Our heart has 2 circulatary systems: one for the lungs, one for the rest of the body.
The path taken by the blood: Vena clava (vein) --> Left atrium --> Left ventricle (here you should talk about the valves' function: to prevent backflow of blood) --> Pulmonary artery --> Lungs --> Pulmonary vein --> Right atrium --> Right ventricle (valves) --> Aorta --> Rest of the body
Parts of blood: Red Blood Cells - carry oxygen around body, large surface area due to their biconcave shape and no nucleus. Platelets - Clotting of the blood. Plasma - for transportation of carbon dioxide, urea, hormones and distribution of blood. White blood cells - (phagocytes)
Vena clava - the biggest vein Aorta - the biggest artery in the body