Question

In vertebrates, chemical messengers called hormones are secreted by the _____ system. endocrine excretory hormonal pituitary

Answer 1

The correct answer should be the endocrine system.

Hormones are secreted by endocrine glands in endocrine systems. Opposite of this would be the exocrine system consisting of exocrine glands.

Answer 2

The correct answer is endocrine system.

Endocrine system in vertebrates consists of endocrine glands. Endocrine glands do not have ducts thus, they are also called as ductless glands. The glands which secretes enzymes are glands with duct, called exocrine glands.    Therefore, the hormones secreted from endocrine glands are directly poured into the blood for the action on target organs. Examples of endocrine glands are pituitary gland, thyroid gland, adrenal gland.