Which of the following disorders is related to the thyroid gland?

Graves' disease is caused due to

$I.$ Hypothyroidism causes irregularity of the menstrual cycle.
$II.$ Hyperthyroidism adversely affects body physiology.
$III.$ Hypothyroidism causes cretinism.
$IV.$ Hypothyroidism causes goitre.
Which of the above statements are correct?

The follicles of the thyroid gland are composed of which type of epithelium?

Which of the following statements is correct?

An organ $X$ has a large blood supply. It produces a hormone,the lack of which causes a disease known as cretinism. The organ is