Blood, the heart and the vessels that carry blood around the body together make up the cardiovascular system. They are vital for carrying nutrients, oxygen and waste around the body.
Blood is made of cells and plasma. There are 3 main types of blood cells — red cells, white cells and platelets. All are made in the marrow found in many bones.
Red blood cells deliver oxygen from the lungs to the rest of the body and carry waste products to be released by the lungs or the kidneys. Red blood cells contain haemoglobin, which is the protein that binds and releases oxygen.
White blood cells are part of the immune system. They detect and fight infections or foreign molecules that enter the body.
Platelets are small cells that help the blood clot.
As well as carrying cells, nutrients, oxygen and waste, blood also helps to regulate body temperature.
What are blood vessels?
Blood leaves the heart in large arteries, then moves through progressively smaller ones to the capillaries in tissues. The blood then leaves the tissues in veins that get larger as they get closer to the heart.
The arteries can expand and contract to lower or increase blood pressure, according to your needs.