Prostaglandin. Computer graphic of a molecule of prostaglandin, a hormone-like chemical. It is an unsaturated fatty acid or lipid which has a broad range of physiological activity. The molecule's atoms are colour-coded: carbon is yellow, hydrogen is blue & oxygen is red. There are many types of prostaglandins, each with 20 carbon atoms, that are continually produced in mammal tissues. Their effects include lowering blood pressure, causing contractions of smooth muscle, regulating cell function & fertility, promoting inflammation, & affecting the platelet cells that form blood clots. They have localised effects because they are rapidly broken down once released by cells.