what is secretion in excretion
The synthesis and release of chemical substances by cells or glands. Substances secreted include enzymes, hormones, lubricants, surfactants and neurotransmitters. Internal secretion is secretion into the bloodstream. External secretion may be into the intestinal canal or other organs or on to the skin. Compare EXCRETION. 1  the process by which a useful substance produced in a cell is passed through the plasma membrane to the outside.  the substance itself.