<prompt> NO is secreted byEndotheliumEndodermEctodermBones  <response>: Nitric oxide, known as an endothelium-derived relaxing factor EDRF, is biosynthesized endogenously from L-arginine, oxygen, and NADPH by various nitric oxide synthase NOS enzymes. Reduction of inorganic nitrate may also serve to make nitric oxide. The endothelium inner lining of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, thus resulting in vasodilation and increasing blood flow. Nitric oxide is highly reactive having a lifetime of a few seconds, yet diffuses freely across membranes. These attributes make nitric oxide ideal for a transient paracrine between adjacent cells and autocrine within a single cell signaling molecule.Ref: Ganong;s review of medical physiology 23rd edition Page no: 405 