cell or tissue that removes specific substances from the blood, alters or concentrates them, and then either releases them for further use or eliminates them. Typically, a gland consists of either cuboidal or columnar epithelium resting on a basement membrane and is surrounded by a plexus, or meshwork, of blood vessels. Endocrine (endocrine system), or ductless, glands (e.g., pituitary, thyroid, adrenal) secrete substances known as hormones directly into the bloodstream rather than through ducts. Exocrine glands (e.g., salivary, sweat, digestive) discharge their products through ducts.