Endocrine system is considered an important system of the body. This system governs different kinds of bodily activities by meeting with nervous system.
Endocrine system is made of the union of those tissues or organs which are called endocrine glands. These glands excrete a special chemicals into the extra cellular spaces and such chemical are called hormones from where these chemicals reach into blood system directly and reach in that special body organ by circulating with the blood of body where their function is required. Such kinds of glands have no vessels or ducts so they are called ductless glands.
Along with endocrine glands, there are exocrine glands too in the body as sweat gland, salvia glands, pancreas, liver, etc which have vessels and ducts. Their excretion reaches into a special organ by going through them and then does its work. Because it has vessels and ducts so they are called duct glands.