What Is Blood Made Of?

Step 1 of 5

Over half of it is just liquid.

Plasma is water with salts, sugar and proteins dissolved in it. Every nutrient and every waste product travels dissolved in this river.

Step 2 of 5

Red cells are oxygen taxis.

Each one is packed with a molecule that grabs oxygen in the lungs and lets go of it in muscle. They are dented discs, which gives them more surface.

Step 3 of 5

White cells are the guards.

They are far rarer but far larger, and they patrol for bacteria and damaged cells. Pus is mostly white cells that have finished a fight.

Step 4 of 5

Platelets are the plug crew.

Tiny fragments that stick to a torn vessel wall and to each other, building a temporary dam while a proper scab forms over it.

Step 5 of 5

The whole volume goes round in about a minute.

Roughly five litres in an adult, pushed by the heart through a loop long enough to circle the planet twice if the vessels were laid end to end.

Blood looks blue through your skin only because skin scatters light oddly. Even the oxygen-poor blood in your veins is dark red.