71).THYROID HORMONES

[Editor]

a) T3 is mostly protein bound
b) protein bound iodine is a useful measure of thyroxine levels
c) carbimazole may cause a goitre
d) are steroids
e) are regulated by a positive feedback mechanism

[Editor]

tftff

T3 and T4 are both >99% bound to plasma proteins including thyroxine-binding globulin and albumin. Total T4 is a measure of thyroxine in plasma and includes free and bound hormone. However, only the free hormone (about 0.05% of the total) is biologically active. Total thyroxine may be low but the free, active component normal so the level of free hormone is a more useful measure of thyroxine levels. The thyroid hormones are iodine containing amino acids. They are regulated by a negative feedback mechanism.
Carbimazole is a thioureylene anti-thyroid drug that inhibits the iodination of thyroglobulin bound tyrosine.