Blood is a vital fluid tissue, and it's made up of four main components. These are red blood cells, white blood cells, platelets, and the liquid they are all transported in, which is called plasma.

Plasma is the straw-coloured liquid part of the blood. Its main job is transport. It carries the blood cells around the body, but it also transports many other dissolved substances like ions, nutrients, urea, and hormones. It also transports carbon dioxide.

Red blood cells are the most numerous cells in the blood. Their single, crucial function is to transport oxygen from the lungs to the body's tissues. To do this, they contain a special red protein called haemoglobin.