PHYSIOLOGY

Question 1

SYNTHESIS OF THYROXINE

Answer 1

Trapping of inorganic iodide from blood , oxidation to iodine , binding of iodine with tyrosine to iodo tyrosine , coupling of mono iodotyrosine and diiodo tyrosine to form T3 , T4

Question 2

T3 & T4 BOUND

Answer 2

They are bound to thyroglobulin inside the colloid in follicles. in blood they are bound by ALBUMIN , THYROXINE BINDING GLOBULIN , THYROXINE BINDING PRE ALBUMIN.

Question 3

T3

Answer 3

0.3% OF THE TOTAL CIRCULATING HORMONE
PRODUCED IN PERIPHERY
QUICK ACTING (WITHIN A FEW HOURS)

Question 4

T4

Answer 4

0.03% of the total thyroid hormones.
acts slowly ( 4-14 days)

Question 5

TSH origin and regulation

Answer 5

from anterior pituitary
negative feedbavk of thyroxine and thyrotrophin releasing hormone from hypothalamus

Question 6

thyroid stimulating antibodies TRAbs

Answer 6

more protracted action on TSH receptors of the follicles than TSH (16-24 vs 1.5-3 hours) . serum concentrations are very low but not essential to make a diagnosis

Question 7

THYROID AUTO ANTIBODIES

Answer 7

TPO > 25 units / ml
antithyroglobulin > 1:1000 titres are significant.
seronegative autoimmune thyroiditis can also occur.

Question 8

tumour markers for medullary carcinoma thyroid

Answer 8

calcitonin , CEA

Question 9

daily requirement of iodine

Answer 9

100-150mg

Question 10

anti thyroid drugs MOA

Answer 10

THYOCYANATES & PERCHLORATES Iinterfere with iodide trapping
CARBIMAZOLE & THIOURACIL interfere with oxidation of iodide and binding of iodine to tyrosine