Thyroid notes

Question 1

the thyroid gland consists of

Answer 1

two lobes connected by the isthmus and is located just below the cricoid cartilage

Question 2

thyroid enlargement/goiter usually extends

Answer 2

posteriorly and inferiorly

Question 3

formation for thyroid hormones is dependent on

Answer 3

iodine

Question 4

sources of dietary iodine

Answer 4

ionized salt, seafood, dairy products, meat, vegetables, and eggs

Question 5

after iodine is absorbed into the GI tract

Answer 5

there is an active transport of iodide into the thyroid cell via Na+/I- symporter

Question 6

iodide is oxidized into

Answer 6

iodide in thyroglobulin via thyroid peroxidase

Question 7

iodine and tyrosine combine to form

Answer 7

monoiodotyrosine (MIT) and diiodotyrosine (DIT) - also catalyzed by TPO

Question 8

MIT + DIT =

Answer 8

T3

Question 9

DIT + DIT =

Answer 9

T4

Question 10

iodide deficiency increases

Answer 10

ratio of MIT to DIT

Question 11

when ratio of MIT and DIT increases

Answer 11

the ratio of T3 to T4, decreasing secretion of T4, and increasing serum TSH

Question 12

proteolysis of thyroglobulin results in

Answer 12

the release of T3, T4, and iodotyrosines

Question 13

proteolysis of thyroglobulin can be inhibited by

Answer 13

excess iodide and lithium

Question 14

carrier proteins of thyroid hormones

Answer 14

1) thyroxine-binding globulin (TBG)
2) thyroxine-binding prealbumin (TBPA)
3) albumin

Question 15

are unbound or bound fraction responsible for hormonal activity

Answer 15

the unbound or “free”

Question 16

percentage of T3 bound

Answer 16

99.5% bound

Question 17

percentage of T4 bound

Answer 17

99.96% bound

Question 18

amount of T4 secreted from thyroid

Answer 18

80 ug

Question 19

amount of T3 secreted from thyroid

Answer 19

30 ug

Question 20

percent of T4 secreted from thyroid

Answer 20

100%

Question 21

percent of T3 secreted from thyroid

Answer 21

20%

Question 22

half-life of T4

Answer 22

7 days

Question 23

half-life of T3

Answer 23

1 day

Question 24

thyrotopin-releasing hormone is released from

Answer 24

the hypothalamus

Question 25

TRH stimulates

Answer 25

synthesis and release of TSH and prolactin

Question 26

TRH secretion stimulated by

Answer 26

decreased serum T3 or T4

Question 27

TRH secretion blocked by

Answer 27

increased serum T3 or T4

Question 28

TSH is released from

Answer 28

the pituitary

Question 29

TSH synthesis is controlled by

Answer 29

level of T3 or T4 and TRH

Question 30

drugs that inhibit TSH

Answer 30

somatostatin, dopamine, dopamine agonists, and steroids

Question 31

conversion of T4 to T3 in peripheral tissues via

Answer 31

5’ deiodinase

Question 32

TSH test is recommended for

Answer 32

initial evaluation of thyroid function

Question 33

TSH is most sensitive in

Answer 33

hyper, hypo, and replacement therapy

Question 34

Total T4

Answer 34

total free and bound T4, specific and sensitive test if no alterations in TBG

Question 35

Total T3

Answer 35

total free and bound T3, used to detect early hyperthyroidism and T3 toxicosis

Question 36

Free T4

Answer 36

direct measurement of free thyroxine, “gold standard” by equilibrium dialysis technique

Question 37

Free T4 index

Answer 37

compensates for alterations in TBG by using T3 resin-uptake, may not be valid in patients with euthyroid sick syndrome

Question 38

Radioactive Iodine Uptake

Answer 38

assesses gland’s use of iodine after trace doses of I1213 or I131, does not provide info regarding hormone synthesis

Question 39

RAI-U can be falsely decreased in

Answer 39

patients with excess iodide intake

Question 40

RAI-U is elevated in

Answer 40

hyperthyroidism

Question 41

Thyroid scan test

Answer 41

trace doses of I123 or I131 given prior scan

Question 42

Thyroid scan is able to assess

Answer 42

gland size, shape, and tissue activity

Question 43

Thyroid scan is able to detect

Answer 43

hot or cold areas in nodular disease