False-colour scanning electron micrograph (SEM) of three types of cells found in human blood. At left is a red blood cell or erythrocyte,a biconcave disc that transports oxygen around the body. The white blood cell (centre) is spherical,with microvilli projecting from its surface. Different types of white cell are active in the body's immune response to infection. The wafer-like cell at right is a blood platelet,which functions to control clotting & thus prevents bleeding from damaged vessels. Each cubic millimetre of blood contains roughly 5,000,000 red cells,7000 white cells,& 250,000 platelets. Magnification: x575 at 6x6cm size,x385 at 35mm size. JBU full-colour version. The original BW is P242/103NIB |