Thyroid Flashcards
Iodide Trap
Iodide is cotransported with Na into follicular cell on
basolateral side
TH Synth
Iodide incorp on tyrosines on TG via thyroperoxidase = monoiodotyrosine & diiodotyrosine (organification)
2DITs = T4
1DIT + 1 MIT = T3
Combine by thyroperoxidase
Thyronine
TH backbone
T3
Active. 1 day = half life. 10x higher affinity by receptor.
TH Secretion
TG endocytosed into follicular. Lysosomal enzyme cleave T4 & T3 from TG
Then secreted
T4
Half life = 7 days
Aka tyroxine
To T3 by 5’deiodinase
TH actions
Main regulator metabolic rate
Necessary for normal fetal development
Enhances response to catecholamines
TH Regulation
Hypothalmus TRH -> ant. pituitary -> TSH -> stim iodide pump, thyroperoxidase, & endocytosis = more TH synth
T3 & T4 inhibit TRH
Graves’ Disease
Most common hyperthyroid Ab to TSH receptor - activating Pretibial Myxedema, exophthalmos, lid retraction Low/normal TSH High T4 High RAI
Toxic Nodule Goiter
Mutation of TSH receptor to be constitutively active
Low TSH
High T4
High RAI
Thyroiditis
Viral Inf = leaky memb
Low TSH
High T4
Low RAI
TSHoma
produces TSH
High TSH
High T4 & T3
High RAI
Thyroid Hormone Resistance
Receptor mutation. Low metab, ‘bird-lik’face
High TSH
High T4
High RAI
Congenital Hypothyroid
2:1 females Usually appears normal then Large posterior fontanel o Prolonged jaundice o Macroglossia o Hoarse cry o Umbilical hernia o Hypotonia Low T4, high TSH
Central Hypothyroidism
Def in hypothal or pituitary
Low TH
Normal TSH
Low FT4
