The endodermal derivatives include:

Which of the following statements is correct?

On an educational trip to Uttaranchal,Ketki and her friends observe that many local people have swollen necks. Please help Ketki and her friends to find out the solutions to the following questions.
$(a)$ Which probable disease are these people suffering from?
$(b)$ How is it caused?
$(c)$ What effect does this condition have on pregnancy?

............ support the process of red blood cells formation.

$A -$ Thyroid gland secretes a protein hormone called thyrocalcitonin $(TCT)$,which regulates the blood calcium levels.
$R - TCT$ is a hypercalcemic hormone.

Goiter is caused by the abnormal functioning of which gland?