituitary to secrete TSH
3)Tertiary: failure of hypothalamus to produce TRH
What is hyperthyroidism?
excessive thyroid hormone
free T4 is also called what?
What does free thyroxine represent?
level or hormone available for uptake and use by cell
What is free thyroxine used in conjunction with?
What does total T4 measure?
amount of t4 in blood, both bound and free t4
What is total t4 influenced by?
concentration or binding affinity of thyroid binding protein
Whats an alternative way to measure total t4?
obtain t3 resin uptake test
What is t3 used as an indicator for?
hyperthyroidism (not reliable for hypothyroidism)
almost all of t3 is ____ bound
What is T3RU
Serum triiodothyronine Resin uptake
T3RU estimates the number of binding sites on thyroid binding protein by binding to ___
If T3RU value is high it indicates
low thyroid binding protein
if T3RU value is low it indicates
high thyroid binding protein
T3RU is used to calculate the free ___ index
Whats the formula for Free t4 index?
Free T4 index = (total serum T4 in mg/dL)*(T3 resin uptake in %)
What does free t4 index tell you?
how much t4 is present compared to thyroxine binding globulin
Rise in TSH is usually first sign of
TSH is used to adjust dosage of
levothyroxine replacement therapy
how many weeks do you need to wait after starting/changing therapy to assess TSH
TRH measures what?
ability of exogenous TRH to stimulate pituitary to release TSH
TRH given IV with TSH levels drawn at basedline and __-__ minutes
What does radioactive iodine uptake test determine?
if gland is functionally normal
if there is high uptake in radioactive iodine uptake test you have
If there is low uptake in radioactive iodine uptake test you have
Antithyroid antibodies > 1:1000 indicates
Hashimoto's thyroiditis or grave's disease
How is TSH used in Lab test?
identify problems with pituitary
How is TRH used in lab test?
used to differentiate secondary from tertiary hypothyrodism
How is Free T4 used in lab test?
used with TSH to determine thyroid functioning
How is T4 used in lab test?
used with TSH to confirm thyroid failure
How is t3 uptake resin used in lab?
helps measure t4 and estimate unoccupied serum protein sites
How is T3 used in lab?
used to diagnose hyperthyroidism
How is free t4 index used?
indicator of thyroid status in presence of abnormalities in plasma protein binding
Mild hypothyroidism is indicated by
increase TSH, t3 and t4 ---
hypothyroidism is indicated by
t3 and t4 decrease, increase TSH
mild hyperthyroidism is indicated by
t3 and t4 ----, TSH is decrease
hyperthyroidism is indicated by
t3 and t4 increase, TSH decrease
In primary hypothyrodism TSH before TRH stim ___, TSH after TRH stim ___
increase, exaggerated TSH response
In secondary hypothyrodism TSH before TRH stim ___, TSH after TRH stim ___
decrease, no tsh response
In tertiary hypothyrodism TSH before TRH stim ___, TSH after TRH stim ___
decrease, sluggish tsh response
Whats lab values for free T4?
.8 to 1.5 ng/dl
Whats the lab values for total T4?
4 TO 12.5 ng/dl
lab value Serum t3 resin reuptake
lab value for free t4 index
lab value for t3
78-195 ng/dl or 1.2-3nmol/L
lab value for TSH
lab value for radioactive iodine uptake test
12-20% uptake at 6hr