Iodine deficiency causes:

Iodine is associated with which of the following hormones?

Read the given statements $:$
$(A)$ Hypothyroidism during pregnancy causes defective development and maturation of the growing baby.
$(B)$ Thyroxine does not require a secondary messenger.
$(C)$ Thyroxine plays a major role in the regulation of Basal Metabolic Rate $(BMR)$.
$(D)$ Hypersecretion of thyroxine could cause immunodeficiency.
How many of the above statements are correct?

What is Isthmus?

If the thyroid gland is completely removed from a tadpole,then :-

'Exophthalmic goitre' $(Grave's\,disease)$ is caused due to