 Dear students, in this topic, we shall discuss in detail the prostaglandins. Prostaglandins are hormone-like local regulator substances. They are derived from cyclic, long chain, unsaturated hydroxy fatty acids. Up to now, 16 prostaglandins have been discovered. Prostaglandins are produced by all or nearly all tissues of the body. They are synthesized in the membranes from arachidonic acid which is produced by the cleavage of phospholipids by phospholipase enzymes. Dear students, Most prostaglandins play two or three roles. Some work as paracrine agents and keep a local effect. While some prostaglandins work as endocrine hormones and act on distant target tissues. On their target cells, they bind to cell surface receptors and are linked to cyclic AMP pathway. They produce a short-lived and rapid response just like the lipid insoluble hormones. Dear students, prostaglandins have diverse actions on various tissues. They have role in fertilization. They have role during labor. Their role is also present in blood clot formation. They are also involved in the maintenance of stomach lining and in the production of erythro-poietin hormone. They also regulate blood pressure. We shall discuss all these functions of prostaglandins in detail. First we shall discuss their role in fertilization. Semen produced by males has certain prostaglandins that aid our help in fertilization. These prostaglandins present in semen play two roles. One is to react with female cervical mucus and make it more receptive for the sperm movement. Second is to produce such contractions in the smooth muscles of the uterine wall that help the sperm to reach the egg. Now we shall discuss their role in labor i.e. childbirth. Placenta produced near the start of childbirth. These prostaglandins make the muscles of uterus more excitable by oxytocin. As a result the contractions of uterus wall are enhanced during labor. The role of prostaglandins in immune response is also very important. Damage tissues produce certain prostaglandins during immune response. These prostaglandins act as local regulators of inflammation. As a result they produce fever and inflammation. They also intensify the sensation of pain. Sensation of pain is also an important part of immune response which prevents the damage from other parts of the body. Prostaglandins enhance pain by increasing the sensitivity of nociceptors i.e. pain receptors. During immune response a substance called interleukin-1 is produced. This interleukin-1 produces a particular type of prostaglandin E2. E2 prostaglandin plays an important role in fever reactions because it acts on hypothalamus and produces fever reactions. Here is an important practical use of aspirin. In all these three symptoms, aspirin is used as an anti-piratic, anti-inflammatory and pain-relieving agent to block the synthesis of prostaglandins and as a result it gets relief from these three symptoms. Here students, now we shall discuss the role of prostaglandins in blood clot formation. Prostaglandins help in aggregating platelets and making blood clots and this is the reason why aspirin is also used as an anti-clot agent because it inhibits the formation of prostaglandins. Dear students, certain prostaglandins help to maintain the protective lining of stomach as aspirin interferes with the synthesis of prostaglandins so continuous use of this medicine causes damage of the stomach lining and as a result heart patients continue to use aspirin in stomach irritation or ulcer. Here students, prostaglandins also play an important role in the production of erythropoitin which is a hormone that stimulates the production of erythrocytes i.e. red blood cells. This hormone is produced by the kidneys and these prostaglandins affect the kidneys. Dear students, some prostaglandins act on smooth muscles of the blood vessels and cause them to their vasodilation or vasoconstriction. Both processes are regulated by blood pressure.