Q What is the constitution of the endocrine system?
The endocrine system is constituted by the hormones and the endocrine glands they secrete.
Q. What is the histological nature of the glands? How are they formed?
The glands are epithelial tissues and they are prepared of epithelium that during the embryonic development invaginated into other tissues.
In the endocrine glands the invagination is complete and there are no secretion ducts, in the exocrine glands the invagination has preserved secretion ducts.