Why is thyroxine considered a hormone and not an enzyme?

What is Isthmus?

Which of the following endocrine glands stores its secretion in the extracellular space before releasing it into the blood?

Which of the following statements is correct?

Consider the following statements with respect to Calcitonin:
$I$. It is non-iodised.
$II$. It is secreted by parafollicular cells.
$III$. It regulates the calcium level in blood.
$IV$. It is also called as $TCT$ (Thyrocalcitonin).
$V$. It is a hyperglycemic agent.
Select the option containing correct statements from the above given statements.

Mention the difference between hypothyroidism and hyperthyroidism.