NO - nitric oxide - under construction

NO is a simple molecule, consisting of a single oxygen bonded to one nitrogen atom. 11 electrons in the outer shell of NO make the net spin of the molecule S = 1/2, which is responsible for NO high reactivity as a free radical, and its unique properties in terms of its action as a heme ligand.
Its very small molecular size and lipophilic nature allow the rapid diffusion of NO through plasma membranes and enable NO to communicate with neighboring cells, however, a short half-life in biological fluids (2 - 30 seconds) permits the molecule only for local action.

A vasculature is in constant state of active dilation mediated by NO. Endothelial cells, the most inner part of blood vessels, continuously release small amounts of NO which migrates to nearby muscle cells and binds to the heme group of guanylate cyclase (GC), the major target for NO. Activated GC produces cyclo-GMP, which, through a cascade of protein kinases, induces smooth muscle relaxation. This dilates the vessel and lowers blood pressure.
Endothelial generation of NO not only regulates blood pressure but also reduces blood clotting by acting directly on platelets. It reduces clotting by inhibiting platelet aggregation and adhesion.

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