In countries where dietary intake of iodine is low, goitres, enlargement of the thyroid are common. What would you say about the chain of events leading to formation of goitre?
In the absence of iodine, neither thyroxine nor triiodothyronine hormone is produced, due to which their concentration in the blood decreases. To compensate this, the anterior pituitary secretes large amounts of TSH, which stimulate the growth of the thyroid gland, some times to gigantic proportions, leading to formation of goitre.
However, enlargement of the gland cannot increase production of the hormones, because of the deficiency of main ingredient, i.e., thyroxine hormone.