Picture of blood

We probably don’t think about blood much, unless we cut ourselves or have to go for a blood test.

Most adults have around five litres of blood. That's more than a gallon. Blood does vital tasks around the clock, circulating around the body delivering oxygen and nutrition where it is needed and removing waste.

Blood flows through blood vessels, the arteries and veins, in the body.

Blood carries important cells and proteins as well as plasma. Plasma makes up about half of the volume of blood and carries proteins to help the blood clot, glucose and other nutrients.

About half of blood volume is composed of blood cells:

• Red blood cells, which carry oxygen to the tissues
• White blood cells, which fight infections
• Platelets, smaller cells that help blood to clot