Platelet Structure

Platelets are actually not true cells but merely circulating fragments of cells.  But even though platelets are merely cell fragments, they contain many structures that are critical to stop bleeding.  They contain proteins on their surface that allow them to stick to breaks in the blood vessel wall and also to stick to each other.  They contain granules that can secrete other proteins required for creating a firm plug to seal blood vessel breaks.  Also platelets contain proteins similar to muscle proteins that allow them to change shape when they become sticky. 

Platelet Function

In addition to being the smallest blood cell, platelets are also the lightest.  Therefore they are pushed out from the center of flowing blood to the wall of the blood vessel.  There they roll along the surface of the vessel wall, which is lined by cells called endothelium.  The endothelium is a very special surface, like Teflon, that prevents anything from sticking to it.  However when there is an injury or cut, and the endothelial layer is broken, the tough fibers that surround a blood vessel are exposed to the liquid flowing blood.  It is the platelets that react first to injury.  The tough fibers surrounding the vessel wall, like an envelop, attract platelets like a magnet, stimulate the shape change that is shown in the pictures above, and platelets then clump onto these fibers, providing the initial seal to prevent bleeding, the leak of red blood cells and plasma through the vessel injury. 

So the platelets are a very essential combat system.Thus we are definitely thankful to have those!😊