Why are some patients of diabetes treated by giving injections of insulin?

Name the disease caused by the deficiency of thyroxine hormone in the body.

Which halogen element is necessary for the making of thyroxine hormone by the thyroid gland?

What is the name of in-built 'arrangement' in our body which controls the timing and amount of hormones released by various endocrine glands in the body?

Name one gland each:

(a) which acts only as an endocrine gland.

. (b) which acts only as an exocrine gland.

(c) which acts both as an endocrine gland as well as an exocrine gland.