A collection of CELLS or an ORGAN with a specialised ability to make and secrete chemical substances such as enzymes and hormones essential for the normal functioning of the body. Glands are classified into two groups: ENDOCRINE and EXOCRINE. The former secrete their products, hormones, straight into the bloodstream; the latter's secretions are discharged through ducts. (These functional differences are the reason why glands have been defined as ductless and ducted.) Examples of endocrine glands are the adrenals, PITUITARY GLAND and THYROID GLAND. Exocrine glands include SEBACEOUS glands (in the skin) and the SALIVARY glands in the mouth whose enzymes start the digestion of food. The BREASTS or mammary glands are exocrine glands that secrete milk. Though strictly speaking not a gland, LYMPH nodes (part of the lymphatic system) are sometimes called that. While they do not produce secretions, lymph glands do release white blood cells, an essential part of the body's defence system.