Penial hard-on is caused by the engorgement of the phallus with stock. This engorgement occurs when the roue vessels delivering lineage to the member growth the obstetrical delivery of lineage and the line of descent vessels carrying profligate forth from the phallus step-down the removal of ancestry. Below formula conditions, sexual stimulus leads to the production and passing of chemical element oxide in the penis. Element oxide and then activates the enzyme, guanylate cyclase, which causes ...