Provide information about endocrine glands and hormones.

(N/A) Endocrine glands are ductless glands,and their secretions are called hormones.
The classical definition of a hormone is that they are produced by endocrine glands,released into the blood,and transported to a distantly located target organ.
The current scientific definition is as follows: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
This new definition covers a number of new molecules in addition to the hormones secreted by the organized endocrine glands.
Invertebrates possess very simple endocrine systems with few hormones,whereas a large number of chemicals act as hormones and provide coordination in vertebrates.