This Viva will test your knowledge of the endocrinology of the thyroid gland. 
Q 1 What is a hormone? How is it defined? 
Subsequent questions asked about chemical types of hormones, hormones secreted by the 
anterior pituitary, the principal biological role of the thyroid hormones, production of thyroid 
hormones, advantages of thyroxine for thyroid replacement in comparison to triiodothyronine, 
and mechanism of action of propylthiouracil.