FACTS: Platelets, or thrombocytes, are the smallest cells (or cell fragments) in the blood. Under the microscope, they normally look like little disks, or plates!
The primary purpose of platelets is to prevent bleeding by creating blood clots. As platelets circulate through the bloodstream, they normally slide along the smooth surface of the blood vessels without sticking. However, if the smooth wall is ruptured, platelets are activated: they swell up, stick to the exposed rough patch, and extend filaments which can help seal the breach.