The heart supplies blood to the body. Blood carries important materials which are required for the body to function and to keep healthy. These include nutrients and oxygen. Blood also helps to get rid of waste and carbon dioxide from the body, as well as fight infections. Blood is transported around the body via blood vessels. 

The blood vessels that carry blood around the body are arteries, capillaries, and veins.

Arteries carry blood away from the heart. This blood contains nutrients and water. Arteries supply this blood to the rest of the body. Arteries also transport blood from the heart to the lungs to be oxygenated.

The capillaries are essentially exchange center. They are tiny blood vessels that allow oxygen, carbon dioxide, nutrients, and water to move in and out of the bloodstream. Capillaries are located between the arteries and veins. They allow the exchange of materials between the blood and the surrounding cells.

Veins carry blood to the heart, so they transport deoxygenated blood, carbon dioxide, and other waste from the body back to the heart.

The components of blood are:

• Red blood cells
• White blood cells
• Platelets 
• Plasma 

Each component makes up a different proportion of the blood. Red blood cells make up around 45%, white blood cells and platelets make up around 1%, and plasma makes up around 55% of the blood. 

Red blood cells

Red blood cells are also known as erythrocytes. These are produced in the bone marrow. They carry oxygen and nutrients around the body. Red blood cells contain a protein called haemoglobin. Haemoglobin helps to carry oxygen from the lungs to the rest of the body. This is what makes blood the colour red. Carbon dioxide is then returned from the body to the lungs to be exhaled. 

White blood cells

White blood cells are known as leukocytes. These are nucleated cells that fight infections to keep us healthy, so when you get sick it is the production of white blood cells that helps you to fight the cause of your illness. 

Platelets

Platelets are also known as thrombocytes. These are fragments that help to stop bleeding and help to heal wounds by forming blood clots. So when you bleed from an injury or wound, it’s the platelets that work too quickly for blood clots to stop too much blood from bleeding out. 

Plasma 

Plasma is the yellow liquid in which red blood cells, white blood cells, and platelets are carried. Blood plasma contains mainly water and other useful waste products. It contains proteins and hormones which help with the body’s functions. Plasma also helps to regulate bleeding and clotting.