The glands of internal secretion, the glands of the endocrine system whose hormones are secreted directly into the vascular system.
Any one of certain glands in the body, the secretion of which goes directly into the bloodstream and so is carried to different parts of the body. These glands the pituitary, thyroid, parathyroid, adrenal and gonads are also known as the endocrine glands. Some glands may be both duct glands and ductless glands. For example, the pancreas manufactures a digestive juice which passes by a duct into the small intestine. It also manufactures, by means of special cells, a substance called insulin which passes straight into the blood.
A gland without ducts, secreting directly into capillaries one or more hormones that have specific effects on target organs or tissues.