Metabolism & Secretion Thyroid Cont'd Flashcards
How many days does T4 is synthesized?
from direct TG secretion
(6-7 days)
Where does most Plasma T3 derived?
- Extra-thyroidal deiodination
- Liver/kidney
- Peripheral tissues
T4 accounts 80% of plasma T3
Extra-thyroidal deiodination
deiodinate T4
Liver/kidney
Peripheral tissue
T4 → T3/rT3
more active
T3
inactive
rT3
TRUE or FALSE: T3 test is useful in diagnosing hypothyroidism
FALSE; it is not useful in diagnosing hypothyroidism because levels
are not reduced until it becomes severe
Enumerate three process from which TH is metabolized:
– deiodination, deamination, conjugation (by glucuronic acid)
complete the process below:
Conjugated → ________ → Intestine → ________
Conjugated → Bile duct → Intestine → excreted
Give what is/are asked:
What is/are inhibitory substances for TH synthesis:
- Glucocorticoids
- Dopamine
- Propanolol
- Lithium
inhibits TSH → decrease T4 and T3
Glucocorticoids’
inhibits TSH
Dopamine
inhibit conversion of T4 to T3
Propanolol
alter Tg structure, inhibit iodotyrosine coupling, inhibit thyroid hormones
Lithium
it is considered aas the 3rd most circulating thyroid hormone
rT3
what does the rT3 remove?
it removes 1 iodine from the inner ring of T4
Discuss the Hypothalamic-pituitary-thyroid axis
Low TH = increase TRH & TSH
-Increase T3, T4 = decrease TRH & TSH
Half-life of T4 metabolism
4 hours
rT3 is elevated in which condition?
rT3 is elevated in patients with euthyroid sick syndrome
it is used to assess borderline or conflicting laboratory results
enumerate the 4 isoforms of T3 receptors:
α1 – present in most tissues
α2 – inhibitory of thyroid hormones
β1 – works with α1
β2 – in pituitary, for negative feedback
Serum iodide
High = transport inhibited, high DIT, T4
Low = more absorbed, high MIT, T3
other name for Triidothyronine (T3)
3, 5, 3’ TriIodothyronine
TRUE or FALSE: T4 it has the most hormonal activity
FALSE: it is T3
TRUE or FALSE: T3 indicator of recovery or recurrence of hyperthyroidism
TRUE
TRUE or FALSE: T4 is 1st seen in hyperthyroidism
FALSE; it is T3
How do we measure T3 levels?
via competitive immunoassay
What is the physiologically active form of T3?
FT3
what is the other name for Tetraiodothyronine (T4)
“3,5, 3’, 5’ Tetraiodothyronine”
“Thyroxine”
TRUE or FALSE: T4 is the principal secretory product
TRUE
TRUE or FALSE: T3 is the MAJOR fraction of Organic iodine Prohormone of T3
FALSE; it is T4
it is and indicator for thyroid secretory rate
increase T4
How do we measure T4 levels?
Immunoassay after hormone separated from protein
Physiologically active form of T4
FT4
conversion factor for T4
12.9
these are agents that causes goiter, increases TSH
Goitrogens
a type of Goiter that does not define functional state
Thyromegaly
Enumerate the types of Thyromegaly
- Hyperthyroidism (Toxic)
- Hypothyroidism (non-toxic)
- Euthyroid (Non-toxic)
Classifications of goiter:
Stage 0
Stage 1a
Stage 1b
Stage 2
Stage 3
- No!
– palpable, not visible
– palpable, visible if neck is extended
– visible (even neck not extended)
– very large
- Most important test for thyroid function monitoring
- Used for monitoring and to adjust thyroid hormone replacement therapy
Thyroid Stimulating Hormone determination:
Good for differentiating Primary hypothyroidism and Secondary hypothyroidism and also best for detection of
primary thyroid disorder
Thyroid Stimulating Hormone determination:
Used as marker for Thyroid cancer (post-operative or monitoring metastatic/recurrence)
Thyroglobulin test
what does thyroglobulin differentiates?
sub-acute thyroiditis (high) from thyrotoxicosis factitia (low)
These are the lab methods employed for Thyroglobulin tests
- ELISA,
- RIA,
- IRMA,
=Immunochemiluminescent assay
enumerate the conditions for Thyroglobulin test:
Increase:
Decrease:
- Thyroid cancer
- Nodular goiter
- Hypothyroidism
- goiterous hypothyroidism
- thyrotoxicosis factitia
