4 - Thyroid Intro

Question 1

embyro origins of medial and lateral thyroid

Answer 1

medial - foramen cecum at base of tongue

lateral - ultimobranchial body - part of 5th branchial arch

Question 2

rate limiting step for thyroid hormone synth, and what is it regulated by

Answer 2

iodide entrapment by Na-I symporter

regulated by TSH

Question 3

which amino acid is thyroid hormone based on?

Answer 3

tyrosine

Question 4

what do thyroid hormones bind to in serum?

Answer 4

albumin (15%)
thyroid binding globulin (70%)
transthyretin (10%)

Question 5

what lab test tells you the pt’s true metabolic (thyroid) state?

Answer 5

free T4

Question 6

causes of inc and dec thryoid binding globulin

Answer 6

inc - high estrogen states (pregnancy), liver dz (early)

dec - androgens / anabolic states, liver dz (late)

Question 7

T3 resin uptake test

Answer 7

used to determine amt of binding proteins
mix serum w/ radioactive T3 and let equilibrate
the resin gets the remaining tracer
if the resin has high uptake of tracer, that means there is low binding globulin, and vice versa

Question 8

which thyroid molecule is inc in all thyroid disease?

Answer 8

thyroglobulin

Question 9

what is the only thing thyroglobulin monitoring is useful for?

Answer 9

thyroid cancer surveillance after surg/ablation

Question 10

RAIU - what is it and what do results tell you

Answer 10

thyroid uptake scan
given radioactive iodide then scanned to see how much thyroid took
“hot” thyroid indicates hyperthyroid
“cold” defect suspicious for malignancy

Question 11

dz with low RAIU and hyperthyroid sx

Answer 11

thyroiditis
hormone ingestion (thyrotoxicosis)