Unlike most hormones, which are produced by glands and transported in the bloodstream to act on distant areas of the body, the prostaglandins are produced at the site where they are needed. Prostaglandins are produced in nearly all cells and are part of the body’s way of dealing with injury and illness. Prostaglandins act as signals to control several different processes depending on the part of the body in which they are made. Prostaglandins are made at sites of tissue damage or infection, where they cause inflammation, pain and fever as part of the healing process. When a blood vessel is injured, a prostaglandin called thromboxane stimulates the formation of a blood clot to try to heal the damage; it also causes the muscle in the blood vessel wall to contract (causing the blood vessel to narrow) to try to prevent blood loss. Another prostaglandin called prostacyclin has the opposite effect to thromboxane, reducing blood clotting and removing any clots that are no longer needed; it also causes the muscle in the blood vessel wall to relax, so that the vessel dilates