Metabolism & Secretion Thyroid Cont'd

Question 1

How many days does T4 is synthesized?

Answer 1

from direct TG secretion
(6-7 days)

Question 2

Where does most Plasma T3 derived?

Answer 2

• Extra-thyroidal deiodination
• Liver/kidney
• Peripheral tissues

Question 3

T4 accounts 80% of plasma T3

Answer 3

Extra-thyroidal deiodination

Question 4

deiodinate T4

Answer 4

Liver/kidney

Question 5

Peripheral tissue

Answer 5

T4 → T3/rT3

Question 6

more active

Answer 6

T3

Question 7

inactive

Answer 7

rT3

Question 8

TRUE or FALSE: T3 test is useful in diagnosing hypothyroidism

Answer 8

FALSE; it is not useful in diagnosing hypothyroidism because levels
are not reduced until it becomes severe

Question 9

Enumerate three process from which TH is metabolized:

Answer 9

– deiodination, deamination, conjugation (by glucuronic acid)

Question 10

complete the process below:

Conjugated → ________ → Intestine → ________

Answer 10

Conjugated → Bile duct → Intestine → excreted

Question 11

Give what is/are asked:

What is/are inhibitory substances for TH synthesis:

Answer 11

• Glucocorticoids
• Dopamine
• Propanolol
• Lithium

Question 12

inhibits TSH → decrease T4 and T3

Answer 12

Glucocorticoids’

Question 13

inhibits TSH

Answer 13

Dopamine

Question 14

inhibit conversion of T4 to T3

Answer 14

Propanolol

Question 15

alter Tg structure, inhibit iodotyrosine coupling, inhibit thyroid hormones

Answer 15

Lithium

Question 16

it is considered aas the 3rd most circulating thyroid hormone

Answer 16

rT3

Question 17

what does the rT3 remove?

Answer 17

it removes 1 iodine from the inner ring of T4

Question 18

Discuss the Hypothalamic-pituitary-thyroid axis

Answer 18

Low TH = increase TRH & TSH

-Increase T3, T4 = decrease TRH & TSH

Question 19

Half-life of T4 metabolism

Answer 19

4 hours

Question 19

rT3 is elevated in which condition?

Answer 19

rT3 is elevated in patients with euthyroid sick syndrome

it is used to assess borderline or conflicting laboratory results

Question 20

enumerate the 4 isoforms of T3 receptors:

Answer 20

α1 – present in most tissues
α2 – inhibitory of thyroid hormones
β1 – works with α1
β2 – in pituitary, for negative feedback

Question 21

Serum iodide

Answer 21

High = transport inhibited, high DIT, T4
Low = more absorbed, high MIT, T3

Question 22

other name for Triidothyronine (T3)

Answer 22

3, 5, 3’ TriIodothyronine

Question 23

TRUE or FALSE: T4 it has the most hormonal activity

Answer 23

FALSE: it is T3

Question 24

TRUE or FALSE: T3 indicator of recovery or recurrence of hyperthyroidism

Answer 24

TRUE

Question 25

TRUE or FALSE: T4 is 1st seen in hyperthyroidism

Answer 25

FALSE; it is T3

Question 26

How do we measure T3 levels?

Answer 26

via competitive immunoassay

Question 27

What is the physiologically active form of T3?

Answer 27

FT3

Question 28

what is the other name for Tetraiodothyronine (T4)

Answer 28

“3,5, 3’, 5’ Tetraiodothyronine” “Thyroxine”

Question 29

TRUE or FALSE: T4 is the principal secretory product

Answer 29

TRUE

Question 30

TRUE or FALSE: T3 is the MAJOR fraction of Organic iodine Prohormone of T3

Answer 30

FALSE; it is T4

Question 31

it is and indicator for thyroid secretory rate

Answer 31

increase T4

Question 32

How do we measure T4 levels?

Answer 32

Immunoassay after hormone separated from protein

Question 33

Physiologically active form of T4

Answer 33

FT4

Question 34

conversion factor for T4

Answer 34

12.9

Question 35

these are agents that causes goiter, increases TSH

Answer 35

Goitrogens

Question 36

a type of Goiter that does not define functional state

Answer 36

Thyromegaly

Question 37

Enumerate the types of Thyromegaly

Answer 37

- Hyperthyroidism (Toxic) - Hypothyroidism (non-toxic) - Euthyroid (Non-toxic)

Question 38

Classifications of goiter: Stage 0 Stage 1a Stage 1b Stage 2 Stage 3

Answer 38

- No! – palpable, not visible – palpable, visible if neck is extended – visible (even neck not extended) – very large

Question 39

- Most important test for thyroid function monitoring - Used for monitoring and to adjust thyroid hormone replacement therapy

Answer 39

Thyroid Stimulating Hormone determination:

Question 40

Good for differentiating Primary hypothyroidism and Secondary hypothyroidism and also best for detection of primary thyroid disorder

Answer 40

Thyroid Stimulating Hormone determination:

Question 41

Used as marker for Thyroid cancer (post-operative or monitoring metastatic/recurrence)

Answer 41

Thyroglobulin test

Question 42

what does thyroglobulin differentiates?

Answer 42

sub-acute thyroiditis (high) from thyrotoxicosis factitia (low)

Question 43

These are the lab methods employed for Thyroglobulin tests

Answer 43

- ELISA, - RIA, - IRMA, =Immunochemiluminescent assay

Question 44

enumerate the conditions for Thyroglobulin test: Increase: Decrease:

Answer 44

- Thyroid cancer - Nodular goiter - Hypothyroidism - goiterous hypothyroidism - thyrotoxicosis factitia