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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

Hypothalamus

What does hypothalamus secrete

TRH

What does TRH act on?

Anterior Pituitary

What does Anterior pituitary secrete?

TSH

What does TSH act on?

Thyroid

TSH can negatively inhibit what?

hypothalamus

What does TRH stand for?

thyrotropin-releasing hormone

What does TSH stand for?

thyroid stimulating hormone

T4 is solely produced by

thyroid

80% of t3 is formed from?

t4

20-25% of t3 is made from?

thyroid

Which is more metabolically active? T3 or t4

T3

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?

free thyroxine

What does free thyroxine represent?

level or hormone available for uptake and use by cell

What is free thyroxine used in conjunction with?

TSH

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

protein

What is T3RU

Serum triiodothyronine Resin uptake

T3RU estimates the number of binding sites on thyroid binding protein by binding to ___

t3

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

t4

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

thyroid failure

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

6-8 weeks

TRH measures what?

ability of exogenous TRH to stimulate pituitary to release TSH

TRH given IV with TSH levels drawn at basedline and __-__ minutes

30-60 min

What does radioactive iodine uptake test determine?

if gland is functionally normal

if there is high uptake in radioactive iodine uptake test you have

hyperthyrodism

If there is low uptake in radioactive iodine uptake test you have

hypothyrodism

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

25-34%

lab value for t3

78-195 ng/dl or 1.2-3nmol/L

lab value for TSH

.25-6.7 uu/ml

lab value for radioactive iodine uptake test

12-20% uptake at 6hr

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