Secretion

in animal physiology, a substance separated usually from the blood by glandular activity. Secretions are of two kinds--helpful and detrimental. The urine is a detrimental secretion. Detrimental secretions are called excretions. The glands, which may be defined as groups of cells, occupied in extracting liquid or semi-liquid substance from the blood, have no power to manufacture. They simply collect material from the blood. The salivary glands collect saliva, the pancreas secretes pancreatic juice, the liver stores bile, and the mucous membrane supplies the alimentary canal with a moistening secretion known as mucous. The glands and secretions named, together with the gastric juice, may be grouped under the term digestive. Other secretions are the lymph, the synovial fluid, the oil of the hair, tears, perspiration, and ear wax.