exocrine refers to glands, or to secretions, where the discharge of the secretion is onto a body surface. This may be either onto the skin or onto one of the lining surfaces within the body: of the alimentary tract from the mouth to the anus; the respiratory tract from the nose down to the alveoli of the lungs; the urinary tract (urethra, bladder, ureters, and tubules of the kidneys); or the genital tract (vulva, vagina, uterus, and Fallopian tubes, or vasa deferentia and tubules of the testis). These tubes or cavities are all in continuity with the outside world, and exocrine secretions all deal in some way with the external environment, or with exchanges between it and the body. Thus secretions onto the skin (e.g. from sweat glands, sebaceous glands) deal with heat loss and surface protection; those into the gut (e.g. digestive enzymes, bile) deal with food; those into the respiratory passages (e.g. mucus, surfactant) with the filtering of inhaled air and facilitation of gas exchange in the lungs; those into the urogenital system with excretion and reproduction (e.g. substances in the urine, seminal fluid, cervical mucus). By contrast, endocrine refers to glands, or to secretions, where the discharge is internal, into the bloodstream.

Stuart Judge

ex·o·crine / ˈeksəˌkrin; ˈeksəˌkrēn/ • adj. Physiol. relating to or denoting glands that secrete their products through ducts opening onto an epithelium rather than directly into the bloodstream.Often contrasted with endocrine.

exocrine See ECTOCRINE.

exocrine See ECTOCRINE.