Bio L2 Thyroid Hormones Flashcards
What molecule inhibits iodide uptake in thyroid?
Thiocyanate
What enzyme coverts iodide to iodine?
Thyroid peroxidase (TPO)
What is organification reaction?
Iodination of tyrosine residues (at position 3 first)
What releases when 2 DIT couple
Thyroxine and alanine
TPO is inhibited by?
Methimazole & PTU
What are PD and MCT
PD: pendrin (transports iodide to colloid cavity)
MCT: mono carboxyl transporter (transports hormones into blood)
T4:T3 ratio? Which is more efficient?
30:1 , T3
What are the carriers ?
Albumin, thyroxine-binding globulin (alpha), prealbumin (only T4)
Which form affects regulation?
Free form, negative feedback inhibits TSH
What effect does T3 have on cells?
T3 receptors are in the nucleus, they stimulate metabolic activities (production of proteins)
Increases Na/K ATPase —> more ATP needed
Effects on CHO metabolism
Liver glycogenolysis, intestinal glucose absorption, potentiate epinephrine glycogenolysis effect
Effect on fat
Stimulates hormone sensitive lipase in fats, stimulates FA oxidation, reduces cholesterol as it promotes its oxidation to bile acids
Regulation of thyroid hormones
1) Hypothalamic-hypophyseal-thyroid axis
2) Auto-regulation by iodide content (low=increase sensitivity to TSH & higher T3 than T4)
3) Peripherally by hormone conversion to inactive rT3